c/EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
Commercial
Feasibility of
Recovering Tomato
Processing Residuals for
Food Use
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are
1 Environmental Health Effects Research
2 Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9 Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en
vironmental degradation from point and non-point sources of pollution This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through (he National Technical informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-202
September 1978
COMMERCIAL FEASIBILITY OF RECOVERING TOMATO PROCESSING
RESIDUALS FOR FOOD USE
by
W. G. Schultz, H. J. Neumann , J. E. Schade
J. P. Morgan, P. F. Hanni
Western Regional Research Center, Science and Education Administration
U.S. Department of Agriculture, Albany, California 94710
and
A. M. Katsuyama, H. J. Maagdenberg
National Food Processors Association, Western Research Laboratory
Berkeley, California 94710
Interagency Agreement EPA-IAG-D5-0795
Project Officer
H. W. Thompson
Food and Wood Products Branch
Industrial Environmental Research Laboratory
Corvallis Field Station
Corvallis, Oregon 97330
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on
our health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory-
Cincinnati (lERL-Ci) assists in developing and demonstrating new and im-
proved methodologies that will meet these needs both efficiently and econo-
mically.
This report presents the results of a 2 year study on the techno-
economic feasibility of recovering a food grade material from the peel
residue associated with the "dry" caustic peeling of tomatoes. The overall
purpose of the project was to develop a beneficial use of a food processing
residual which is currently considered a waste material. The results of
this study should be of interest to tomato processors, regulatory agencies,
manufacturers of specialty food chemicals and food researchers. For further
information on this study, contact the Food and Wood Products Branch,
Industrial Pollution Control Division, lERL-Ci.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
ill
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ABSTRACT
In the United States tomatoes are typically peeled for commercial
canning by first immersing them in a caustic bath to loosen the skin; then,
the peel is removed either mechanically with rubber discs or with water
sprays. When the peel is removed mechanically, the peel solids are not
diluted and therefore, are similar to the pulp of whole tomatoes. Since
this removed peel is at least 12% of the unpeeled weight and the peel is
about 96% pulp, this peel pulp is a good source of potential food material.
There are about 1.3 million tons of tomatoes peeled each year in the United
States, resulting in at least 150,000 t/yr of recoverable pulp. Currently
that pulp is discarded as peel at an expense of at least $2.50/t or $12.00/hr.
Pulp recovery is attractive economically because it has a projected net
worth of $187/hr for a typical 40 t/hr peeling operation. The estimated
overall net return per cannery is $199/hr, including processing expenses.
This is a $7,500,000/yr potential gross return 'to the United States tomato
processing industry and provides a corresponding ability to maintain lower
product prices to the consumer.
A 2-year project was undertaken to determine the commercial feasibility
of recovering pulp from the peelings of caustic peeled tomatoes. In 1975,
peel from regular cannery operations was processed through a 20-gpm (5 t/hr)
continuous-flow line. This processing consisted of acidifying the peel to
pH 4.2 with food-grade hydrochloric acid, then separating the pulp from
the skin with a paddle finisher (screen). Recovered peel pulp was found
to be of food quality but contained high peeling-aid residues (150-450 ppm).
Practically all tomato peeling operations use a peeling aid in the caustic
bath to facilitate uniform peeling. Peeling aids in current use are approved
for peeling but not as additives to the final product. In 1976, a 1-t/hr
pilot peeling line was set up at a cannery to study modifications in the
peeling process for the purpose of reducing peeling-aid residue in the
recovered pulp. The principal modification was to pretreat the tomatoes
by immersion in a 150°F aqueous bath (approximately pH 3.6) containing about
0.15% food-grade octanoic (caprylic) acid; subsequently, the tomatoes were
immersed in caustic. The peel was removed with rubber-disc peelers.
Recovered pulp met USDA Quality Grade A, and the octanoic acid levels were
low (0 to 30 ppm). The proposed use of this recovered peel pulp is in com-
bination with tomato pulp from regular sources for canned products such
*This report follows the prevailing canning industry practice of using the
International System of Units (SI) in the laboratory and U.S. units in the
manufacturing operations. See TABLE OF CONVERSION FACTORS for U.S. to SI
units.
iv
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as tomato sauce, catsup, paste, and fill juice for peeled tomatoes. Compo-
sitions of these products are governed by the FDA Standards of Identity,
currently being revised; the current regulations allow the use of liquid
from peels and cores but do not address the use of pulp from caustic peels.
This project was funded jointly by United States Department of
Agriculture-Western Regional Research Center, National Food Processors
Association-Western Laboratory, Environmental Protection Agency, and the
California tomato processors. This report was submitted in fulfillment of
Interagency Agreement EPA-1AG-D5-0795 under the partial sponsorship of the
U.S. Environmental Protection Agency, and covers a period from May 1, 1975
to August 31, 1977. The experimental and analytical work was completed
as of July 15, 1977.
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CONTENTS
Foreword
Abstract ............................. iv
Figures ........................... .' .' '
Tables ..............................
Abbreviations and Symbols ..................... ix
Conversion Factors for Units .................... x
Acknowledgments ..........................
1. Introduction ....................... 1
2. Conclusions ........................ 4
3. Recommendations ...................... 5
4. Materials and Control Instruments ............. 6
5. Experimental Procedures .................. 9
6. Results and Discussion, General .............. 26
Washing and Sorting ................. 28
Peeling Aids ..................... 28
Carboxylic Acid Peeling ............... 30
Peeling-Aid Pretreatment ............... 30
Modified-Caustic Peeling ............... 31
Peel Removal ..................... 31
Peel Flow ...................... 32
Peel Alkalinity ................... 32
Acidification .................... 34
Salt (Sodium Chloride) ................ 34
Pulp Extraction ................... 35
Vacuum Evaporation .................. 38
Unit Operation Times ................. 39
Product Color, Flavor, and Vitamins ......... 40
Consistency, Viscosity, and Pectin .......... 41
Amino Acids ..................... 45
Product Mold, Insect Fragments, and Bacterial Counts . 45
Pesticides ...................... 46
U.S. Standards of Identity .............. 47
Effluents and Wastes . ................ 49
Economics ...................... 51
References ............................. 52
Bibliography . ........................... 55
Appendices
A. Vitamin A Activity Method ................. 56
B. Photometric Determination of Anionic Peeling Aids ..... 59
C. Determination of Fatty Acids in Processed Tomato Products . 62
vii
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FIGURES
Number Page
1 Tomato peel component diagram 2
2 1975 process flow diagram 10
3 1975 equipment profile n
4 Peel tank, 1975 12
5 Hot break vessel, 1975 13
6 Tramp metal trap, 1975 14
7 Modified caustic peeling, 1976 17
8 Acid required to reduce pH of caustic peel and pulp 33
TABLES
Number
Page
1 Summary of Typical 1975-1976 Recovered Peel Pulps 27
2 Acidification Data, 1975 35
3 Summary of 1975 Processing Conditions and Solids Recovery ... 37
4 Unit Operations Times, 1975 40
5 Storage Stability of Recovered Pulp, 1976 42
6 1976 Canned Samples of Recovered Pulps, 1976 43
7 Pesticide Residues in Recovered Peel Pulp 48
8 Projected Economics of a Commercial Installation 51
viii
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ABBREVIATIONS AND SYMBOLS*
ACS — American Chemical Society
C — degrees Celsius (also, carbon in chemical formulas)
ca — about
COD — chemical oxygen demand
F — degrees Fahrenheit
ft — foot
g — gram
gal/t — gallons per ton
GLC — gas-liquid chromatography
gpm — gallons per minute
HC1 — hydrochloric acid
hp — horsepower
in. — inch
IU — International Units
Ib/gal — pounds per gallon
1/min — liters per minute
mg — milligram
ml — milliliter
mM — millimoles
mp — millimicrons
N — solution normality
NaCl — sodium chloride
NF — National Formulary
NTSS — natural tomato soluble solids
NTTS — natural tomato total solids
pH — hydrogen ion concentration, log 1/(H )
ppm — parts per million
psig — pounds per square inch, gauge pressure
QC — quality control
rpm — revolutions per minute
t/hr — tons per hour
t/yr — tons per year
TS — total solids
w/v — weight per volume
w/w — weight per weight
*This report follows the prevailing canning industry practice of using U.S.
(English) units in the manufacturing operations and Metric (SI) units in
the laboratories. See CONVERSION FACTORS FOR UNITS on page ix.
ix
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CONVERSION FACTORS FOR UNITS
U.S. Units
F
ft
gal
gpm
gal/t
(F-32) 0.5556
(ft) 0.3048
(gal) 3.785
(gpm) 3.785
(gal/t) 4.172 x 10~J
hp (electric) (hp) 746.0
in. (in.) 0.02540
Ib/gal (Ib/gal) 0.1198
psig (psig + 14.7) x 6894
t (short) (t) 907.2
Metric (SI) Units
C, degrees Celsius
m, meter
1, liters
1/m, liters per rain
I/kg, liters per kilogram
W, watts
m, meter
8/cC» gram per cubic centimeter
N/m , newton per sq. meter
(absolute)
kg, kilogram
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ACKNOWLEDGMENTS
The authors appreciate the support given to this project by the tomato
processing industry; not only did it ease the burden, but tasks and judgments
were often shortened and made possible in a few months which otherwise might
have required several years. In particular, we wish to thank Tillie Lewis
Foods and Hunt-Wesson Foods at whose canneries the field work was performed.
Their participation allowed a practical approach that could not be duplicated
in a laboratory or pilot plant. The U.S. Environmental Protection Agency
supported this experimentation in part, thus enabling the work and develop-
ment to be carried out in the short period of 2 years.
xi
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SECTION 1
INTRODUCTION
In the United States tomatoes are normally peeled by loosening the skin
with a hot-caustic bath and removing the peel (skin with adhering pulp, see
Figure 1) either mechanically, such as with rubber discs, or with water
sprays. The use of water sprays has declined because of the large amount of
water needed (500-1,500 gal/t*) and the subsequent problem of waste disposal
of the dilute solution. Removal of the peel mechanically with rubber discs
reduces the water consumption to a neglible amount so that the peel has about
the same solids content as fresh tomatoes. This material is currently dis-
carded as solid waste and constitutes at least 12% of the original tomato
weight. Since this peel is about 96% pulp, it is a potential source of food
material. This pulp has a value of up to $50/t as recovered pulp, and from
a typical 40 t/hr peeling operation, at least 5 t/hr of peel is available
with a gross value of $250/hr of operation. Currently that pulp is discarded
as peel at an expense of at least $2.50/t. Since there are about 1.3 million
tons of tomatoes peeled each year in the United States resulting in at
least 150,000 t/yr of recoverable pulp, there is a potential gross value
of $7,500,000/yr, and a corresponding opportunity to hold down the product
price to consumers.
Despite the economic incentive, there were several technical obstacles
such as insecticide residues, residuals of the caustic and surfactants from
the caustic-peeling applicator, acidification of the alkaline peel, recovered-
pulp quality, product labeling, etc. With these potentials and obstacles in
mind, a two-year project, beginning in 1975, was undertaken jointly by the
U.S. Department of Agriculture (USDA)-Western Regional Research Center,
National Food Processors Association (NFPA)-Western Research Laboratory,
and the tomato processing industry. The initial plans were described in
April 1975 (1) and were based on trends in commercial practice and prior
information on pulp recovery potential (2) (3) (4) (5).
Utilization of tomato peel was considered during pilot tests on the
mechanical, rubber-disc peel removal system in 1973 (2). In a single,
large-scale test conducted in 1974, pulp was prepared from tomato peel (3).
Until recently tomato peel was removed with water sprays after caustic
immersion, resulting in too dilute a peel for practical pulp recovery.
As more of the rubber disc, mechanical peel removal units have been
installed, more peel is available that retains the solids concentration
of a fresh tomato; thus pulp recovery from the peel is now practical.
*This report follows the prevailing canning industry practice of using U.S.
(English) units in the manufacturing operations and Metric (SI) units in
the laboratories. See CONVERSION FACTORS FOR UNITS on page ix.
1
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PEEL
PEELED
TOMATO
PULP
Figure 1. Tomato peel component diagram.
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Consideration was also given to utilization of additional tomato solids
derived from tomato pomace through an acid treatment similar to that
demonstrated with macerate (A) (5).
The recovery is accomplished by acidifying the peel, then separating
the peel into pulp (96%) and skin (4%) fractions. Skin is discarded. The
recovered peel pulp contains salt and could be used in formulating tomato
sauce or similar salted products. The experimentation, developments, and
analyses spanned two processing seasons from June 1975 through December 1976.
The 1975 experimentation centered on a continuous processing of peel from
a regular cannery peeling operation, taking the peel as discharged from nor-
mal operations. The primary goal was to evaluate the commercial feasibility
of recovering tomato peel pulp as food-grade material from tomato peelings
and pomace. The material evaluated was 100% pulp (from peel) without combi-
nation with other tomato material as would be expected in normal cannery
operation. This permitted the true identity and character of the recovered
pulp to be evaluated in terms of the USDA Standards for Grade and FDA Stand-
ards of Identity.
During the first year of experimentation, the peelers were operated by
the cannery personnel to conform to production needs, and experimentation
involved only the pulp recovery which had to adapt to the cannery operation
without any influence by the experimenters. Originally, 1976 was projected
to emphasize process optimization with the caustic peel residual. However,
as a result of the high peeling-aid residues found in 1975, work in 1976 was
primarily developmental and emphasized the reduction of this peeling-aid
residue in the recovered pulp.
The present FDA Standards of Identity for tomato pulp allow material
from several sources. One source is the liquid obtained from peel residuals
resulting from tomato peeling operations. The present (1976) Standards were
written when steam and water peeling were prevalent. Those Standards are
being revised, and it is expected that the revised Standards will be avail-
able in 1978.
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SECTION 2
CONCLUSIONS
1. Tomato pulp can be recovered from caustic peel which amounts to 15%
or more of the fresh tomato weight. Current practice is to discard
the caustic peel. When acidified and screened, about 96% of the peel
is recoverable pulp, and 4% is waste skin. Therefore, waste disposal
volume is reduced by 96%.
2. Recovered pulp can meet USDA Grade A Standards for color, flavor, and
absence of defects.
3. The recovered pulp contains salt, has an intense red color (maximum
Grade A score), has a thick consistency that is due to insoluble mate-
rials, and is suitable for use in sauces, etc.
4. The preferred method of controlling the peeling aid level in the
recovered pulp is an octanoic (caprylic) acid pretreatment of the
tomatoes, instead of using peeling aid directly in the caustic applica-
tor. Although steam-peelable tomatoes can be peeled by octanoic acid
alone (without caustic), caustic is generally needed for current
California varieties such as VF-145B-7879.
5. Pulp recovery is an economically feasible process in which the capital
investment can be recovered in 1-year; thereafter, the net return is
about $200/operating hour for a 40 t/hr caustic peeling operation.
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SECTION 3
RECOMMENDATIONS
1. Industry should seek regulatory clarification and acceptance of the
process and products associated with the recovery of pulp from caustic
peel, particularly on the: (a) pulp, (b) acidification, and (c) use
of octanoic (caprylic) acid.
2. Industrial (long-term) demonstrations on a full-scale processing basis
are needed to determine: (a) the pretreatment bath stability and
replenishment frequency, (b) the extent of peeling-aid carryover to the
caustic bath and into the product, and (c) the safety requirements such
as the need for flow-diversion of off-control material.
3. Each cannery needs to determine the optimum process flow, equipment,
and pulp use for its local situation.
4. A rapid, fatty-acid analysis should be developed to facilitate control
of the octanoic acid (caprylic acid) peeling-aid concentration in the
pretreatment bath to aid process control by cannery production personnel.
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SECTION 4
MATERIALS AND CONTROL INSTRUMENTS
Tomatoes—In both years the tomatoes were field run as used by the
canneries. There was no selection for experimental use; it was felt that
any selecting would build in bias, and such selection would not be readily
identifiable. In a peeling operation it is the extremes of tomato peela-
bility that sets the conditions rather than the average tomato. Tomato
peelability was judged using 10-lb samples taken from each run of 2,000
Ibs. In 1975, the cannery processed the variety VF-145 almost solely. In
1976, the variety was usually the UC-134, with occasional varieties 198
and VF-145. Since a control run was made each day, the comparisons in
peeling were based on peeling variables, eliminating the need to consider
the tomato variety, harvest period, or growing location.
Sodium Hydroxide—The "caustic" (50% w/w sodium hydroxide aqueous solu-
tion; also called caustic soda or lye) used by canneries and in the pilot
peeling studies was a standard food grade manufactured by the electrolytic
diaphragm process. Currently, the chlor-alkali industry generally uses
an asbestos diaphragm to produce the sodium hydroxide. A discussion on
asbestos with respect to the chlor-alkali industry and its products was
presented in 1975 (35).
Proposed rules have been published by the Food and Drug Administration
regarding asbestos fibers in foods (6,7). However, as yet there have been
neither conclusions about the medical significance of ingested asbestos
fibers nor regulations promulgated on this subject.
Limited analyses were made in both years to determine the asbestos
content in the recovered pulp, in the caustic bath, and on field-run
tomatoes before and after washing. Although washing reduced the quantity
of soil-borne asbestos on the whole tomatoes, asbestos fibers were found
in the recovered pulp. The levels were about the same as have been repor-
ted as background in California drinking waters. Results from the limited
number of analyses indicate that the major contributing source of asbestos
is field soil, not the caustic bath.
The electrolytic mercury cell was formerly used by the chlor-alkali
industry, but caustic soda from this process is no longer generally available,
There is a newer caustic production process which utilizes an ion-exchange
membrane, hence avoiding the use of either mercury or asbestos, but material
so produced is also not generally available (8).
Hydrochloric Acid—In both years, the hydrochloric acid was a standard
commercially available food grade 22° Baume (35.21% w/w HC1, 9.84 Ib/gal).
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In 1975 it was received from a bulk truck and stored in a 500 gal plastic
tank provided with a calcium carbonate scrubber to control acid fumes.
Peeling Aids—These were commercially available sodium 2-ethylhexyl
sulfate (40% aqueous solution), sodium mono- and di-methyl naphthalene sulfo-
nates (40% aqueous solution), a proprietary mixture of C5 to Cg saturated
fatty acids with an odd number of carbons (Faspeel, BASF Wyandotte Corp.,
Wyandotte, Michigan), hexanoic acid (caproic acid, 99%), and octanoic acid
(caprylic acid, 92%). Faspeel is available only from the one source; all
the others have multiple sources and are sold under a variety of trade names.
Peel pH Recording Controller—This Leeds and Northrup (North Wales,
PA) pH equipment was a standard commercially available instrument, origin-
ally purchased in 1969, and used without modification other than to replace
electrodes. It consisted of Leeds and Northrup Type No. 992-820-0925-6-
008-485 having a Model R recorder, Series 80 electro-pneumatic controller
with a pH 0 to 10 range and 3 to 15 psig output, and used an Electrode
Assembly No. 7782 containing Measuring Electrode No. 117089, Reference
Electrode No. 117106, and Temperature Compensator No. 352145. These units
were suitable for tomato pulp at temperatures ranging from 80 to 212°F.
Final Pulp pH Recorder—Same type of unit as that used for Peel pH
Recording Controller.
Incoming Peel pH Recorder—Prior to acidification and irrespective of
the place of acidification, the incoming caustic peel was monitored by a
Beckman (Fullerton, CA) Type No. 8710-2-04-4-1-0-0-1 Recorder with a pH
4 to 14 range and using a pH Electrode Station Model No. 300-0-1-03-1-2-1-0,
containing a No. 636460 Remote Amplifier-Transmitter, No. 19033 Reference
Electrode, No. 19505 Measuring Electrode, and a No. 19586 Temperature Com-
pensator.
Laboratory pH Meter—Corning (Corning Scientific Instruments Co.,
Medford, MA) Model 475010 bench-type indicating meter with a pH 0 to 14
range and having a Beckman Combination Electrode No. 476051 and Corning
Automatic Temperature Compensator No. 476097.
Acid Control Valve—Acid addition was modulated by a Research Control
Valve (Research Control Co., Tulsa, OK) Type 75HB (Hastalloy B) with a 1/4-
in. body, an orifice of Cy - 0.30 equal percentage, and with a pneumatic
actuator for 3 to 15 psig signal from the pH Recording Controller, air-to-
open.
Hot-Break Temperature Controller—A standard thermocouple type instru-
ment and pneumatic actuated steam modulating valve were used. The recording
controller was a Honeywell (Philadelphia, PA) No. Y152P(13)-PH-96-Kl-(13)
with a 0 to 300°F range, 3 to 15 psig pneumatic output, and temperature
sensing with a Honeywell No. 2T1M13G6-5 Type T copper constantan sheathed
thermocouple. The controller was equipped with both proportional band and
reset, but with the relatively large volume of liquid to be heated, the
proportional band was quite adequate without reset.
-------
Pretreatment Temperature Controller—Same as the Hot Break Temperature
Controller.
Lye Applicator Temperature Controller—Same as the Hot Break Temperature
Controller.
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SECTION 5
EXPERIMENTAL PROCEDURES
1975 EXPERIMENTATION—PEEL PROCESSING AND PULP CHARACTERIZATION
A flow diagram of the 1975 cannery peel-pulp recovery system is shown
in Figure 2. Peel was experimentally processed on a daily basis during 1975
using peel as received from conventional caustic peeling at the Tillie Lewis
Foods, Plant W, Antioch, California. This cannery processed VF-145 tomatoes
through washing and sorting, then about 40 t/hr were diverted to their peeling
operation. The diverted tomatoes were next immersed in a caustic bath; this
was a typical industrial situation using 10-12% w/w sodium hydroxide with up
to, but not exceeding, 0.2% w/w sodium 2-ethylhexyl sulfate at 200-210°F and
with a nominal half-minute immersion. From this bath the tomatoes went into
two types of mechanical peel removers, a flat-bed disc type followed by peel-
tag removal rolls (FMC PR-20 Tomato Peel Remover, 1 machine; FMC Corporation,
San Jose, California) or rotary-cylinder, rubber disc types (Magnuson
Model C Peel Scrubbers, 4 machines; Magnuson Engineers, Inc., San Jose, Cali-
fornia). All of these peel removers discharged the tomato peelings into a
central screw conveyor which in turn emptied into a receiving tank. At this
tank the peelings were picked up by a centrifugal pump and sent through a
3-in. stainless tube a distance of 200 ft to an outside yard where the
experimental process equipment was located. At this yard the peelings passed
into the experimental process system (Figure 3) or into the cannery waste-
peel tank. In general, the experimental system utilized peel pumped directly
from normal cannery peeling operations, and received this about 5.4 minutes
after the clean tomatoes first entered the caustic applicator. This peel was
"normal" material rather than closely controlled laboratory samples.
The primary experimental variables in the pulp recovery system were:
(1) the extractor screen size and paddle clearance, (2) place of acidifi-
cation, either before or after fractionation of pulp from the skin and
miscellaneous seeds and fibers, (3) hot-break temperature, (4) lag time
between the hot break and canning, (5) evaporator temperature and degree
of pulp-solids concentration, and (6) the heat-processing time of cans.
These variables were evaluated in terms of: (1) pulp yield, (2) product
quality, and (3) tomato Standards of Identity.
Peel was received continuously at 10-30 gpm, and acidified with food-
grade hydrochloric acid either immediately in the Peel Tank (48 gal pulp
volume, Figure 4) or later in the Hot-Break Vessel (250 gal pulp volume,
Figure 5); this acidification was continuously controlled by an automatic
pH recording controller. Peel flowed continuously into each of these
vessels and constant volumes were maintained by overflow weirs. A tramp-
metal trap (Figure 6) was used to protect the pumps and other equipment.
-------
CONVENTIONAL PROCESSES
EXPERIMENTAL PROCESS
1
FIELD
PUREE
f
WASH
t
SORT
t
CRUSH
t
HOT BREAK
t
PULP
•- •—
t
FINISH
t
i
CONCENTRATE
t
1
CANNING
(S)=SAMPLE POINT
1 1
RUN TOMATOES
| PEELING
1
WASH
t
SORT
f®
CAUSTIC DIP©
t
PFFI DFMfWAI
fc\
INSPECT
"OMACE f PULP0
CANNING ®
t
CONCENTRATED
(S
\i
ACID
t
^ rbbLINvjb
1
EXTRACTOR
, t
1
(ACIDIFICATION)
HOT BREAK (HEATING)
1
®
D
s
t
* CAN
i
t
HEAT
PROCESS
t
COOL^
Figure 2. 1975 process flow diagram.
-------
PEEL FROM
CANNERY
OPERATION
DISCARD
-
-------
PEEL RECEIVED 19* HT
(SUBMERGED INLET)
PEEL pH RECORD
ELECTRODE ASSY.
10
ACID DIFFUSER
(1" ABOVE AGITATOR
LEVEL)
PEEL
OUTLET
WEIR
BAFFLE EXTENDS
TO TANK BOTTOM
AGITATOR,
10" O.D.
0" OFF BOTTOM)
350 rpm
°0°
f
t-PEEL pH CONTROLLER
ELECTRODE ASSY.
PEEL TANK
33%" I.D. x 36'/2" HT.
141 GAL. GROSS VOL.
48 GAL. OPERATING VOL.
Figure 4. Peel tank, 1975.
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STEAM COIL, 69 rpm
24" COIL OD, 1.5" OD TUBE,
23 TUBE TURNS, TWO 4n x
84" PADDLES ON COIL OD,
55 tq ft HEATING SURFACE
COIL DRIVE, 3 hp
STEAM FLOW CONTROLLED
AUTOMATICALLY BY
PULP TEMPERATURE
30"
• ---- 1
CONDENSATE OUT
STEAM
IN
Figure 5. Hot-break vessel, 1975.
13
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2" ACME SANITARY |
FERRULE
IN
SHELL 611 DIA. x
0.062" WALL, x 24" LEN.
TYPE 304 S.S.
U
3" CLEANOUT^ fe
J OUT
Figure 6. Tramp metal trap, 1975.
-------
A Hot-Break Vessel (Figure 5) was provided to inactivate enzymes that
might be present and to reduce subsequent microbiological growth by avoiding
holding at the incoming 120°F pulp temperature for an extended period.
This heating also provided thermal-exposure testing since caustic exposed
tomato pulp is more susceptible to color and flavor changes than material
which has only been processed at the normal tomato pH of 4.2-4.5.
Next the pulp flowed into the Pulp Tank for a final check and record-
ing of pH. A material (mass) balance was made for each trial by weighing
the Extractor waste (primarily skin and seeds) and measuring the volume of
the recovered pulp. Recovery was determined with 400-1,000 gal. batches;
the weight of the recovered pulp and Extractor waste was equal to that of the
incoming peel. Recovered peel pulp was concentrated in 1,000 gal. batches
at 160-200°F to concentrations of 10-20% TS (total solids) in the cannery
single-stage vacuum evaporator.
The pH was measured and recorded at three positions in the process:
(1) the incoming peel pH was continuously recorded, (2) the acidification
was controlled and recorded at the peel tank or optionally at the hot break,
and (3) the final pulp was continuously recorded. The acid diffuser in the
peel tank was a 1/2-in. Schedule 80 plastic (Kynar) pipe drilled with 14
holes, 0.062-in. diameter on 1/2-in. centers. This acid diffuser was posi-
tioned as shown in Figure 4. Mixing was quite violent at the 350 rpm agitator
speed, and the alkaline peel reached pH 4.2 within an estimated five seconds
of entering the mixing portion of the tank. The diffuser for the Hot Break
Tank had 16 holes, 0.062-in. diameter on 2.75-in. centers, and was positioned
at the inlet end of the tank, parallel to the coil axis; the pH electrode
assembly was on the outlet end.
Both fresh and canned samples were made up for subsequent analyses. All
canned samples were hand filled into size 211 x 400 unenameled cans, sealed
with a double seamer, heat processed in boiling water for 40 minutes, and
cooled to 100°F in 75°F water. These canned samples were analyzed and judged
on a 100% recovered-pulp basis without blending into other tomato materials.
1976 LABORATORY STUDY ON PEELING AIDS
The 1976 laboratory experimentation was primarily directed towards sol-
ving the peeling-aid residue problem which was identified during the 1975
pulp-recovery experimentation. In the spring, laboratory peeling tests were
conducted on tomatoes using about 70 compounds, including many surfactants
(surface-active agents), to determine the chemical structure that best aided
peeling. The wetting action (interfacial tension) of the potential peeling
aids was checked, but surface-wetting action alone was found to provide
little assistance in selecting peeling aids because enhancement of peeling
seemed to be primarily due to chemical activity. Potential peeling aids
were applied in two ways: (1) directly in the caustic bath in the tradi-
tional manner, and (2) as a pretreatment prior to immersing the tomatoes
in the caustic bath. The purpose of the pretreatment was to apply only
enough peeling aid to permeate the skin and assist the caustic to act more
effectively in the caustic applicator. It was also assumed that the
15
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optimum temperature and immersion time for applying the peeling aid might
differ from those used for the caustic application.
1976 PILOT SCALE MODIFIED CAUSTIC PEELING
Modified caustic peeling is the term used to indicate the application
of the peeling aid as a pretreatment prior to immersion of the tomatoes into
caustic (Figure 7). The best peeling conditions found in the laboratory
tests were incorporated in a 1-t/hr pilot line at Hunt-Wesson Foods, Plant A,
Hayward, California during the 1976 tomato processing season. This line
operated on the regular cannery tomatoes, usually Variety UC-134. Final
washing, sorting, and peeling were carried out solely on the pilot equipment.
Peeling was performed continuously, typically in 45 minute runs, with samples
taken during steady-state conditions.
This Hayward cannery received tomatoes usually in bulk 20-t loads (trac-
tor with two trailers) as is typical for California canners. The tomatoes
were removed from the trucks by the cannery personnel through a water wash-
out and carried by a flume into a sump; from the sump, they were elevated
out and spray washed, passed over a screen to remove gross trash and toma-
toes less than 1.2-in. in diameter and then flumed. Prior to further cannery
washing and sorting, part of the tomatoes were diverted from this flume to
the pilot-peeling line.
In the experimental system these tomatoes were immersed in water, eleva-
ted out, and passed over a 1-ft x 10-ft rubber disc flat-bed scrubber having
water sprays (10 gpm total); this was the final washing. The tomatoes were
then passed over a sorting belt for hand sorting; the degree of hand sorting
was varied to compare mold counts in the recovered pulp. The pretreatment
immersion was in a 17-in. x 10-ft trough having a paddle type, positive dis-
placement conveyor which controlled the immersion time. Immersion time could
be varied from 15 seconds to three minutes. The heated solution was recircu-
lated from entry to exit at about 20-gpm, and was controlled and varied from
75°F to 200°F, depending on the experiment. From this pretreatment, the
tomatoes were removed on an open-mesh elevator for a variable draining time
of 10-seconds to 2 minutes. After draining, the tomatoes dropped into the
Caustic Applicator for a 10-sec to 2-min immersion time in 11% (w/w) sodium
hydroxide at 210°F. A commercial applicator, such as the FMC Hi-Ton Tomato
Peeler, has a drain period of about 50% of the immersion time, which not only
removes excess caustic solution but provides a further period for the caustic
to act on the tomato. The pilot caustic applicator did not have a similar
drain period so this was simulated by a variable-speed, open-mesh belt nor-
mally held to 11 seconds residence time. Tomatoes then passed over rotating
slitting blades and onto a 12-in. x 10-ft set of flat-bed rubber-disc peel
removers which were operated without water sprays to provide undiluted peel.
This unit was the same as that used for washing and had discs of 4.25-in.
diameter, spaced 0.9-in. apart, on 3-in. centers, and turning at 425 RPM in
the direction of the tomato travel; the bed was pitched upward 10-in./10-ft
in the direction of the tomato travel which gave a nominal tomato residence
time of 30 seconds. This dry removal of peel is increasingly being practiced
commercially.
16
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WASH [-*-j SORT
PRETREATMENT
MATERIAL
BALANCE
[HOLD [—>-| SLIT | >-| PEEL REMOVAL | *»- PEELED TOMATOES (Pdt) 85.o%
, , 7 ,—z;
I ACID I »- PEELINGS >»] FINISHER | »- SKIN (waste) 0.6%
v PEEL PULP (product) 14.4%
100.0%
Figure 7. Modified-caustic peeling, 1976.
-------
Peel dropped onto a full-length pan and flowed down to a 10-gal. pot
where the peel was acidified, then separated into skin and pulp fractions
with a Langsenkamp Indiana Laboratory Pulper (Langsenkamp Inc., Indianapolis,
Indiana) equipped with a 0.033-in. screen. This recovered pulp was hot
filled at 115-190°F into 211 x 400 enameled cans, processed for 45 minutes
in boiling water, and cooled to about 100°F in 75°F water. For a material
balance on each trial, both the recovered pulp and peeled tomatoes were
weighed, typically 1,000 to 2,000 Ib/trial.
A typical set of experiments would involve altering one variable, such
as pretreatment temperature, residence time, peeling-aid concentration, or
the type of peeling aid. The first run would be with plain caustic preceded
by a pretreatment, for example, at 150°F, 0.5 minute immersion in the pre-
treatment bath, without peeling aid. The weight percent of peeled tomatoes
was calculated from the tomatoes in a 10-lb sample which had at least 99%
of the peel removed. The pan under the rubber discs would catch the peel
which would be swept into a pot and acidified every 4 to 8 minutes with
hydrochloric acid. This acidification time corresponded to the delay between
peel removal and acidification experienced in 1975. When peeling at 2,000
Ib/hr, there was insufficient peel to screen continuously; therefore, the
acidified peel was accumulated until the end of a run, then weighed and put
batchwise through the finisher to separate recovered peel pulp from the skin
and miscellaneous seeds and fiber. The 0.5 inch clearance used in 1975 when
processing continuously was inadequate with the small batches. Therefore,
a 3/32-in. clearance was used; even so, the 1976 pomace was wetter than in
1975.
SAMPLE LOCATIONS
1975 Stations
Samples of tomato materials were collected at several locations (Fig-
ure 2) in both the commercial and experimental processes during each of
the test runs. These locations were similar for both 1975 and 1976.
Station 1—Peel residuals were sampled at the peel tank preceding the
extractor. Aliquots of approximately 300 ml were collected at the beginning,
during the middle, and toward the end of each test run. A composite sample
was made of these aliquots in 1-quart plastic containers. In all cases,
samples collected at this station were obtained prior to acidification.
Station 2—Recovered pulp samples were collected at the discharge from
the extractor in the same manner described above. When acidification of the
pulp was conducted after extraction, samples collected at this point were
alkaline; when acidification was conducted before extraction, the samples
were acidic.
Station 3—Acidified and heated pulp was sampled from the pulp tank
following the hot break. Aliquots of 400 to 500 ml were collected about
1/4 hour after steady-state conditions were achieved and toward the end of
each run. These aliquots were composited and cooled in 1-quart plastic
18
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containers. These samples were identified as "Sample 3." When additional
test conditions were imposed (such as concentrating, blending, or holding),
additional single samples of approximately one liter were obtained and
identified by an alphabetical suffix (e.g., 3A, 3B, etc.).
Station 4—Recovered pulp was canned at the end of each test run. The
hot pulp was obtained from the pulp tank following the hot break, placed into
211 x 400 unlined cans, sealed and heat processed by immersion in boiling
water (100°C) for 40 minutes. The cans were cooled by immersion in cold
(23°C) water. When additional test conditions were imposed, as described
above, additional cans of material were preserved in a like manner. Each set
of cans was assigned an appropriate code. However, for analytical purposes,
the additional samples were assigned alphabetical suffixes (4A, 4B, etc.).
Station 5—Samples of tomato skin and seeds ejected by the extractor
were collected in plastic bags. Approximately 100 to 200 g of material
were collected at the beginning, during the middle, and toward the end of
each run. These portions were composited for laboratory analysis.
Station 6—Whole tomatoes entering the conventional caustic applicators
(baths) were sampled. About 8 to 12 tomatoes were randomly picked at the
beginning and at the end of each test run. The two portions were composited
in plastic bags for laboratory analysis.
Station 7—Peeled tomatoes exiting the disc peelers were sampled. About
8 to 12 tomatoes were randomly picked from the various units at the beginning
and end of each run; the two portions were composited in plastic bags.
Station 8—Juice discharged from the conventional finishers was col-
lected during the middle and at the end of each run. The 450 to 500 ml
aliquots were composited and cooled in 1-quart plastic containers.
Station 9—Conventionally prepared tomato paste was sampled about 1/2
hour after each test run. About 300 g of material were collected in plastic
bags. When other conventionally prepared tomato products, such as juice or
sauce, was used to blend with the recovered pulp, additional samples were
obtained. The latter materials were identified by an alphabetical suffix.
Appropriate codes were also assigned to cans of these materials.
Station 10—Pomace from the conventional pulpers was collected in plas-
tic bags. Each sample consisted of 100 to 200-g portions which were collec-
ted during the middle and toward the end of each test run.
All uncanned samples were held on ice during the compositing period, as
well as during transport from the test site to the laboratory. Upon delivery
to the laboratory, the samples were immediately placed under refrigeration
(4°C). Analyses were performed as quickly thereafter as practicable.
Samples which were collected for ascorbic acid (Vitamin C) determina-
tions (dichlorophenolindophenol method) were immediately weighed (20 g) and
mixed with a solution of metaphosphoric - glacial acetic acid. The acidified
samples were held on ice until delivery to the laboratory. These samples
19
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were then frozen until analysis could be performed. Samples collected for
0-carotene (Vitamin A) determinations and protein analysis were also iced
until delivery and frozen in the laboratory prior to analysis.
The canned samples were cooled at the test site, transported to the
laboratory, and held under refrigeration (4°C). This precautionary mea-
sure was taken to preclude spoilage, a concern due to the uncertainty of
adequate processing at 100°C.
1976 Stations
The 1976 sample positions corresponded to those in 1975. Recovered
peel pulp was canned as a single strength, acidified pulp, then heat pro-
cessed after sealing. All samples were taken from the pilot line, none
from the cannery. For instance, the fresh, washed tomatoes came from the
pilot sorting belt which corresponded to the 1975 Station 6, and so forth.
Some samples, such as the caustic bath, were from a similar station as in
1975, but of a different character. For instance, the caustic in 1976 had
to be changed between each trial to eliminate prior materials affecting
subsequent tests; therefore, the 1976 caustic was "fresh" and the 1975
caustic was "mellowed", a point which would not show up based on caustic
content. A "water dip" was used to cushion the fall of the tomatoes as they
came off the disc peeler, and served to rinse the tomatoes before they were
elevated into barrels for weighing. Since this was not a typical cannery
bath or flume, samples would not have been representative of a commercial
situation.
ANALYTICAL METHODS
In both years the collected samples were analyzed for parameters con-
sidered most significant for the respective sampling location. Emphasis
was placed on obtaining data relative to the quality of the recovered pulp.
The significance and major parameters evaluated for each sampling location
are identified below. Most of these analyses were conducted on frozen and
canned samples at the NFPA, Berkeley and the WRRC, Albany laboratories.
Fresh material was analyzed in the laboratory trailer at the experimental
site. Field analyses during 1975 were primarily Agtron (M500-A) and Munsell
colors, salt, pH, and alkalinity, carried out on the Incoming peel and acidi-
fied pulp; in 1976, these analyses were NTSS, pH, alkalinity (for acid
requirement), peeling efficiency, lye concentration, and serum viscosity.
The purpose was to provide guidance for the experimental processing
because the Berkeley and Albany laboratory data would not be available until
after the experimental period. Where there was duplication of data from the
field and research labs, the correlation was good. Additional details per-
taining to the analytical procedures may be found in the references cited.
pH—The pH of all samples was measured to determine the relative
acidity or basicity of each. Since the pH of solutions greatly Influences
the resistance of microorganisms to heat, as well as their ability to grow,
the Federal Food and Drug Administration has arbitrarily established pH 4.6
as the value differentiating low-acid products from high-acid commodities.
20
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Thermal processing regulations have been promulgated for low-acid foods (9).
The natural pH of raw tomatoes processed in California normally fall
pH 4.2 and 4.4.
Measurements were made electrometrically by direct insertion of a
combination electrode into fluid sample. The pH of semi-dry pomace/skin
samples was obtained by adding 2 to 3 parts (by weight) of water to 1 part
of sample, stirring, and measuring after equilibrium had-apparently been
attained (about 30 minutes). Whole tomatoes were homogenized prior to pH
measurement.
Total Solids (TS)—Since most commercial tomato products are concentra-
ted to varying degrees, the amount of moisture present in tomato pulp is of
interest. Additionally, the amount of moisture present in tomato pomace
may serve as an index of the operating efficiency of pulpers and finishers
which are used to extract pulp (juice) from crushed tomatoes. Moisture
was determined by drying an appropriate weight of sample, based on an
approximation of the solids percentage in the sample, in a vacuum oven
(29 inches) for 4 hours at 70°C. Total solids were then calculated and
expressed as "percent dry weight" (10). As tabulated, the total solids
data include salt.
Natural Tomato Soluble Solids (NTSS)—Estimation of the total solids and
specific gravity of tomato products may be obtained by measuring the refrac-
tive index (Brix) of the tomato serum (11). Natural tomato soluble solids
are also the basis for establishing United States Standards for Grades of
tomato products. Therefore, refractive index is commonly used by the
industry in quality control. Direct readings at 25°C were taken for most
of the samples collected during the study. Serum from samples containing
higher solids percentages was obtained by centrifugation. All acidified
samples were corrected for salt; results are expressed as "percent sucrose."
Salt (Sodium Chloride)—Salt is a commonly used seasoning for many
tomato products. Since sodium chloride is formed by neutralization of
sodium hydroxide with hydrochloric acid, the quantity of salt in the
recovered tomato pulp was of interest. Total chlorides were measured by
potentiometric titration with silver nitrate and the use of a silver elec-
trode (12). Laboratory results are expressed as "percent salt (sodium
chloride.)".
Alkalinity. Total—Total alkalinity measurements were conducted to
determine the relative quantity of residual caustic (sodium hydroxide)
contained in the collected samples. A 5.0 g sample was titrated with
0.1N H2SO^ to an arbitrarily selected end-point of pH 4.2.
Consistency and Viscosity—The consistency of tomato products is affec-
ted by the amount of and extent of degradation of pectin, as well as the
size, shape and quantity of thixotropic and insoluble materials contained
therein. The United States Standards for Grades of tomato products specify
limits for this parameter. Therefore, consistency measurements were made
with a Bostwick Consistometer; results are expressed in centimeters in 30
seconds (14). Viscosity measurements, performed on free-flow samples, were
21
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made by timing a specified volume through a capillary tube (15). In general
usage, "consistency" is the term for the fluid-flow resistance of viscous
foods, such as tomato pulp, with a relatively great amount of insoluble
solids; "viscosity" is used for those fluids without appreciable insoluble
solids, such as tomato serum.
Samples (chilled, then frozen) were checked for possible pectin enzyme
activity before the hot break. Samples of alkaline peel pulp were acidified
to approximately pH 4.2 either: (a) manually in the field laboratory or
(b) automatically in the process (before the hot-break). Then they were
cooled below 70°F within 5 minutes of acidification, packed in ice for about
3 hours, and stored at 0°F until evaluated for pectin enzyme activity. In
one case the process acidified sample was held, without hot-break, for 90
minutes at 100 to 120°F before chilling and then stored cold in the manner
described above; this hold was to check short term color and microbiological
stability.
The activity of the pectic enzymes in the acidified samples was deter-
mined in 1975 by measuring changes in consistency after mixing the test
samples with a high consistency tomato juice, which served as a pectin sub-
strate. The test sample was added to the substrate at a ratio of 1:10, and
the consistency was measured at 25°C over a period of 1 hour or more by the
efflux-pipet method.
Further serum viscosity tests were made in 1976 by neutralizing the
caustic with acid before peel removal so as to isolate viscosity changes
occurring in the caustic bath from those taking place afterward.
Vitamins—Tomatoes and tomato products are considered to be signifi-
cant sources of Vitamin A (B-carotene) and Vitamin C (ascorbic acid) in a
normal adult daily diet. Both of these nutrients can be degraded through
chemical treatment, heat, and/or oxidation. Since the recovered pulp was
subjected to all three of these conditions, the vitamin content of the final
recovered material was of concern. Vitamin A was determined spectrophotome-
trically; results are expressed as. "International units per 100 g" (16).
(Appendix A).
The initial analysis of Vitamin C (ascorbic acid) was made by the
2,6-dichlorophenolindophenol visual titration method, which is unsuitable
if there are other reducing agents present or if some of the Vitamin C acti-
vity is due to dehydroascorbic acid (25). Inorganic reducing agents are
usually minimal in tomato products but organic reducing substances, collec-
tively termed reductones, are often formed in products which have undergone
extensive heat treatment. Such reductones are formed by the action of alkali
on sugar. An alternative method that avoids interference by inorganic
reducing agents and assays total Vitamin C by including dehydroascorbic acid
is the method of Roe and co-workers (17). This method involves the oxidation
of ascorbic acid to dehydroascorbic acid, subsequent transformation of
dehydroascorbic acid to diketogulonic acid, and coupling of this product with
2,4-dinitrophenylhydrazine under carefully controlled conditions to give
red-colored osazones. A comparison of the color produced in samples and
22
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ascorbic acid standards is used as a means of determining ascorbic acid con-
tent. The absorption of light by the pigment formed is maximum at a range
of 510 to 520 mp. Since any reductones present form osazones that absorb
in the region of 450 to 490 mu and these absorb more intensely than the red
osazone of ascorbic acid (i.e., diketogulonic acid), a more accurate assay
of ascorbic acid in the presence of reductones is obtained by reading absorp-
tion at 540 ran rather than at 510 to 520 my. However, if reductones are
present in large amounts, high estimates of ascorbic acid will nevertheless
be obtained due to the interfering absorption of the reductones; therefore,
a chromatographic separation is required to separate the osazones of ascorbic
acid from those of the reductones before making absorption readings at 520 m\i.
The usual chromatographic separation of osazones by both column and
thin-layer chromatography was modified to a separation by column chromatogra-
phy alone, using a development solvent of acetic acid, ethyl acetate, and
methylene chloride (3:20:97). In all cases, a sample with a known level of
ascorbic acid added was also assayed by chromatographic isolation and color-
metric determination of the osazone at 520 mu.
Peeling Aids—Peeling aid additives are carried out of the caustic baths
by the tomatoes. Residues are removed from the peeled product during the
peel removal and washing/rinsing operations. These residues appear in the
peel residual and in the effluent wash waters whenever the latter operation
is performed. Samples collected from the test system were analyzed for
peeling aids; selected samples from conventional operations served as con-
trols. Concentrations of sodium 2-ethylhexylsulfate and sodium mono- and
di-methyl naphthalene sulfonates in appropriate samples were determined by
a methylene-blue dye transfer method (Appendix B). Fatty-acid peeling aids
were determined by esterification of the fatty acid and quantification by
gas-liquid chromatography (GLC) (Appendix C).
Pesticides—The samples were extracted by the method in the Food and
Drug Administration's Pesticide Analytical Manual (19). The extracts were
cleaned through activated florisil. Toxaphene and thiodan were detected in
their respective florisil eluates by GLC using the electron-capture detector.
Parathion was detected by GLC using the flame photometric phosphorus detec-
tor. All pesticide analyses were performed by Stoner Laboratories, Santa
Clara, California.
Toxaphene is a complex mixture of compounds manufactured by the chlori-
nation of camphene and related compounds. Treatment with base caustic in
the laboratory causes dehydrochlorination which appears during GLC as a shift
to earlier eluting compounds (using methyl or phenyl silicone columns). A
similar shift to earlier eluting compounds can be seen in old toxaphene resi-
dues in environmental soils, and similar shifts were visible in some samples.
By varying the strength of base used during hydrolysis, standards were
synthesized with varying degrees of decomposition (as evidenced by their
shift to shorter retention times). The toxaphene in some of the samples was
like the (Stoner) mildly decomposed standard, and some were like the (Stoner)
strongly decomposed standard.
23
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Mold and Insect Fragments—The Federal Food, Drug, and Cosmetic Act
in Section 402(a)(4) precludes the sale of products which "may have become
contaminated with filth", whether or not such contaminants may pose hazards
to health. "Defect action levels" have been established by the FDA for
natural or unavoidable defects in foods for human use where no health
hazards exist. Mold and insect fragments, resulting from field, transpor-
tation or storage conditions, fall into this category. Since these exist
largely on the surface of the raw product, there was interest whether the
pulp recovered from peel residuals might contain excessively high counts
of these contaminants. Randomly selected canned samples were microscop-
ically examined for mold and insect fragments (20). Mold is reported as
percent of positive microscope fields; insect fragments are reported as
total counts of fragments per 200 g. (Note: defect action levels are
established for Drosophila fly eggs and/or larvae per 100 g).
Bacterial Counts—Tomato pulp samples were taken before and after
the hot break, and checked for mesophilic (30°C incubation), thermophilic
(50°C incubation), and total plate counts (30°C incubation). Plating was
on glucose-tryptone agar. Vegetative cells (mesophilic) are more heat
labile than the spores (thermophilic) so comparing the counts can indicate
survival and reinoculation, equipment cleanliness and heat processing
adequacy.
Quality Factors—The United States Standards for Grades of Canned
Tomato Puree (Tomato Pulp) establishes the criteria classifying the quality
of canned product (21). Factors for which scores are assigned are color
and defects (dark specks, seeds, tomato peel, and other extraneous mate-
rials); non-scored factors are subjective evaluation of flavor and odor.
The texture of graded samples are also routinely noted.
The above quality factors were evaluated by inspectors of the Fruit
and Vegetable Quality Division, Food Safety and Quality Service, U.S.
Department of Agriculture, Stockton, California. Color scores were deter-
mined by the specified Munsell color disc comparison procedure or by the
use of a Hunter colorimeter. Color and defect scores are based on a maximum
of 50 points for each factor. Canned recovered pulp samples were submitted
for quality evaluation. These results were of primary concern since they
would largely determine the commercial acceptability and utility of the
recovered materials. In the lab trailer, color was measured with the Agtron
and Munsell instruments during 1975 but not during 1976.
Nitrogen and Amino Acids—Tomato pulp samples were analyzed for total
nitrogen content and basic amino acids before and/or after centrifugation
into soluble and insoluble fractions. The two fractions were obtained by
centrifuging samples at 35000 G for 10 minutes. The Insoluble solids were
washed twice by re-suspending in distilled water to about 1.5 times the
original volume and centrifuging. The washes were combined with the soluble
fraction, and the solubles were concentrated by vacuum distillation at
45-50°C to near their original volume. In all cases the assay results for
a fraction (soluble or insoluble) were expressed on the basis of the whole
sample weight equivalent. The total nitrogen content of each sample was
determined by Kjeldahl procedure (22). On the basis of the Kjeldahl results,
24
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samples of 0.8 to 3.2 mg N were hydrolyzed in 6-N HC1 (33). After the HC1
was thoroughly removed by vacuum distillation at 45 - 50°C, the sample was
concentrated to dryness with a rotary evaporator and suspended in a measured
volume of pH 2.2 buffer. Then the sample was filtered and the protein hydro-
lysate was analyzed for amino acids using an automatic amino acid analyzer
(Beckman Model 120, Phoenix Model K8000 B, or Durrum D-500) (23).
25
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SECTION 6
RESULTS AND DISCUSSION
General
The results from 1975-76 showed that tomato pulp recovered from caustic
peelings has food potential. Product grades varied according to the process-
ing method, and these results showed the necessity of processing the tomato
pulp with care so as to achieve its full potential. Experimentation spanned
two years. In 1975, tomato peel was taken directly from a commercial caustic
peeling operation; this recovered pulp was characterized as to its color,
grade, and conformity to the Standards of Identity. In 1976 process changes
were made, then tried on a pilot peeling line to minimize the peeling-aid
residuals found in the 1975 recovered pulps.
While the 1975 results (Table 1) showed there is food potential in
recovered pulp, there was one major detraction—the peeling aid residue at
150-450 ppm. Of the currently used commercial peeling aids (sodium 2-
ethylhexyl sulfate, sodium mono- and di-methyl naphthalene sulfonates, or
fatty-acid mixtures containing predominately odd-numbered carbons), none
seem suitable for clearance as food additives. Even if an additive-grade
peeling aid were currently available, the 150-450 ppm residue is large
enough to raise questions about declaring it on the product label as an
additive.
While it is possible to peel tomatoes without a peeling aid, it is
generally acknowledged that higher caustic concentration or increased tem-
perature is required; these lead to higher peel losses, and as a result,
the peeled tomato quality suffers since the vascular veins become more
pronounced. The peeling aid residue level possibly could be reduced to
less than that found in 1975, but it was considered improbable to reduce
the residue to near zero once a peeling aid was introduced into the caustic
peeling system. Therefore, a modified caustic peeling was developed in
1976 by using food grade chemicals as peeling aids and applying them as
a precaustic treatment instead of adding directly to the caustic bath.
In normal cannery operations, the juice and pulp supplies are inter-
connected so that these materials can be shunted between the different
sources and utilization points to satisfy changing production requirements.
Therefore, in actual cannery practice recovered peel pulp could be combined
with juice and macerate from other sources before processing into standard
products such as tomato sauce, catsup, fill juice for whole-canned tomatoes,
or other salted products. During acidification and possibly at the rubber-
disc peel removal point, a small amount of water might be incorporated into
26
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TABLE 1. SUMMARY OF TYPICAL 1975-1976 RECOVERED PEEL PULPS
Typical Single-Strength Tomato Pulps
Item
1975
1976
Conventional
Processing
(a)
Recovery of peel %w/w
NTSS, (natural tomato soluble
solids), %w/w
Salt, (sodium chloride), g/100 gm
Total solids, (salt free), %w/w
Vitamin A, (beta-carotene),
I.U./100 gm
Vitamin C, (ascorbic acid),
mg/100 gm
Color grade, (per puree std)
Flavor grade, (per puree std)
Peeling-aid residue, pulp
ppm (c)
Insecticide residue, pulp product,
toxaphene ppm (f)
Insecticide residue, skin waste,
toxaphene ppm
96.7%
5.3
3.-
5.6
665
95%
5.2
1.1
5.9
(b)
nil
nil
A-C A
C A-C
150 - 450 0 - 30
0.4
5-60 34
trace
n/a
5.4
0.08
5.71
516
10.7
A
A
0 (d)
trace
7 (e)
trace positive amount less than 0.08 ppm.
n/a not applicable (no current commercial recovery).
(a) industry 4-yr averages, except salt which is 2-yr average.
(b) not analyzed.
(c) sodium 2-ethylhexyl sulfate in 1975, octanoic acid in 1976.
(d) no peeling aid used in conventional juicing/pulping.
(e) pomace from juicing, seeds with proportionally less skin than in
peel-pulp recovery.
(f) tolerance is 7.0 ppm in canned and fresh tomatoes
27
-------
the peel. This water must be removed, either through subsequent concentra-
tion such as for tomato sauce, or during the evaporation that occurs from
holding tanks. This water could be removed either before or after combining
with other pulps. There seems little processing justification for keeping
recovered pulp isolated for use in a special product since there is an
insufficient quantity of recoverable pulp to maintain a separate proces-
sing line.
The various process and product aspects are discussed below, including
the unit operations, recovered pulp characteristics, and economic and regula-
tory considerations.
Washing and Sorting—Peel pulp recovered during the 1975 season from
the typical cannery peeling operation (Tillie Lewis Foods, Plant W) had low
mold, insect fragment, and bacterial counts that were well within regulatory
tolerances. This showed that the cannery had an excellent washing and sort-
ing system consisting of counter-current water flow and fine sprays, all
with a relatively low total water usage of 750 gal/ton of tomatoes for the
entire plant. Tomato washing consisted of the primary dump tanks, a secon-
dary flume, a third flume, and a final fresh-water rinse as the tomatoes
passed over roller conveyors. Water was chlorinated to 5 ppm. In 1976
tomatoes were received before commercial processing and washed in the pilot
systems; the final rinse over rubber-discs corresponded to the previous
year's use of rollers. Sorting in 1976 was varied from zero to 20% of the
peeled tomato weight; the higher sorting was necessary when the California
State Grade Certificate showed 3% mold. While the Grade Certificate is an
indication of mold on in-coming raw product, the tomatoes were graded up to
24 hours prior, so the actual mold count could have been higher at the time
of experimental processing. An alternative to hand sorting is the use of
high-pressure water sprays (70-120 psig) as practiced for a number of years
by most canners to remove broken and moldy tomatoes.
Washing and sorting methods to remove contaminants from raw commodities
vary between canneries. A guide to the tolerances for the so called "natural
or unavoidable defects" in tomato products, such as mold, rot, insects,
etc., is published periodically by FDA (30).
Peeling Aids—A peeling aid (also called surfactant, surface-active
agent, wetting agent) is used by all commercial canneries in the caustic
applicator (bath). The purpose of the peeling aid is to promote uniform
peel removal. Without it, yellow shouldered areas on the tomato tend not
to be peeled. While a caustic peeling solution alone may peel satisfac-
torily on occasion, there are times when changing the temperature,
immersion time, or caustic strength is not sufficient to effect quality
peeling. Particularly at such times, the addition of a peeling aid can
improve peeling in a rather empirical manner. If the tomato is given a
prolonged submergence in the caustic or if the caustic concentration is
increased, the peeling losses rise and the vascular (white) veins of the
tomato become more prominent. The result is a poorer quality product and
greater loss. These comments pertain more to the relatively "tough skinned"
VF-145 processing tomato variety which accounts for perhaps 60% of the
processing tomatoes grown in the U.S.A. There are various materials
28
-------
permitted as washing or peeling aids (26), but none of these are permitted
as additives in tomato products. Their use is permitted with the provision
that after leaving the caustic applicator, the tomatoes will be washed with
water, and there will be negligible peeling aid remaining on the whole
tomato. The permitted aids are water soluble; hence, water is the conven-
tional means of removal.
Sodium 2-ethylhexyl sulfate (Emersal 6465; Emery Industries Co.,
Cincinnati, Ohio) was used at the cannery during 1975. Subsequent experimen-
tation showed that sodium mono- and di-methyl naphthalene sulfonates and fatty
acids responded similarly with respect to residues in the recovered pulp.
The sensitivity of the analytical method for sodium 2-ethylhexyl sulfate is
about 25-50 ppm because natural tomato constituents interfere slightly with
the analysis. The ratio of peeling aid to sodium in the caustic applicator
was about the same as that found in the recovered peel pulp. The levels of
peeling aid in the peel pulp were usually in the range of 150-450 ppm; such
levels are not acceptable for tomato products. No peeling aid residue was
found on peeled whole tomatoes after peel removal. The detection level was
about 25 ppm for sodium 2-ethylhexyl sulfate and 1 ppm for fatty acids.
During the spring 1976 laboratory peeling study, the C& and Cg saturated,
monocarboxylic fatty acids were the most effective peeling-aids. Octanoic
(caprylic) acid was the principal one used because it was as effective and
less volatile than hexanoic acid. It is commercially available in a food
grade (27) at a price competitive with peeling aids currently used in
commercial tomato peeling. The 150°F pretreatment was as effective, or more
so, as using the peeling aid directly in the caustic applicator. For easy-
peeling tomatoes, such as those suitable for steam peeling, it was possible
to peel without caustic by using a 1 to 2 min. immersion in a 150°F aqueous
bath containing 0.2% w/w octanoic acid. While it may be convenient to apply
the peeling aid with caustic, there is no inherent reason why it requires
the same application temperature, pH, and immersion time as the caustic.
Peeling aids are commonly referred to as "wetting agents", but the most
effective ones may do more than reduce the interfacial tension between the
tomato surface and the caustic. Some wetting agents, such as sodium oleate
or sodium lauryl sulfate, will show high-wetting improvement, but they will
have little effect on peeling whether applied as a pretreatment or directly
in the caustic bath. Others, such as sodium 2-ethylhexyl sulfate and sodium
mono- and di-methyl naphthalene sulfonates, perform better when applied
directly in the caustic bath than when used as a pretreatment. The most
effective peeling aids appear to react chemically and (or) to disrupt the
cell structure and allow enzyme action. This is illustrated by peeling
tomatoes with only an acidic aqueous solution of octanoic acid at 150°F;
this is discussed further under "Carboxylic Acid Peeling".
Octanoic acid does have a characteristic aroma (rancid, cheesy), and
is used at up to about 400 ppm in synthetic blue cheese. In single strength
tomato juice, less than 10 ppm is indistinguishable from plain tomato juice.
The flavor threshold is about 20 ppm, and 50 ppm has a flavor identifiable
as a fatty acid. This threshold would be higher in spiced sauces. This
20 ppm threshold is significantly higher than the 10 ppm proposed level for
29
-------
general use in the GRAS affirmation under good manufacturing practice as
a direct food ingredient as published in the June 1977 Federal Register
(28). People differ in their threshold sensitivity to caprylic acid, but
in another study, 19 ppm was found to be the odor threshold for a normal
person to caprylic acid in buffered water at pH 4.8 (32).
Carboxylic Acid Peeling—The carboxylic acid peeling was accomplished
with a 150°F aqueous solution containing 0.2% octanoic (caprylic) acid at
about pH 3.6 and with a one to three minute immersion. This completely
peeled the tomato varieties Tropic, Walter, Roma-VF, and VF-145-21-4 (con-
tains a uniform-ripening gene). For the VF-145B-7879, UC-134, 198, and 13L,
which are typical California processing tomatoes, the skin was loosened and
peeling aided, but a subsequent caustic application was generally needed.
The peeling loss averaged about 5% with octanoic acid as compared to 12%
for caustic using commercial peeling aids. The difference was visually
dramatic because caustic peel was red due to the adhering pulp, whereas the
octanoic acid peel was a translucent, pale yellow because no pulp adhered.
Other secondary treatments than caustic were atmospheric steam (30 sec.)
and 900°F superheated steam (7 sec.). Both steam treatments provide addi-
tional peel loosening capability, particularly the 900°F steam which splits
the skin and makes peel removal easier.
While octanoic acid performed best among the candidates as a peeling
agent, all the CA to Cg saturated monocarboxylic acids showed the most promise.
Time was limited and an extensive pursuit of the ideal peeling agent or aid
was not feasible. Octanoic acid occurs naturally in coconut oil and blue
cheese, is readily available commercially in a food grade, and is priced
similar to the currently used peeling aids. A food-grade peeling aid should
be biologically metabolized in predictable fashion by both humans and animals
or microorganisms associated with man, and octanoic acid fits this require-
ment. This is currently being considered in a proposed affirmation of the
GRAS status of caprylic acid (28). With the wide-spread use of steam peeling
in Europe, the carboxylic-acid peeling seems to be potentially competitive
or an aid to steam peeling because of peeling varieties such as the San
Marzano and Roma (31). The use of octanoic acid not only could improve peel
removal, but it could reduce the duration of steam exposure and heat which
softens the tomatoes unduly and increases peel loss.
Peeling Aid Pretreatment—During the 1976 tests pretreatment tempera-
tures were varied from 75°F to 210°F. Initially, 150°F was chosen so as to
be below enzyme-inactivation temperature. Experimentation showed that below
about 140°F the peeling aid pretreatment was less effective or required long
immersion, such as up to 10 minutes. Above about 170°F, even with a short
dip, the tomatoes became increasingly soft and the peel loss increased.
Overall, 150°F was best, with the 140°F to 160°F range being practical. Even
a 150°F water (100%) pretreatment usually showed some peeling improvement,
but use of a peeling aid was definitely better.
When a pretreatment is used, fatty acids offer a potential advantage
over sodium 2-ethylhexyl sulfate (SEHS) and sodium mono- and di-methyl
naphthlene sulfonates (SNS) because they tend to loosen the tomato skin
while in an aqueous solution as discussed under "Carboxylic Acid Peeling".
30
-------
The limited data and visual observation indicate better peeling when hexanoic
(caproic) and octanoic (caprylic) acids were used as a pretreatment than when
used directly in the caustic applicator. When the peeling aid is used direc-
tly in the caustic applicator, then all four of these peeling aids were about
equally effective on an active ingredients basis. As commercially sold, the
fatty acid peeling aids contain 100% active ingredients, and the SEHS and SNS
contain 50% as these latter ones are distributed as water solutions. Although
all peeling aids were used singularly in this experimentation, mixtures of
fatty acids and other chemicals may offer additional peeling benefits, and
further study would be beneficial. One example is that octanoic acid has a
limited solubility of 0.12% in water at 150°F, and this level can be increased
by the addition of acetic acid which will act as a co-solvent. The object
of this work was to find a food-grade peeling aid and application method to
obtain the full benefits of a peeling aid and to minimize residuals in the
recovered pulp. Hence, the data were not necessarily of a nature to differ-
entiate relative effectiveness of currently used peeling aids.
Modified-Caustic Peeling—The term "Modified Caustic Peeling" is used
to indicate the tomato pretreatment with a peeling aid prior to the caustic
applicator instead of the standard commercial practice of putting peeling
aid in the caustic bath.
The 1976 cannery pilot peeling was mostly with the tomato variety
UC-134 because it was usually the only tomato available at the cannery.
This variety is also considered at least as difficult to peel as the more
prevalent VF-145-7879. When the VF-145, 198, and 13L were peeled, they
responded similarly to that of the UC-134 with respect to peeling aid pre-
treatment efficiency and residue in the recovered pulps.
When comparing peeling methods with a pilot line, it is possible to
simulate commercial conditions but nearly impossible to simulate all aspects
of the actual scale. Tomatoes change with each truck load and even within
the load. Duplicating caustic solution is more than similar temperature and
caustic concentrations because the usual cannery solution takes about one
week to reach equilibrium between caustic and disintegrated tomato solids.
Either the industry collectively, or each processor individually, will need
to consider long term process factors such as: (a) pretreatment bath stabil-
ity and replenishment frequency, (b) peeling aid carryover to the caustic bath
and the peeling aid (octanoic acid) level in the recovered pulp, and (c)
safety features such as the need of flow diversion for off-control material.
Peel Removal—Any peel removal system can be used to supply a pulp
recovery system if the recovered pulp is not diluted with water. Water
sprays may exist on peel removal systems either to provide lubrication,
rinse peel from the equipment, or to remove peel from the tomato. If the
water added to the peel is incidental, such as 1% of the peel weight, then
this amount probably would not be significant if it is removed during fur-
ther processing or by normal evaporation from holding tanks. Both the
FMC PR-20 Tomato Peel Remover and the Magnuson Model C Peel Scrubbers sup-
plied peel for the 1975 recovery. In the FMC remover, the peel is removed
in two stages; the first stage is a horizontal bed of rubber discs, and the
second is a flat bed of "pinch" rollers. In this case, peel was taken only
31
-------
from the rubber disc section because the roll section had water sprays.
In the Magnuson, the peel comes off in a one-stage rotary cage, disc unit.
Both machines can provide recoverable peel in a production situation, and
the choice between these or other machines would seem to be a matter of
individual preference.
A flat-bed disc unit was used in the 1976 pilot peeling tests. The
peeler was quite sensitive to the degree of loading because peel removal
depends not only on the discs contacting the tomato but also on the inter-
tomato contact and rubbing. With a 1-ft wide pilot peeler loaded at 1-t/hr
of tomatoes, there was not sufficient inter-tomato contact for optimum peel
removal. An 8-in. width would have been more appropriate, but the width
would have introduced another variable and was therefore kept at a constant
12-in. for all trials. When the flat-bed type is used commercially, it is
often used in combination with "pinch" rolls as on the FMC unit; the pilot
system would have benefited from such "pinch" rolls.
Peel Flow—In 1975 the equipment was initially operated at 20-30 gpm,
which was the full flow coming from the cannery. Although the full flow
could be handled by the experimental equipment units, surges in the flow
taxed the heating capacity of the hot break to the limit of the available
steam pressure (45 psig). Also, overflows from the caustic applicators were
discharged into the peel troughs, creating an acid demand that exceeded the
acid flow capacity; the caustic overflow was a local condition which could
not be modified at the time. Subsequently, peel flow into the peel tank
was controlled to about 15 gpm by installing a 1-inch angle valve at the
peel tank. This valve controlled the peel flow reasonably well, reduced
the effect of the caustic overflow, and provided more stable heating and
pH control. However, tomato skin occasionally clogged the valve port.
These flow stoppages were corrected by installing a positive-displacement
pump (Waukesha 55 DO, 130-520 rpm variable-speed drive, Waukesha Foundry Co.,
Waukesha, Wisconsin) to meter in the peel material. Later, the caustic
carryover into the peel rose to the equivalent of 3% salt; to avoid exces-
sive acid consumption, the peel flow was reduced to about 10 gpm.
The 1976 system peel dropped from the rubber discs onto an underlaying
pan. This peel was then manually scraped into the acidification container
about every 4 to 8 minutes. Peel flow was typically 0.4 gpm. The times from
tomato immersion in the caustic applicator to peel removal, and to acidifi-
cation were similar to 1975. The 1976 operation simulated a normal peeling
operation and did not have to contend with the unreasonable caustic variations
experienced in 1975. The contrast between these two years served to emphasize
the production control required.
Peel Alkalinity—The daily (1975) measured acid use is shown in Table 2,
and laboratory pH adjusted alkaline (caustic) pulps are shown in Figure 8.
This provides guidance for estimating acid requirements which are expressed
as pounds of acid used per pound of tomato solids (w/w). If the caustic
applicators had not been piped to overflow into the peel, the salt in the
recovered acidified peel pulp would have been about 1.1% as in 1976. The
present trend among processors is to recycle any overflow as makeup to the
32
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PEEL FROM 1975
CANNERY PEELING OPERATION,
INITIALLY AT pH 12.8
COMMERCIALLY CANNED
TOMATO PUREE
INITALLY ADJUSTED
TO pH 12.5
14
Figure 8. Acid required to reduce pH of caustic peel and pulp.
33
-------
applicators after separating suspended solids, and to empty the caustic
applicators less frequently than once per week.
Acidification—Early and rapid acidification is necessary because the
tomato character is more stable at the natural pH 4.2 than at pH 11-12. At
the high pH both color and flavor deteriorate with time and temperature,
though microbiological growth is inhibited. Once acidification commences,
a rapid decrease, in less than 10 seconds, from pH 11 to 4.2 is necessary
because an off odor was sometimes detected when the acidification paused
at pH 6-10 for several minutes.
Acidification time for the incoming peel was estimated to be 5-10
seconds to reach pH 4.2 in the peel tank, and 30 seconds when acidification
was in the hot break vessel. If the peel was allowed to stand between
approximately pH 6 to 10 for about 30 minutes, particularly above 100°F, off
odor (sulfury) was pronounced; the odor seemed most objectionable at about
pH 9. Color increasingly darkened from pH 10 down to about pH 7, then
improved below pH 5. Below pH 5, the color was good down to pH 2. Peel
received and held at pH 12 generally had a better color than if reduced
and held at pH 7-10.
Acidification can be performed either before or after the skin is
separated from the pulp. Since pulp recovery was 96% or better, there was
little reason to be concerned with acid economy by acidifying after the
skin removal, although both were tried. This leaves the processor the
freedom of ultimately separating pulp and seeds either in an individual
machine or combining this separation with other pulping operations in the
cannery. For general pH control, ease of operation, and product quality,
acidifying in the peel tank was best. The tank configuration shown in the
diagram (Figure 4) was suitable for pH control at flows up to 20 gpm.
There is a definite preference for acidifying the pulp before heating
since pulp held in the alkaline state is more susceptible to thermal dis-
coloration (browning). There was no significant recovery difference in
product or extractor operation whether the peel was extracted in an alka-
line or acid condition.
Salt (Sodium Chloride)—Acidification of the 1976 caustic peel resulted
in about 1.1% salt in the recovered pulp (Table 6). This salt content is
similar to that found in tomato sauces. Raw whole (unsalted) tomatoes contain
0.08% w/w salt; canned peeled whole tomatoes, 0.4%; canned tomato juice, up
to 0.8%; catsup, 2.7%; and special sauces, such as chili, cocktail, and pizza,
up to 3% salt.
The amount of salt is a reflection of the caustic in the peel. As pre-
viously explained in this report, the (high) 3% salt in 1975 (Table 2) was
a unique, atypical condition due to the caustic bath overflowing into the
peel. Therefore, it is the nominal 1.1% salt which needs to be considered
when utilizing recovered pulp both as a source of pulp and salt. To control
the salt content in the final product, the salt from acidification can be
managed in a number of ways, two of which are: (1) the salt content can be
continuously monitored (analyzed) through either automatic or manual titration
34
-------
for chloride or by selective ion electrode for sodium, and when blended with
conventional unsalted pulp material, the salt normally added to products can
be adjusted accordingly, or (2) the recovered pulp can be blended with con-
ventional unsalted pulp so that the salt contribution will be insignificant,
and the regular salting procedure can be used.
Pulp Extraction—The basic pulp extraction information was obtained
in 1975 on a continuous flow basis at rates which would be similar to a
TABLE 2. ACIDIFICATION DATA (1975)
Date
(1975)
Sep 03
05
08
09
11
16
17
am 19
pm 19
22
am 23
pm 23
24
25
26
29
30
Oct 01
02
03
07
am 08
pm 08
14
15
16
Avg
Acidifying
period
(minutes)
180
90
180
120
237
105
—
135
100
90
114
90
120
222
120
150
225
126
190
228
153
114
72
205
115
51
Peel pulp
flow
(gpm)
__
—
—
—
—
10.0
—
12.8
—
10.6
10.6
—
10.0
11.4
11.2
10.6
11.3
10.7
—
11.3
—
10.5
—
10.4
10.5
10.8
Caustic
Application
(% w/w NaOH)
(a)
20.
30.
6.9
16.7
15.5
16.7
17.5
9.6
10.
8.
8.
7.9
7.7
7.9
7.7
10.1
8.7
8.6
12.
7.9
6.
8.7
9.1
14.5
6.9
11.
11.3
Acid Used
g 100% HC1
g tomato solids
(b)
0.19
0.15
0.22
0.17
0.30
0.—
—
0.34
0.21
0.42
0.34
0.32
0.39
0.41
0.34
0.25
0.27
0.30
0.23
0.29
0.41
0.33
0.28
0.15
0.46
0.51
0.30
Salt in
Peel pulp
(% NaCl)
— —
—
1.8
1.9
5.4
—
2.6
3.3
2.6
3.3
3.4
3.0
3.5
3.7
3.0
3.0
3.4
2.6
2.9
5.1
4.4
3.3
2.7
1.7
3.9
—
3.2
(a) Average of all caustic applicators in operation (normally 3).
(b) To bring pulp to pH 4.2.
35
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commercial operation (Table 3). In 1976 the quantities were too small so
extraction was on a batch basis and therefore the data were inappropriate
for evaluation of yields. In 1975 with the Extractor (FMC Model 50; FMC
Corporation, San Jose, California) positioned as shown in Figures 2 and 3,
the best pulp recovery and skin extraction was obtained with a 0.033-in.
screen and 0.5-in. paddle-screen clearance. Larger screen sizes (0.060 and
0.125-in.) and small clearance (0.187-in.) allowed too many skin particles
and seed fragments from broken tomatoes to pass through the screen and remain
with the pulp. Within the 1975 conditions, recoveries greater than about
98% had visually obvious skin and seeds going through the screen instead
of being separated from the pulp. This 0.033-inch screen is typical of many
cannery operations. Normal recovery with these settings averaged 96.8% on
a wet basis (82.7% dry-solids basis).
The 0.5-in. clearance was necessary because closer clearances, such as
the common 0.05-in. cannery practice, ground the skin and incorporated it
into the pulp. Caustic action had already loosened the tomato cells so a
wider clearance was necessary. Skin and seed fragments are undesirable be-
cause they are graded as physical defects in products; also, the waxy skin
layer carries the insecticide since the insecticides are fat soluble. Thus,
rejecting the skin is important both as a grade physical defect and as an
insecticide residue control for products. The 1975 regulatory tolerance for
toxaphene was 7.0 ppm. Typically, the recovered pulp contained 0.4 ppm
toxaphene and the skin waste had 5-60 ppm.
To elaborate on the paddle-screen clearances, 0.5-in. and 0.19-in.
were used. Pulp recovery was about 96% on a wet basis with the 0.5-in.
and 99% with the 0.19-in. The 99% recovery occurred because the skin was
comminuted and passed through the screen with the pulp. At no time during
the trials was there any tendency for the screen to become clogged at
either clearance. The extractor waste-outlet gate was open at all times
to minimize the back pressure on the waste and allow it to pass through
without restriction. The 0.5-in. clearance has the added advantage of
greater machine life due to much less machine vibration and less pressure
on the screen.
A 750 rpm extractor speed was used throughout 1975. This is a standard
speed for the machine, normally giving good equipment life, and with a 96.8%
average pulp recovery, there was no need to experiment with various speeds
which would have detracted from more important experimentation.
Vacuum Evaporation—In 1975 four 1,000 gal batches of pulp were con-
centrated; three were recovered peel pulp and the fourth was conventional
cannery juice. The first trial on recovered pulp used a 200°F heating
temperature in the evaporator coils and a 15-in Hg vacuum; this was too high
a temperature and darkened the pulp excessively. The other three runs used
an 180°F temperature and 20—inch Hg vacuum and gave improved color. Even
lower temperatures should be considered because the acidified, recovered
peel is more apt to darken on exposure to heat than is the conventional
juice. During 1976 recovered pulp was not vacuum concentrated because it
was felt that there was adequate information from the prior year.
36
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TABLE 3. SUMMARY OF 1975 PROCESSING CONDITIONS AND SOLIDS RECOVERY
u>
Date
(1975)
9 /3am
9/5am
9/8am
pm
9/9am
9/llam
am
pm
9/16pm
9/17
9/19am
pm
9 /22pm
9 /23am
pm
9/24am
9/25am
9/26pm
9/29am
9 /30am
Peeler
NaOH
(% w/w)
^_
—
—
—
—
—
—
—
9.98
—
12.85
12.85
10.6
10.6
10.6
9.97
11.40
11.17
10.63
11.27
PA
(ppm)
(a)
^
—
—
—
—
1780
1780
1780
1780
—
993
—
—
—
1137
977
1535
1280
1206
1510
Peel
Flow
Rate
(gpm)
20.0
30.0
5.45
8.33
16.67
16.7
—
14.3
16.7
17.5
9.6
10.0
8.0
8.0
7.9
7.7
7.9
7.7
10.1
8.7
Solids Recovery
Pulp Extractor
Acid.
Point
(b)
HB(e)
HB
HB
HB
HB
HB
HB
HB
HB
HB
PT(f)
PT
PT
PT
HB
HB
PT
PT
HB
PT
Screen
Size
(inch)
0.125
0.125
0.125
0.125
0.125
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.033
0.033
0.033
0.033
0.033
0.033
0.033
Clear
(inch)
(c)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.187
0.187
0.187
0.187
0.5
0.5
0.5
0.5
0.5
0.187
0.187
0.5
Temperature, (F)
Inc. Hot
Peel Break
(d)
-._
—
—
—
—
—
—
123
122
120
120
129
127
127
131
136
121
120
117
130
__
—
—
—
—
200
198
200
198
195
200
200
201
200
199
201
199
200
195
200
Wet
Basis
(%)
96.7
—
98.7
98.1
97.3
97.4
97.1
97.5
98.9
95.7
99.4
99.1
97.4
97.1
96.5
97.1
98.7
98.9
98.8
—
Dry
Basis
(%)
85.9
—
91.6
90.4
88.6
85.2
83.9
87.3
94.6
82.2
93.9
91.7
87.0
81.8
69.1
85.0
91.9
88.3
90.1
—
(continued)
-------
TABLE 3. (continued)
U)
oo
Date Peeler
(1975) NaOH
(% w/w)
10/lam 10.67
10/2am —
10/3am 11.33
10/7am
10/8am 10.48
pm 10.48
10/14am 10.44
am 10.44
10/15am 10.51
10/16am 10.80
PA
(ppm)
(a)
1133
1492
1640
960
1262
1283
1465
1465
1058
1275
Average, of all trials
Average, for trials with
Peel
Flow
Rate
(gpm)
8.6
11.3
7.9
6.0
8.7
9.1
12.3
16.6
6.9
11.0
0.033-inch
Solids Recovery
Pulp Extractor
Acid.
Point
(b)
PT(f)
PT
PT
PT
PT
HB(e)
PT
PT
PT
PT
screen
Screen
Size
(inch)
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
and 0.5-inch
Clear
(inch)
(c)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
clearance
Temperature, (F)
Inc.
Peel
(d)
132
—
140
141
130
126
112
113
138
137
Hot
Break
200
194
201
127
200
198
193
199
131
137
Wet
Basis
(%)
96.4
96.4
97.1
96.7
96.9
96.8
95.7
96.0
96.6
97.4
96.8
Dry
Basis
(%)
82.5
82.3
84.6
82.4
85.0
—
82.1
83.3
82.6
85.9
82.7
(a) PA = Peeling aid, sodium 2-ethylhexyl sulfate
(b) Acidification point
(c) Paddle-screen clearance
(d) Incoming
(e) Hot break
(f) PT = Peel tank
-------
Prior to the 1975 cannery experiments, laboratory experimentation was
undertaken to determine if the color darkening, due to high alkaline condi-
tions or heat, occurred in the tomato pigment, the non-serum solids, or in
the serum. In both cases, darkening was in the serum. Separations were made
of these three fractions by centrifuging and solvent extractions , and the
fractions were cycled from pH 4.2 to 11, down to pH 2, and returned to pH
4.2. They were observed visually for significant changes. The pigment
fractions (lycopene and carotenoids) and solids fractions had only slight
color changes. The serum fractions had substantial darkening at pH levels
above 8. This darkening was semi-reversible (perhaps 95%), but with each
alkaline cycle (more severe and not commercially typical) the serum fractions
became progressively darker. Results were similar whether whole pulp or
fractions were cycled.
Unit Operation Times
An early choice was faced on experimental equipment location. Either
it could be placed inside the cannery adjacent to the peel removal or out-
side. Each had an advantage. If inside, the time between caustic applica-
tion and acidification could be reduced perhaps by three minutes, but there
was not sufficient space available to locate all the equipment together,
and the experimental flexibility would have been drastically reduced and
control impaired. With the equipment outside, full flexibility in utili-
zing the experimental equipment was retained. Subsequent experimentation
in 1975-76 indicated that even acidifying the peel directly out of the caus-
tic applicator did not appreciably change the product over that obtained from
the 1976 modified caustic peeling line.
Time increments for each unit operation are shown in Table 4 for the
peel recovery performed in 1975 at the cannery. A similar time sequence
was followed in 1976. Ideally, the time exposure to the caustic should be
zero to minimize potential flavor and color changes. On a practical basis,
immersion in the caustic is necessary for peeling, and it is in this immer-
sion that the principal changes and conditioning occur.
When the peel was received at 110°F, the color was virtually the same as
at the time of peel removal; peel received at 140°F was appreciably darker,
such as when the caustic applicator solution overflowed into the peel. The
30°F temperature increase, rather than the higher caustic content, was proba-
bly the predominant cause of the darkening. As discussed under vacuum
evaporation, acidified recovered peel pulp is more sensitive to thermal
darkening than conventional juice. This displays the importance of control-
ling the process throughout, not just taking any peel and "throwing" in acid.
The time between the peel removal and acidification (about 4.4 minutes)
could be shortened, but there was not sufficient indication that a shorter
time would improve quality appreciably. In 1976 tomatoes were taken directly
from the caustic applicator and quickly plunged in a mild hydrochloric acid
solution to "immediately" acidify the tomato peel; then the peel was removed
by hand and the pulp judged for pectin content, consistency, enzyme activity,
and color. There was no major difference between the pulp from this "instan-
taneous" acidification and pulp that was held at pH 11 for 5-10 minutes at
39
-------
100-110°F. If there is a choice, the quicker acidification is preferred as
it reduces potential adverse changes in color and flavor.
Product Color, Flavor and Vitamins—Product color and flavor differed
between 1975 and 1976, illustrating how the peeling operation and recovery
techniques affect the recovered pulp. As stated before, when the caustic
applicator overflowed, the recovered pulp darkened, had poor flavor, and
2 to 3 times the normal salt content. But even under this very adverse,
atypical condition, the color and flavor could be a food grade, albeit at
times a standard Grade C rather than Grade A.
TABLE 4. UNIT OPERATIONS TIMES - 1975
Operation
Lye application
Peel Removal
Peel Conveyor
Peel Pump and Pipe
Peel Tank (d)
Extractor
Hot Break
Pulp Tank
Canning
Heat Processing
Cooling
Equipment
(a)
C
C
C
C
E
E
E
E
E
E
E
Time
(minutes)
Nominal
Temperature
Increment Total (°F)
(b)
0.5
0.5
0.6
3.8
5.0
0.5
25.0
0.8
10.0
35.0
30.0
0.5
1.0
1.6
5.4
10.4
10.9
35.9
36.7
46.7
81.7
111.7
210
200
180
180-110 (c)
120
110
200
200
185
212
90
(a) C - cannery system, E - Experimental system
(b) After entering caustic applicator
(c) Peel cooled as pumped through 200 ft pipe.
(d) Acidification to pH 4.2 about 0.1 minute after entry into peel
tank, or about 5.5 minutes after tomato entered caustic applicator.
40
-------
As shown in Table 1, the Vitamin A was about the same in the canned peel
pulp as in the processed conventional pulp. Beta-carotene is quite stable,
and since the outer surface (peel) of the tomato is richer than the whole
tomato in this provitamin, the recovered pulp had a higher carotene value
than conventional tomato pulp.
Ascorbic acid is so easily decreased in the presence of hot caustic that
it was not present in pulps from either year (Table 1). Samples of recovered
peel pulp were originally analyzed for ascorbic acid by visual titration,
but, in view of the fairly high apparent levels of ascorbic found, and the
possible presence of reductones, it was desirable to study representative
canned samples to determine what portion of the apparent ascorbic acid titer
was due to interfering substances. A direct photometric reading (at 540 mp)
of the ascorbic acid osazone in the presence of the osazones of interfering
compounds gave a value of 7 mg of ascorbic acid per 100 g of product instead
of the 11 mg found by the visual titration of the reduced ascorbic acid.
Since it became apparent that there was a large quantity of reductones present
in the sample, it was necessary to chromatographically separate the ascorbic
acid osazone from other interfering osazones in order to properly measure the
total ascorbic acid content. The colorimetric determination of the isolated
ascorbic osazone at 520 my showed that the samples actually contained less
than 0.6 mg ascorbic acid per 100 g. It was concluded that for 1975 and
1976 processing, all significant ascorbic acid activity in the peel pulp was
lost by exposure to high pH, high temperatures, and air (oxygen) contacts
during the peeling process and subsequent processing.
Canned samples of 1975 and 1976 materials were stored to check the color
stability. The 1975 samples were still a bright red after six months at
100°F in tinned lined cans (standard can for tomato products). As a further
check and to eliminate the possible "bleaching" or inhibiting action of the
tin, the 1976 samples were stored in double enameled cans. After nine months
at 100°F, these samples were still "bright"; there was a "slight" darkening
of the serum as happens to tomato products on storage, but this was less than
that of a Grade A commercial puree (21). The color and flavor scores for
the 1976 products are shown in Table 5. Color scores are based on the Hunter
Color-Difference Meter and flavors were determined organoleptically; both
were evaluated by the USDA, Food Safety and Quality Service, Fruit and
Vegetable Quality Division, Processed Products Branch, Stockton, CA.
Consistency, Viscosity, and Pectin—In the recovered peel pulp there
was a desirable, above average number of tomato whole cells which gave the
pulp a heavier, thicker appearance compared to conventional tomato pulps.
In general though, when the consistency or viscosity was measured, this
pulp showed the consistency and viscosity of a good cold-break processed
pulp (Table 6). Serum viscosity approached that of water which indicates
degradation of the pectin as would be expected from the caustic exposure.
Insoluble solids are generally the primary contributors to tomato-product
consistency, but pectin is important because it serves to hold the insoluble
solids in suspension and reduce the tendency for serum separation. The con-
sistency of this recovered peel-pulp would be appropriate for pizza sauce
or soups which normally may use a cold-break pulp because it is desirable
to thicken with starch. For other sauces or pulps where a hot-break
41
-------
material is normally used, combining recovered pulp with conventional pulp
in a ratio of 1:3 results in a material with the consistency and character
of a hot-break pulp.
Samples of peel pulps were evaluated for pectic enzyme activity in both
1975 and 1976, both in the laboratory and from the experimental equipment.
It was concluded that the 1975 recovered peel pulp had little or no pectic
enzyme activity as received when sampled before the heating; therefore, a hot
break is considered unnecessary because there are no enzymes to inactivate.
If, however, the process is modified so that there is substantially less
exposure to caustic, then the hot break could be necessary. Adequate sub-
strate was available in the test since the addition of 0.03% commercial
enzyme (Rohm and Haas No. 59-L, Rohm and Haas Inc., Philadelphia, Penna.) to
the test mixture resulted in a rapid loss of consistency. Without substrate
addition, there was no change in pulp consistency over a period of 1 to 3
TABLE 5. STORAGE STABILITY OF RECOVERED PULP - 1976
Sample
(a)
76007
76009
76011
76013
76021
76023
76025
76027
76031
Comm'l(c)
Color Score (b)
Storage Tem£. & Time
34°F
9 mos .
51.0
51.5
51.9
51.6
50.9
50.8
50.2
49.7
49.3
46.9
1 mo.
51.0
51.3
51.1
51.6
50.8
50.9
50.1
49.3
48.5
46.7
100 °F
3 mos.
50.9
50.9
50.8
51.2
50.5
50.7
49.9
48.9
48.0
46.0
9 mos.
50.4
50.6
50.8
51.2
50.1
49.5
49.3
48.2
47.0
43.1
Flavor (b)
Storage Temp. & Time
34°F
9 mos.
FG
FG
G
G
FG
G
G
G
G
FG
1 mo.
FG
G
G
G
FG
FG
G
G
G
FG
100°F
3 mos.
FG
FG
FG
FG
FG
G
FG
G
G
FG
9 mos.
FG
FG
FG
FG
FG
FG
G
G
G
FG
Total
Solids
salt
free
(%)
6.6
6.8
6.2
7.1
7.2
6.1
5.6
6.1
6.4
14.4
(a) Sample number as embossed on lids of canned samples; 76 ™ year an OXX is
the sample and trial number.
(b) Color Grade A, is 45-50, Grade C is 40-44 for canned tomato pulp. Color
determined using the Hunter Lab Color-Difference Meter D25D-2 with type A
optical head and formula: Score - -122 + 4.139L - 0.081883L2 + 130.572
(a/ Va2 + b2). For flavor, FG =• fairly good. G = good.
(c) Pulp samples judged at total solids shown, except commercial sample was
diluted to 8.5% NTSS.
42
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TABLE 6. CANNED SAMPLES OF RECOVERED PULPS, 1976
Sample
(1976)
(a)
76003
76004
76005
76006
76007
76009
76011
76013
76015
76017
76019
76021
76023
76025
76026
76026 OM
76027
76029
76031
76033
76035
75037
76039
76041
76043
76045
Avg.
CCTJ (g)
CCTP (h)
pH
3.7
4.2
4.0
4.1
4.15
4.25
4.3
4.45
4.15
4.05
4.1
4.1
4.05
4.1
4.3
4.2
4.05
4.1
4.25
4.0
4.15
4.1
4.1
4.1
4.15
4.1
4.13
4.2
4.3
NaCl
(% w/w)
(b)
1.07
1.24
.97
2.22
1.72
.93
.94
.92
.90
1.31
1.38
1.13
1.42
.94
1.04
1.12
1.04
1.46
1.16
0.98
0.99
1.0
0.92
1.08
0.84
0.92
1.14
0.50
0.17
NTSS
(% w/w)
(c)
3.8
4.7
4.6
4.5
5.6
5.6
5.0
5.8
5.2
5.0
6.3
5.7
4.5
4.5
4.2
4.0
5.9
5.7
6.0
4.6
4.8
4.3
4.6
4.6
4.6
4.9
5.0
6.4
12.2
Total
Solids
(% w/w)
(d)
5.4
6.7
6.2
7.3
9.1
7.7
6.8
7.6
7.2
7.5
8.6
7.8
6.6
6.5
5.8
5.9
7.1
7.7
7.7
6.3
6.4
6.0
6.2
6.6
6.4
6.6
6.9
6.7
12.75
Flowtube
Viscosity
(sec)
(e)
50
146
158
206
286
252
213
232
242
406
534
280
218
140
173
261
181
122
180
178
229
196
217
304
302
312
231
70 (i)
~ (j)
Quality
Grade
(f)
A
A
A
A
C
A
A
A
A
A
C
C
A
A
C
C
A
A
A
C
C
C
C
A
C
A
62 U
A to C
A to C
(continued)
43
-------
TABLE 6. (continued)
(a) Sample number as embossed on lids; missing even-numbered cans contained
peeled, whole tomatoes.
(b) NaCl, sodium chloride (salt).
(c) NTSS, natural tomato soluble solids; does not include NaCl from acidifi-
cation.
(d) Total Solids, includes NaCl from acidification.
(e) Flowtube Viscosity, seconds per 5 ml sample.
(f) Quality Grade (except CCTJ), samples graded as tomato puree for color,
defects, and flavor using puree standards (Reference 21), without solids
content qualification, by USDA Fruit and Vegetable Quality Division,
Food Safety and Quality Service, Stockton, California. Ten samples
graded C because of speck defects; samples had good flavor except nine
which were fairly good, and one which had a tin flavor. Trial conditions
varied as process variables were being investigated, primarily as related
to pretreatment and peeling aids.
(g) CCTJ, commercial canned tomato juice; typical averages, salted product,
single strength.
(h) CCTP, commercial canned tomato puree; typical averages, unsalted product,
concentrated.
(i) Juice range was 28-148 seconds.
(j) Puree is much more viscous than juice, measured by a Bostwick consisto-
meter, and Bostwick readings are not convertible to Flowtube Viscosity.
hours. The literature (29) indicates the sensitivity of pectin to caustic
conditions; for example, a solution at room temperature and containing
0.03 g of pectin per 100 ml was completely hydrolyzed in 30 minutes with
0.4% sodium hydroxide, or in about 10 minutes with 0.08% sodium hydroxide.
By contrast, the tomato surface is exposed in cannery operations to 10 to 18%
caustic at 200 to 210°F for 30 seconds, then further exposed to about 1.5%
caustic for 5 minutes at temperatures declining to 110°F. Caustic peeling
depends not only on applying the caustic to the outer surface of the tomato
but also on the caustic permeating the skin; therefore, if pectin is to be
retained in the recovered pulp, consideration must be given to what occurs
in the caustic bath.
Therefore, trials were made on acidifying the tomato surface before
peel removal in lieu of acidifying the peel after removal. Tomatoes were
dipped and cooled in dilute hydrochloric acid immediately after removal from
the caustic bath. The peel was removed manually, the pulp taken from the
skin, and serum viscosity and peroxidase activity were checked. Also, raw
tomato pulp was raised to pH 11, heated, re-acidified, and checked. Results
were similar in both cases though some "virgin" pulp was inevitably included
when hand peeling and the pectin and peroxidase therefore appeared (incor-
rectly) to have been only partially affected by the caustic. In general, the
serum viscosity approached 1 cp and the peroxidase was inactivated when
the tomato or pulp was exposed to pH 11.4 and 180°F for 40 sec; at 80°F and
40 sec exposure serum viscosity was still nil and there was no peroxidase
activity.
44
-------
From these 1975 and 1976 results there is no apparent need to further
consider enzyme inactivation, whether pectinase or peroxldase. However,
since the acidified pulp has a temperature of 100 to 130°F, consideration
should be given in a commercial installation to heating acidified peel with
a hot macerate going to a pulper-finisher; this avoids putting in a heating
operation solely for recovering peel pulp. Such a decision will be affected
by both production and regulatory considerations.
Amino Acids—Since there is only about 1% protein in tomatoes, this
would not normally be considered a significant dietary source of protein.
This is reflected in the general use of tomatoes in sauces and catsup, the
main exception being tomato juice which is considered a source of ascorbic
acid (Vitamin C). However, amlno acids are worthy of analysis because they
can indicate the amount of exposure to alkali and heat. Such a chemical
index of processing effects could be used for future process modifications
to obtain optimum product quality. Certain amino acids are affected more
than others by high pH and heat, and, therefore, their relative changes can
be used as indices of process induced changes.
Amino acid levels in the acid hydrolysates of 1975 and 1976 samples of
recovered peel pulps were determined and compared with those of fresh and
conventionally processed tomato pulp. Exposure of tomato pulp to caustic
during the peeling process resulted in the degradation of certain amino
acids, the degree of which depended on the exposure (time, pH, and tempera-
ture). Arginine, which is known to be unstable to caustic, was significantly
lower in the recovered pulp samples than in either the fresh or the conven-
tionally processed samples. The ratio of arginine to a more stable amino
acid, such as isoleucine or histidine, was chosen as an index of the product
condition. For example, the mean arginine to histidine (A/H) ratio calcu-
lated for conventionally processed tomato (A/H - 1.30) was closer to that
of raw tomato (A/H - 1.30) than was that of recovered pulp (A/H - 0.35 in
1975 and 1.06 in 1976). Thus, the data indicate that the unstable amino
acids in the recovered pulp samples were altered to a greater degree than
those in conventionally processed tomatoes. In conventionally caustic
peeled tomatoes, such changes occur at the tomato surface, which is rinsed,
and do not alter the general amino acid content. Nevertheless, the 1976
recovered peel pulps were altered much less than in 1975. Therefore, the
A/H ratio was found to be a sensitive and objective indicator of pulp proces-
sing history that was also in general agreement with color and flavor grades.
On the basis of the Kjeldahl assays, it appears that about 24 to 27% of
the total nitrogen (protein) content of the tomato samples exists in the
insoluble fraction of both the conventional and the experimental products.
This similarity suggests that there was little or no change in protein solu-
bility resulting from exposure to heat and high pH.
Product Mold, Insect Fragments and Bacterial Counts—In 1975 the peel
taken from the commercial peeling operation was almost devoid of mesophilic
and thermophilic bacteria, and the levels were insignificant compared to
those in normal cannery operations at a comparable point in processing.
Bacterial counts were made to check the cleanliness of the equipment, to
see if there was a significant difference before and after the heating
45
-------
(hot break), and to judge the microbiological stability of the peel coming
from the commercial peeling. As it turned out, the caustic peel is inher-
ently microbiologically stable and normal cleanup and sanitation procedures
would be adequate. Therefore, it can be assumed that the caustic-peeling
operation at high pH and 200-210°F does have a strong bactericidal effect
and that the caustic remaining on the peel has a bacteristatic action.
Also in 1975, the mold and insect-fragment counts on the canned, recov-
ered pulp were uniformly low and reflect the thorough washing and sorting
system at the cannery which was described earlier (see Washing and Sorting).
These microscopic counts were well under the maximum mold count tolerance for
tomato juice (20% of the Howard slide fields) and therefore similar to that
normally encountered in commercial products. In so far as this cannery was
typical of the industry, the existing raw product cleaning procedures would
seem quite adequate if peel pulp is recovered. In 1976 there was experi-
mental freedom to vary sorting. Truck loads with a California State Grading
Certificate showing 1% or less mold required minimal or no sorting to stay
within mold tolerance; if graded as 3% mold, up to 20% of the tomato weight
might need to be removed so as to stay within tolerance. This 207, included
both tomatoes showing mold and broken tomatoes which would subsequently
disintegrate in the caustic bath or not yield properly peeled whole tomatoes.
In general, when the California State load grade certificate shows 3% or
more, particular attention must be given to sorting. The elapsed time
between picking, State grading, and processing, as well as the seasonal
period, will modify the amount of sorting needed.
Bacterial plate counts were made on samples from three consecutive days
in 1975 (October 14, 15, 16) with varying types of "cleanup". Up to October
14, the equipment was flushed with water at the end of the operating day and
the tomato pulp residues in open vessels were removed by hand scrubbing.
For October 15, the equipment was washed as usual, but a 10 ppm chlorine
solution was put into the equipment overnight; the upper surface of hori-
zontal pipes was assumed to be free of tomato material. Preparatory to
October 16, the piping and equipment was disassembled, hand scrubbed, and
rinsed with 100 ppm chlorine solution, drained, and rinsed with potable
water. Pulp samples were taken before and after the hot break, at the pulp
tank, and from the 200-gal holding tanks used for the material balance.
On October 14, the total plate count varied from 6,000 to 17,000 per ml of
tomato peel pulp depending on sample location; this is a much lower count
than might be expected in conventional cannery operations after the hot
break stage, and is attributed to the caustic peeling operation. In the
October 14 samples, vegetative cells were found but no spores. The impli-
cation is that the hot caustic peeling reduced the count, but that there
was some re-inoculation, possibly from unclean experimental equipment or
from the atmosphere since the vessels were open. On October 15 and 16,
the counts were zero for both vegetative cells and spores. Since this
equipment was not operated on a 24-hour basis, this information should
not be extrapolated to a round-the-clock operation.
Pesticides—Various pesticides are applied in the tomato field to
protect crops from the time of planting through harvesting. Although
the use and application of all pesticides are closely regulated by the
46
-------
Enviromental Protection Agency, pesticide residues are unavoidably on the
surface of delivered produce. To assure that the levels of pesticides in
the final products are well below toxic concentrations, maximum permissible
levels have been established by the FDA. Previous studies have shown that
pesticide residues on raw tomatoes are contained almost exclusively in the
waxy layer overlaying the skin. Since the peel residual, from which pulp
was being recovered during this study, contained an extremely high percentage
of skin, samples collected from the test system were analyzed for pesticide
residues (Table 7). Crop histories of the tomatoes delivered to the plant
indicated that toxaphene (a chlorinated camphene containing 67-69% chlorine;
also called camphechlor) was used most widely. Thiodan (a chlorinated
hydrocarbon) and parathion (an organophosphate) were used to a lesser extent.
All of these are detectable by gas chromatography. Appropriate samples were
analyzed for each of the three pesticides. The pesticide counts in 1976 were
similar to 1975, but the 1976 skin waste and recovered pulps were obtained
from a short time (two minutes) batch separation of pulp. Therefore, the
1975 results are considered to be more indicative of a commercial operation.
The legal tolerance (maximum) for toxaphene residue on foods was 7.0 ppm
in 1975 and 1976. Table 7 shows both the average and range of toxaphene in
the recovered pulp for 1975 with an average of 0.4 ppm in the recovered
(100%) pulp, i.e. about 6% of tolerance, and none of the samples were above
tolerance. The 35 ppm average in the skin fraction illustrates the need to
separate the skin from the pulp. The effects of the finisher clearance and
skin size on separation of the skin from the pulp was discussed under the
heading "Pulp Extraction". A close clearance between the finisher paddles
and screen will cause the skin to pass through the screen with the pulp, and
this high skin content can result in a high pesticide content in the pulp.
Regulations prohibit bringing over-tolerance materials into compliance by
dilution. Therefore, prudent manufacturing practice dictates the need for
an adequate fractionation of skin from the pulp.
U.S. Standards of Identity—Since the proposed process modifications
and materials may or may not be totally covered by the existing U.S. Food and
Drug Regulations, the FDA Bureau of Foods was consulted on the following
concerns: (1) utilization of pulp derived from caustic peelings, (2) acidi-
fication of the caustic peel with food-grade hydrochloric acid, (3) use of
food-grade caprylic (octanoic) acid as a peeling aid with residue present
in the recovered pulp, and (4) the labeling requirements when recovered pulp
is utilized. Whether a commercial installation and product would meet the
existing, and currently being revised, regulations, or whether further
technical and regulatory considerations are needed, will depend on FDA judg-
ment. Pertinent regulations in 1975-76 were the former 21 CFR 53.10-0.40,
tomato products; 21 CFR 121.1070, food-grade fatty acids; and 121.1091,
chemicals used in lye peeling. A reorganization and republication of regu-
lations on food for human consumption appeared on March 15, 1977 in 42
FR 14302-14306; this cross references the old and new section numbers. The
United States Standards for Grades of Canned Tomato Puree and Canned Tomatoes
are set forth in 29 FR 9838 (1964) and amended in 35 FR 3651 (1970) and 29
FR 7909 (1964).
47
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TABLE 7. PESTICIDE RESIDUES IN RECOVERED PEEL PULP
Toxaphene
No. of
Sample, 1975 Samples
Whole tomatoes
(fresh)
Peeled tomatoes
(before canning)
*- Caustic peelings before
pulp extraction
Peel skin (after
pulp extraction) (b)
Peel pulp (after
pulp extraction) (b)
3
3
5
20
27
Average
(ppm)
0.2
nd
0.2
35.
0.4
Range No . of
(ppm) Samples
(a)
0.2 - 0.3 3
nd 3
nd - 0.4 5
3. - 150. 7
nd - 4.8 10
Thiodan
Average
(ppm)
0.01
nd
0.00(2)
0.04
0.00(1)
Parathion
Range No . of
(ppm) Samples
(a)
nd-0.02
nd-nd
nd-0.01
nd-0.15
nd-0.01
3
3
5
7
10
Average Range
(ppm) (ppm)
nd
nd
0.01
0.03
nd
(a)
nd— nd
nd-nd
nd-0.06
nd-0.08
nd-nd
nd = none detected
(a) Detection limit =0.1 ppm for Toxaphene; 0.01 ppm for Thiodan and Parathion.
(b) Pulp Extractor normally set with 0.5-inch paddle-screen clearance; screen hole size varied from
0.033 to 0.125-inch. Range also includes other screens and clearances.
-------
Currently, the tomato Standards of Identity are being revised and
re-written by FDA with consideration given to the present CODEX regulations
and present day needs. To the readers of these or past regulations, they
should be aware of the fact that it is not only the wording of regulations
that are of consequence, but the intent (unwritten) as well.
A proposed affirmation of GRAS status for caprylic acid as an indirect
and direct human food ingredient was published on June 14, 1977 (28). This
proposal is subject to public comment, revision, and approval. The signifi-
cance of this GRAS status would place caprylic acid in the status of an
ingredient rather than that of an additive, though possibly just as a flavor.
Use levels are proposed in the new paragraph. The new paragraph 184.1025d
(28) proposes that the ingredient (caprylic acid) be used in foods at levels
not to exceed good manufacturing practices (GMP) and that for food categories
not specifically mentioned, GMP results in maximum levels, as served, of
0.001% (10 ppm) or less. The expected use of recovered peel pulp in tomato
products, as consumed, would be below this 0.001% level. The current regula-
tions (Standards of Identity) do not address utilization of recovered tomato
peel pulp directly, although the liquid from peels and cores may be used as
a packing media for canned tomatoes and for manufacturing canned puree and
catsup (155.190-.194). The Standards of Identity are now being revised and
will influence the future utility of recovered peel pulp.
Effluents and Wastes—One of the prime considerations when initiating
the project was not only to reduce liquid and solid effluents in terms of
caustic, BOD, and COD, but to avoid creating new ones; this was successfully
managed. There was no continuous liquid discharge except from washing the
tomatoes, and this is present commercial practice. In the 1976 Modified
Caustic Peeling system, there was a carryover of peeling aid from the Pre-
treatment to the Caustic Applicator, and from the Applicator to the disc peel
remover. These carryovers were food-grade materials, not inedible peeling
aids nor effluents. Since 96% of the peel is recovered as pulp, the normal
peel effluent was drastically reduced. It was reduced by fractionating the
96% edible material from the 4% non-edible skin and seeds (from tomatoes dis-
integrated during processing). The skin, seeds, and fibers separated by the
Extractor are normal processing wastes. Since these skins and seeds have
been re-acidified, they are more acceptable and in smaller quantity than
the current caustic peel for disposal on agricultural land or into a public
sanitary landfill site. The pretreatment bath liquid was not operated for
extended periods, and though BOD and COD measurements were made, these likely
do not represent what might be experienced under commercial conditions.
Some canners currently operate their caustic applicators the full 3-mo.
processing season without changing solutions; others change the caustic once
a week. The pretreatment solution of octanoic (caprylic) acid and water is
biodegradable, whereas some of the current peeling aids are not. After peel
removal, all canners rinse or flume the peeled tomatoes and this practice
would be unaffected by modified caustic peeling. Therefore, this modified
caustic peeling and peel recovery, while not affecting liquid effluents,
would decrease current peel solids discharge by 96%, and the discharge would
have an improved pH character.
49
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Economics—The economics for a cannery-peeling operation of 40 t/hr are
summarized in Table 8. This assumed installation has the general features of
a projected average situation containing the components of the Modified Caus-
tic Peeling System. An actual installation, in a specific cannery, will vary
according to available space, existing equipment, and production requirements
for tomato products. Such a peeling operation might use two caustic applica-
tors, such as the FMC Hi-Ton, and either two FMC PR-20 Peel Removers, four
Magnuson Model C Peel Scrubbers, or equivalent dry mechanical peel removers
that do not add water to the peel. The costs and values shown are presented
as an example and should be adjusted with local data. These costs are based
on 1976 information, a 12% recoverable peel, 60 days of operation per year,
16 hours of peeling each day, and a $50/t pulp value. While the trend of
costs is upward and is expected to continue up, the relative spread between
costs and value is expected to remain about the same for the coming few years.
Capital and operating expenses include only those directly associated
with pretreatment and pulp recovery, not the balance of the peeling process
that is presumed to already exist. The capital cost could easily be smaller
or greater, depending on whether existing equipment and utilities are readily
adaptable or entirely new equipment would be needed. One example is that the
pretreatment could be applied with an existing flume that is converted to
heated, recirculated liquid, or it might require a special tank with con-
trolled immersion time for the tomatoes, such as that used in the pilot
installation during 1976.
There is a significant cost reduction in peel waste disposal because
96% of the peel can be recovered as pulp and only 4% remains as true waste
for disposal. A cost of $2.50/t was used for the current disposal of caustic
peel, and this is a minimum as the range is $2.50 to $5.00/t. For the
installed Capital Equipment, a significant potential difference exists
between this estimate and an actual installation. The amount of electrical
and piping supply installation is subject to existing facilities; for
instance, if a flume is used for the pretreatment with peeling aid, a 50 hp
electric motor might be required for a recirculation pump, and such a load
could require adding major electrical power capacity in that area. The
balance of the fixed and variable costs are fairly predictable, but for
each year after 1976, about 10% per year should be added as an inflation
factor.
The capital costs associated with peel pulp recovery can potentially
be recovered within one year as indicated in Table 8. Therefore, the
recovery of peel pulp appears to be self supporting, hence economically
viable and attractive. Since other plant operations are not affected by
pulp recovery, the economic risk is considered to be limited to the recovery
process.
50
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TABLE 8. PROJECTED ECONOMICS OF A COMMERCIAL INSTALLATION
Based on: 40 t/hr tomatoes x 12% peel
= 4.8 t/hr peel 96% recovery
= 4.608 t/hr pulp recovered.
60 dy/yr x 16 hr/dy = 960 hr/yr
Recovered Peel-Pul£ Value
Based on $50/t gross value of pulp.
Fixed Cost, installed Capital Equipment
Depreciated in 1 yr, 960 hr.
Pretreatment (circulation, temp, control) -
Chemical Supplies (tanks, pumps, piping)
Extraction (pulper, piping)
Acidification (pH control, agitator)
General (utilities, piping, etc.) -
Contingency
(installed total) -1
Variable Costs
Direct Labor (operator, cleanup, QC, supv.) -
Startup labor, 1st year
Indirect labor (mechanic, clerk)
Superintendence
Utilities, steam, 7,230 Ib/hr
water, 10 gpm
electricity, 78 kw
Chemicals, fatty acid, 1.33 Ib/hr
hydrochloric acid, 150 Ib/hr -
Maintenance Supplies, 5%/yr of capital
Miscellaneous (operating & cleanup supplies)-
Value
Costs
NET RETURN ON PEEL PROCESSING
Saving on Caustic Peel Disposal ($2.50/t)
OVERALL RETURN ON PEEL PROCESSING
15,000
16,000
14,000
15,000
35,000
20,000
15,000
12.48
24.96
3.13
0.94
10.84
0.07
1.57
1.33
6.00
5.99
1.00
1st Year
Operation
($/hr)
+ 230.40
- 119.79
- 40.57
0.94
12.48
7.33
5.99
1.00
+ $230.40
- 188.10
+ $ 42.30
-1- 12.00
+ $ 54.30
or
$52,128.00
1st year
2nd Year
and
Thereafter
($/hr)
+ 230.40
0.00
15.61
0.94
12.48
7.33
5.99
1.00
+ $230.40
- 43.35
+ $187.05
+ 12.00
+ $199.05
or
$191,088.20
thereafter
51
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REFERENCES
1. Schultz, W. G., R. P. Graham, and M. R. Hart. Pulp recovery from tomato
peel residue. Proceedings of 6th National Symposium on Food Processsing
Wastes, Madison, Wisconsin, April 5-11, 1975.
2. Hart, M. R., R. P. Graham, G. W. Williams, and P. F. Hanni. Lye peeling
of tomatoes using rotating rubber discs. Food Technology 28:38, 1974.
3. Ostertag, R., and K. Robe. Waterless peel removal. Food Processing
36:60, Jan. 1975.
4. Schultz, W. G., R. P. Graham, W. C. Rockwell, J. L. Bomben, J. C. Miers,
and J. R. Wagner. Field processing of tomatoes, Part 1, process and
design. J. Food Sci. 36:397, 1971.
5. Miers, J. C., J. R. Wagner, Nutting, M-D., W. G. Schultz, R. Becker,
H. J. Neumann, W. C. Dietrich, and D. W. Sanshuck. Field processing of
tomatoes, Part 2, quality and composition. J. Food Sci. 36:400, 1971.
6. 38 FR 27076. Asbestos Particles in Food and Drugs, Sept. 28, 1973.
7. 40 FR 26683-4. Electroyltic Diaphragm Process for Salt, 1975.
8. Dahl, S. A. Chlor-alkali cell features new ion-exchange membrane.
Chem. Engr. 82:17, 1975.
9. 21 CFR 113. Thermally Processed Low-acid Foods Packaged in Hermetically
sealed containers, 1977.
10. Horowitz, William (ed.). Official Methods of Analysis of the Associa-
tion of Official Analytical Chemists. AOAC, Washington, D.C., llth ed.,
1970. p 560.
11. ibid, p 560.
12. National Canners Assn. Laboratory Manual for Food Canners and Proces-
sors, Vol. 2. The AVI Publishing Co., Inc., Westport, Conn., 1968.
pp 291 - 292.
13. ibid, p 341.
14. ibid, pp 294 - 296.
52
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15. Horowitz, W. loc. cit. p 369.
16. ibid, pp 769 - 771.
17. Assoc. Vitamin Chem. "Methods of Vitamin Assay", 3rd Ed., 1966.
pp. 320-327,
18. ibid, pp 332 - 338.
19. Food and Drug Administration. Pesticide Analytical Manual, Vol. 1.
U.S. Dept. of HEW, Washington, D.C., 1971 §212.13a(2).
20. National Canners Assn. loc. cit. pp 300 - 316, 324 - 325.
21. 35 FR 3651. Canned Tomato Puree (Tomato Pulp), 1970.
22. Assoc. Offie. Agr. Chem. "Official Methods of Analysis, 448, 1960.
23. Spackman, D. H., W. H. Stein, and S. Moore. Automatic recording
apparatus for use in the chromatography of amino acids. Anal. Chem.
30:1190, 1958.
24. Wagner, J. R., and J. C. Miers. Consistency of tomato products. Food
Technology 21:920, 1967.
25. Horowitz, W. loc. cit. pp 777-778.
26. 21 CFR. 173.315. Chemicals Used in Washing or to Assist in the Lye
Peeling of Fruits and Vegetables, 1977.
27. 21 CFR 172.860. Fatty Acids, 1977.
28. 42 FR 30390-1. Caprylic Acid, 1977.
29. Joslyn, M. A. "Methods of Food Analysis", Academic Press, 1950.
pp 455-56.
30. USDHEW, Public Health Service, Food and Drug Adra., HFF-342, Washington,
D.C. 20204. "The Food Defect Action Levels", 11-12, August 1977.
31. Method of Peeling Fruits and Vegetables with Carboxylic Acids, SN 714,
229. National Technical Information Service, U.S. Department of
Commerce, 425 Thirteenth St., NW, Washington, D. C. 20204.
32. Amoore, J. E., D. Venstrom, and A. R. Davis. Measurement of Specific
Anosmia. Perceptual and Motor Skills. 26: 143-164, 1968.
33. Kohler, G. 0., and Palter R. Studies on methods for amino acid analysis
of wheat products. Cereal Chem. 44:512, 1967.
34. Martin, J. T., and B. E. Juniper. "The Cuticles of Plants". Arnold
Publ., 1970.
53
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35. Beaman, D. R., F. P. Boer, C. T. Lichy, R. J. Moolenaar, F. W. Spillers,
0. C. Taylor, and D. M. Young. Abestos in Water in the Chlor-Alkali
Industry. The Chlorine Institute, 17th Chlorine Plant Managers'
Seminar, New Orleans, Louisiana, February 5, 1975.
54
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BIBLIOGRAPHY
29 FR 7909 Grades of Canned Tomatoes, July 24, 1969.
21 CFR 155.190(a) -.190(b), -.190(c) -.191, -.192, and -.194. Standards
of Identity - Canned Tomatoes, Tomato Paste, Tomato Puree, Catsup, 1977,
U.S.D.A. "Composition of Foods", Agriculture Handbook No. 8. U.S. Govern-
ment Printing Office, Washington, D. C., 1963.
Wilson, L., and Sterling, C. Studies on the Cuticle of Tomato Fruit.
Zeitschrift fur Planzenphysiologie, Vol. 77, pp. 359-371, 1976.
42 FR 10004-10009. Canned Tomatoes, proposed United States Standards for
Grades, 1977.
42 FR 1000-100013. Canned Stewed Tomatoes, proposed United States Standards
for Grades, 1977.
55
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APPENDIX A
Vitamin A Activity Method*
Reagents
Acetone: Dry, alcohol-free reagent grade.
Petroleum Ether: redistill in all-glass apparatus collect 60-70° fraction
Adsorbent: mix for 1-2 hours 1+1 activated magnesia (MgO from Merck Co.,
Rahway, New Jersey) and Hyflo Super-Gel (diatomaceous earth
from Fischer Scientific Company, Fair Lawn, New Jersey).
Extraction
Work in subdued light.
Weigh 10-50 grams sample into blender cup. Sample size depends on
amount of International Units per 100 grams sample: less than 100 to 200
I.U./100 g. needs 50 grams sample, 200 to 1000 I.U./100 g. needs 25 grams
sample, and more than 1000 ILU./100 g. needs 5-10 grams sample.
Add 200 ml 50:50 petroleum ether:ethanol. Add approximately 2 grains
filter aid. Blend at high speed for 5 minutes. Filter through fast flow
Whatman filter paper on Buchner funnel into 500 ml Erlenmeyer flask connected
to vacuum. Rinse blender cup with water and then with petroleum ether into
funnel.
Transfer filtrate to 500 ml separatory funnel rinsing first with petro-
leum ether then with water.
Scrape residue from filter paper back into blender cup. Add 100 ml
50:50 petroleum ether:ethanol. Blend at medium speed for three minutes.
Filter contents from second blending through same filter paper into
same 500 ml Erlenmeyer flask. If filtrate is colored re-extract in the
same manner until clear, each time transferring filtrate quantitatively to
separatory funnel.
Drain water layer in separatory funnel to an Erlenmeyer flask. Swirl
vigorously with 50 ml petroleum ether. Add back to separatory funnel.
Drain and discard water layer. Wash filtrate with 100 ml portions of water
until water layer is clear, about five times. Swirl with a rotary motion.
Drain off as much water as possible. Filter through 10 grams anhydrous
sodium sulfate into appropriate size beaker. Rinse separatory funnel and
*For regular tomato materials @pH 4.0 to 4.5.
56
-------
sodium sulfate with 50 ml petroleum ether into beaker. Evaporate extract
to 50-25 ml under warm air in hot water bath.
Column
Chromatographic tube should be 175 mm long with an outer diameter of
22 mm and a constriction at the bottom of 10 mm. A reservoir for holding
eluant (solvent) at the top is convenient.
Plug base of tube with glass wool. Add loose adsorbent to 15 cm depth.
Apply vacuum and tamp with tight fitting rod to 7 cm depth making sure sur-
face is flat. Add 0.5 cc anhydrous sodium sulfate.
Elution
Pre-wet column with petroleum ether. Adjust flow rate to 2-3 drops
per second by air pressure from above. Do not let column go dry. Transfer
entire extract to column. Load by rinsing beaker and reservoir with small
portions of petroleum ether just as extract has reached about 1 cm above
column.
Elute first carotene band with 5% acetone in petroleum ether. Collect
in graduated cylinder. Elute second xanthophyll band with 10% acetone in
petroleum ether and collect in graduated cylinder.
Calibration of Spectrophotometer
Standard Stock Solution: 1.0 mM
dry crystalline l-(Phenylazo)-
2-napthol (C.I. Solvent Yellow;
Sudan 1) to constant weight in 70°F
vacuum oven. Dissolve 0.1241 g in
500 ml acetone-isopropanol (1 +1).
Store in dark.
Working Solution: 0.04 mM
Dilute 20 ml stock solution to 500 ml with acetone-
isopropanol (1 +1). Store in dark.
Working solution should read 0.460 at 436 my and 0.561 at 474 my with
slit width of 0.03. The instrument deviation factor, f, is the ratio of the
theoretical absorbance to the actual. Assume that the working solution of
dye has the same A as 2.35 mg carotenes per liter at 436 my and 2.38 mg
xanthophylls per liter at 474 my.
Read first band at 436 my and second band at 474 my.
57
-------
Calculation
Carotenes
I.U./100 g = A436 x f x final volume x 1667 x 100
196 x g on column x b
where f = instrument deviation factor, 1667 = international units vitamin A
activity per gram, and 196 = the extinction coefficient (A = .460/2.35 rag
carotenes per liter), and b = cell length in cm.
Xanthophylls
I.U./100 g - A474 x f x final volume x 1667 x 100
236 x g on column x b x 2
The activity is divided by two since this group of carotenoids have about 50%
biological activity.
Reference: AOAC 39,014 - 39,023, Eleventh Edition, 1970.
58
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APPENDIX B
Photometric Determination of Anionic Peeling Aids*
[Sodium 2-ethylhexyl sulfate and sodium mono-
and di-methyl naphthalene sulfonate]
Solutions and Chemicals
1. Chloroform (Spectrophotometric and Technical grade).
2. Methylene Blue Indicator.
0.03 grams Methylene Blue (N. F. Powder).
12.00 grams Concentrated Sulfuric Acid (ACS).
20.00 grams Sodium Sulfate (anhydrous) ACS.
Dissolve the above ingredients to 1 liter with deionized water
(detergent free). Extract in a 1 liter separatory funnel by shaking
with Technical grade Chloroform until the Chloroform layer does not
show any variation when compared to an aliquot of Technical grade at
600 wavelength.
3. Deionized water (detergent free).
4. Sulfuric Acid 5N.
Dilute 140 ml of Cone. Sulfuric Acid (ACS) to a liter with deionized
water (detergent free).
Apparatus
1. Volumetric flasks-100 ml.
2. Volumetric pipettes - 1, 2, 4, 5, 10, 20 ml. sizes.
3. Separatory funnel, 250 ml & 1 liter.
4. 30 ml screw cap test tubes.
5. Photometer capable of measuring at 600 my.
Procedure
Pipette 5 ml. of caustic peel sample into a 100 ml volumetric flask and
fill with deionized water (detergent free) to the mark, shake and pipette
5 ml of this diluted solution into a 250 ml separatory funnel. Add 5 ml of
5 N sulfuric Acid and 20 ml of Technical grade chloroform, stopper funnel,
and shake for one-half minute. Permit time for the chloroform layer to
separate and discard. Add another 20 ml of chloroform, stopper funnel,
and shake for one-half minute. Permit time for the chloroform layer to
*Modification of a methods published by Intercontinental Chemical Co.,
P.O. Box 15318, Sacramento, CA 95813 and Union Carbide Inc., 270 Park Ave.,
New York, NY 10017.
59
-------
separate and discard. Add 20 ml of Methylene Blue solution and 20 ml of
Spectophotometric grade chloroform to a separatory funnel, shake for one
full minute and allow layers to separate as before. Very carefully draw
off the chloroform layer into a 30 ml screw cap test tube. Transfer chloro-
form to Photometric Cuvette and measure the optical density at 600 mp.
To establish a standardization curve, make solutions containing exactly
0, 5, 10, 20, 30, 40, 50 ppm of peeling aid and analyze according to the out-
lined procedure, omitting the Technical grade chloroform steps. In a graph,
plot ppm of concentration of peeling aid against the optical density as the
examples in Figure B-l.
60
-------
CO
0.7
0.6
0.5
0.4
ii 0.3
D.
o
0.2
0.1
SODIUM 2-ETHYLHEXYL SULFATE
AT 600 nip WAVE LENGTH
(TYPICAL STANDARDIZATION CURVE)
— TOMATO SAMPLE, 10% TS
AQUEOUS STD
SODIUM MONO- AND DI-METHYL
NAPHTHALENE SULFONATES
AT 645 mi*. WAVE LENGTH
TOMATO SAMPLE, 10% TS
AQUEOUS STD
1
1
I
1
1
1
10 15 20 25 30 35 40
PEELING AID, AS 100% ACTIVE INGREDIENT (PPM)
45
50
-------
APPENDIX C
Determination of Fatty Acids in Processed Tomato Products.
Analytical Procedure
Principle
This method involves the extraction of fatty acids (and their salts)
from processed tomato products and the formation of their propyl esters for
their quantitative determination by gas liquid chromatography. This method
is applicable to the analysis of C/- to C,Q fatty acids in tomatoes that
have been treated with such materials during their processing (peeling).
This procedure defines the chromatographic retention time and response
of the propyl esters of hexanoic (caproic) acid, heptanoic (enanthic) acid,
octanoic (caprylic) acid, nonanoic (pelargonic) acid, and decanoic (capric)
acid. The residue of any one or more of these fatty acids is calculated on
the basis of the area of the peak(s) in the sample extract representing the
fatty acid in question. This procedure requires prior knowledge of the
fatty acid(s) present in the sample, since the area of the propyl ester(s) of
the residue is compared to the area of the propyl ester of a similar fatty
acid that is added to the sample as an internal standard.
Apparatus
1. Extraction equipment:
a. 60 ml and 250 ml separatory funnels.
b. 25 and 50 ml graduates.
c. 50 ml boiling flask, 24/40 taper joint.
d. 300 mm West condenser with 24/40 taper joints.
e. steam bath.
f. 250 ml centrifuge bottles.
g. centrifuge.
h. 10 ml volumetric flasks or other vessels with glass stoppers.
i. 10 ml beakers.
j. Pasteur transfer pipets and bulb.
k. Pipets: 1 ml, 2 ml, 5 ml.
2. Gas chromatographic instrument with the following minimal charac-
teristics:
a. Column oven operated with temperature programmed between 80°C
and 170°C, at a rate of 2° to 5° rise per minute.
b. Sample injection port with heater characteristic necessary
for operating about 85°C higher than the maximum necessary
column oven temperature (255°C).
62
-------
c. Detector of the flame ionization type. If separately thermo-
stated, it should be maintained at 255-265°C.
d. Column, 8-1 Oft long, 1/8 inch outside diameter, made of stain-
less steel or glass, packed with 10% by weight FFAP liquid
phase on 60-80 mesh acid washed DMCS Chromosorb W.
e. Recorder, 1 to 100 mv range, 1-sec. full scale deflection with
a chart speed of 1 mm per minute and an attenuator switch to
change the recorder range required. The recorder should be
equipped with an integrator if possible.
f. Helium, nitrogen, or argon; minimum purity 99.95 mol %.
g. Hydrogen, minimum purity 99.95 mol %.
h. Air, dry, dew point -75°F max.
3. Syringe (1 microliter) for sample injection.
Reagents
1. Reagent Purity. Reagent grade chemicals shall be used in all
tests. Unless otherwise indicated, it is intended that all rea-
gents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society, where such
specifications are available. Other grades may be used provided
it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the
determination.
2. Chloroform.
3. Boron Trifluroide - propanol (14% w/v). Store in refrigerator.
(Applied Science Labs, Inc., *State College, PA 16801).
4. 6N - Hydrochloric Acid.
5. Saturated solution of ammonium sulfate.
6. Anhydrous sodium sulfate.
7. Internal Standard. Use heptanoic acid when analyzing for hexanoic
or octanoic acid. Use decanoic acid when analyzing for nonanoic
acid or a mixture of Cg to Cg fatty acids that include heptanoic
acid. Standard solution should be prepared in chloroform.
8. Standard Mixture of Fatty Acids. Quantitatively prepare a mixture
of the fatty acids to be analyzed in approximately equal amounts,
including the fatty acid chosen as the internal standard, e.g.,
about 2 mg of each fatty acid in a total of 2 ml chloroform.
Procedure
1. Extraction
a. For samples of tomato pulp with expected fatty acid residuals
63
-------
of up to about 150 ppm, weight accurately about 40 grams of pulp
into a 250 ml separatory funnel. For larger residuals use a
proportionately smaller sample size.
b. Acidify with 1 ml 6N HC1.
c. Add about 130 ml chloroform and an accurately measured amount of
internal standard (ca 3 mg, preferably as an aliquot from a
standard solution prepared with chloroform).
d. Mix thoroughly for about 2 minutes. If necessary, transfer
to a 25 ml centrifuge bottle and centrifuge sufficiently to
break any emulsion that forms; then transfer to the original
separatory funnel.
e. Remove the chloroform extract (lower phase) to another 250 ml
separatory funnel.
f. Add 20 ml 0.5N NaHC03 and mix thoroughly to extract fatty
acids from chloroform.
g. Allow phases to separate and discard chloroform (lower phase); if
necessary, centrifuge.
h. Acidify with 2 ml 6N HC1. Mix thoroughly until effervescence
stops.
i. If necessary to improve purity of the extract, repeat steps
(c) to (h), using 5 ml in chloroform in step (c) and 5 ml
0.5N NaHC03 in step (f) and 0.5 ml 6N HC1 in step (h) in a
small separatory funnel. Do not add more standard when
repeating extraction.
j. Transfer acidified aqueous phase to 60 ml separatory funnel
and extract fatty acids with 2 ml chloroform.
k. Transfer chloroform extract (lower phase) to a 10 ml beaker
containing 0.4 g anhydrous Na2SO^.
2. Ester formation
a. Decant the clear chloroform extract into a 50 ml boiling
flask.
b. Add 2 ml of boron trifluoride (14% w/v) propanol reagent.
c. Reflux on steam bath for 15 minutes.
d. Cool to room temperature; add 5 ml saturated ammonium sulfate
solution and mix throughly. Transfer to 60 inl separatory
funnel and allow phases to separate.
e. Discard lower (aqueous) phase, and with a Pasteur pipet trans-
fer organic phase to a 10 ml glass-stoppered flask containing
about 0.4 g anhydrous Na2SO^.
f. Refrigerate until chromatographic analysis.
3. Calibration
a. Prepare the propyl esters of the standard mixture of the
fatty acids by using 2 ml of a chloroform solution of the
fatty acids (ca. 2 mg each) in step (a) of ester formation.
Complete steps b-f of ester formation as for sample extracts.
b. Chromatograph the ester solution and adjust the chromatogra-
phic conditions such that there are suitable retention times
and good resolution of the fatty-acid propyl esters.
64
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c. Techniques pertaining to column conditioning, selection of
carrier gas flow rates, peak resolution, sensitivity settings,
sample injection, and attenuation control, etc., should be
patterned after ASTM Method D 1983-69, AOCS Method Ce 1-62
or any other method suitable for the determination of fatty
acid esters, including those suggested by the instrument manu-
facturer.
d. Determine the detector response for each fatty-acid propyl
ester relative to that of the chosen internal standard. The
detector response for esters of fatty acids of similar mole-
cular weight should be very similar. For all practical
purposes, the relative detector response for adjacent peaks
(e.g., Cj and Cg fatty acid propyl esters) may be assumed to
be identical. Therefore, it is preferable to use heptanoic
acid as an internal standard for assaying octanoic acid.
4. Chromatographic analysis
a. Once the optimum chromatographic conditions have been esta-
blished (see calibration), chromatograph the propyl esters
of the sample extract, which includes an internal standard
of fatty acid (e.g., heptanoic acid).
b. Identify the fatty acid propyl ester(s) peak(s) and the
internal standard peak in the chromatograph of the sample
extract.
c. Integrate only these peaks, correcting for the detector
response characteristics of each propyl ester.
d. If no integrator is used, measure the height and width at
half height of each peak in order to estimate its area.
e. Calculate the residue of each fatty acid as follows:
fatty acid residue, ppm * R S x 10 ,
a w
where R » ratio of the subject peak area to the internal
standard peak area
S = weight of internal standard in grams
W = weight of tomato sample in grams
5. Interference
Analysis of tomatoes not treated with fatty acids may show
small amounts of various naturally occurring compounds with reten-
tion times similar to those of the C6 to CIQ fatty acid propyl
esters. Individually, these usually amount to less than 1 ppm
(fatty-acid equivalent), and very often they can be differentiated
from the peaks of the esters being analyzed. If the fatty acid
used in processing the tomatoes has an impurity similar to the
fatty acid used as the internal standard, the results (compared
against the standard) will be slightly low.
65
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-202
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
COMMERCIAL FEASIBILITY OF RECOVERING TOMATO
PROCESSING RESIDUALS FOR FOOD USE
5. REPORT DATE
September 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
W. G. Schultz, II. J. Neumann, J. E. Schade, J. P. Morgan
P. F. Hanni, A. M. Katsuyama & H. Maagdenberg
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
USDA, Western Regional Research Center
Albany, CA, and
National Food Processors Association, Western Research
Laboratory, Berkeley, CA
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
EPA-IAG-D5-0795
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab. - Cinn, OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
FINAL REPORT 5/75-3/77
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A 2-year project was undertaken to determine the commercial feasibility of recovering
pulp from the peelings of caustic peeled tomatoes. In 1975, peel from regular
cannery operations was processed through a 20-gpm (5 t/hr) continuous-flow line.
This processing consisted of acidifying the peel to pH 4.2 with food-grade hydro-
chloric acid, then separating the pulp from the skin with a paddle finisher (screen).
Recovered peel pulp was found to be of food quality but contained high peeling-aid
residues (150-450 ppm). Peeling aids in current use are approved for peeling but not
as additives to the final product. In 1976, a 1-t/hr pilot peeling line was set up at
a cannery to study modifications in the peeling process for the purpose of reducing
peeling-aid residue in the recovered pulp. The principal modification was to pretreat
the tomatoes by immersion in a 150°F aqueous bath (approximately pH 3.6) containing
about 0.15% food-grade octanoic (caprylic) acid; subsequently, the tomatoes were
immersed in caustic. The peel was removed with rubber-disc peelers. Recovered pulp
met USDA Quality Grade A, and the octanoic acid levels were low (0 to 30 ppm). The
proposed use of this recovered peel pulp is in combination with tomato pulp from
regular sources for canned products such as tomato sauce, catsup, paste, and fill
juice for peeled tomatoes. Economic analysis indicates an attractive ROI.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. cos AT I Field/Group
Food Processing
Canning
Byproducts
Economic Analysis
Tomato Peel
Pulp Recovery
68D
is. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
78
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDI TION i s OBSOLETE
66
ftii.s.coniiMicmnwnKornctitTt- 657-060/1491
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