’fl Will." 'Jllfl’llwl I”! it ' 5 WI HEAT EMEUCED SQ: ETEZV’EEG ZN FRESH CUCQAEEL'B 7’ ECKE. E Thus E0? {Em Degree of M. EEECEEEGAE‘E STATE UNEEERSEE; Frederick Eé/Eartin Jeffe 1959 rHEBlI Linn! _ UM ' HEAT-INDUCED SOFTENING IN FRESH CUCUMBER PICKLES By Frederick Martin Joffe AN ABSTRACT Submitted to the College of Agriculture Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Food Technology Program Agricultural Engineering Department 1959 Appmve‘i M%/fl%’ ABSTRACT The texture of fresh cucumber pickles is a matter of con- cern to the producer. Throughout the literature concerned with quality factors in pickle production, there are allusions to the dangers of overheating the product: however, the reported work on heat-induced softening has been limited primarily to studies in support of overall process recommendations. In this study, heat-induced softening of fresh cucum-‘ ber pickles was investigated using a recording pressure tester designed to measure the force required to penetrate the pickle as a function of plunger displacement. A standard testing procedure was developed from a study of apparatus character- istics such as plunger velocity and plunger shape. Fresh cu- cumbers, heat processed at several time-temperature conditions, all more severe than pasteurization requirements, were tested. The resistance to penetration of succesive layers of tissue was determined by testing the loss in pressure when sections of pickle tissue were removed. Results of the heat softening examinations suggest that there is a semilogarithmic relationship between pressure at 3-weeks' storage time and the equivalent minutes at each processing temperature. The logarithm of equivalent minutes required to reduce the pressure to 10 pounds was plotted against processing temperature, and the straight line curve indicated that an increase in temperature of 30° F. caused a decrease in equivalent minutes by a factor of ten. Analysis of the tissue removal tests showed that the resistance of succesive layers of pickle tissue was not the same for fresh and heat processed cucumbers. Fresh cucum- bers had a zone of maximum resistance to penetration in a 2 mm. layer just under the skin, whereas cucumbers heat pro- cessed at 1800 F. for 30 minutes had a zone of maximum re- sistance in the skin. HEAT-INDUCED SOFTENING IN FRESH CUCUMBER PICKLES By Frederick Martin Joffe A THESIS Submitted to the College of Agriculture lMichigan State University of Agriunlture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Food Technology Program Agricultural Engineering Department 1959 ACKNOWLEDGEMENTS The author wishes to express his appreciation to sev- eral peOple for their noteworthy contributions to this paper. Those directly responsible for the production of this work through their efforts are as follows: Dr. R. C. Nicholas, Agricultural Engineering Department, as major professor, contributed innumerable hours of tech- nical assistance, aid in eXperimentation, and patient devo- tion in the production of the manuscript. Dr. I. J. Pflug, Agricultural Engineering Department, provided assistance in the formulation of the experimental procedure, the design of apparatus, and the writing of this thesis. Dr. C. L. Bedford, Department of Horticulture, and Dr. W. D. Powrie, Agricultural Engineering Department, for' their helpful suggestions throughout this work. Dr. A. w. Farrall, Agricultural Engineering Department, for his interest and allocation of funds. Mr. T. J. Mulvaney, Agricultural Engineering Department, for his helpful suggestions throughout the inception, eXperi- mentation, and production of this work. To my wife, Ruth, for her inspiration, devotion, and aid in the reproduction of the manuscript. TABLE OF CONTENTS Page INTRODUCTIONOOOOOOOOOO00.0000000000000000000000000.00.0 1 REVIEE'EIT OF LITERATUREOOO0.00.9.0.0000COOOOOOOOOOOOOOOOOO 3 \N Rheological Considerations........................ Histological Considerations....................... 5 Softening of Pickles.............................. 10 EXPERIMENTAL........................................... 12 Treatment Prior to Heat Processing................ 13 Heat Processing................................... 14 Design and Operation of the Recording Pressure Tester....................... 1: Apparatus Performance Tests....................... 18 Preliminary Storage Tests......................... 22 Heat Softening Tests.............................. 22 Methods Comparison Tests.......................... 23 Tissue Removal Tests.............................. 24 Histological Tests................................ 25 RESULTS................................................ 27 Group I - Machine Operation....................... 27 Group II - Tests on the Raw Product............... 33 Group III - Heat Softening........................ 36 DISCUSSION APED RECOIVJJEENDATIONS. O O 0'. O O O O O O O O O O O O O O O O O O O 0 1+7 Page APPENDIX.CO...0.00.0000.0.0.0.0000...OOOOOOOOOOOOOOOOO. 53 REFERENCES...OlOOOOCOOOOCOOOOOCOOOOOOOOOOOOOOCOOOOOOOOO 56 INTRODUCTION Processors of fresh cucumber pickles are reluctant to overheat their products during pasteurization. The fear of heat-induced softening is widespread and the blame for soft pickles is frequently laid to overheating. This attitude is understandable because ever since the fresh cucumber pic- kle has been produced in appreciable quantities, the pro- ducer has been cautioned against overheating, not only be- cause of threatened softening, but also because of a flavor change. For example, Etchells and Jones (11) have cau- tioned, "...the final product must...be free from undesir- able texture and flavor changes which may result from im- prOper pasteurization, such as overheating." Esselen and Anderson (59), in an article on pasteurization of genuine dill pickles, include as a basic requirement of pasteuri- zation, "...prevention of overpasteurization, which may re- sult in a softening of the pickles...". If heat-induced softening could be measured objectively and a relationship between heat and softening determined, then any deleterious effects on texture brought about by heating could be dis- cussed in an analytical manner. The oEjective in this study has been to develOp a sim- ple texture measuring device, free of human errors, and to determine whether some relationship can be established be- tween texture measurements with this machine and various heat treatments, all more severe than that required to pas- teurize fresh cucumber pickles. The approach to the prob— lem was both physical and rheological. Histological tech- niques were employed to examine gross anatomical changes in- duced in heat processing of pickles; however, these tech- niques were used only as a guide to indicate further experi- mentation in this area. REVIEW OF LITERATURE ~ Rheological Considerations Biting, chewing, or feeling a pickle involves a com- plex set of sensory perceptions. What has been described as firmness or softness of a food product is in reality the integration of a number of psychological and rheological phenomena. The gap between the sensory evaluation and phys- ical phenomena has been investigated by a few workers, notably Scott Blair, COppen, and Harper. Scott Blair and COppen (23) have attempted to describe the physical phe- nomenon of firmness in rheological terms. They state that firmness is a "gestalt", defined by Kohler (Gestalt Psy- chology, 1929) as "...a concrete individual and character- istic entity, existing as something detached and having a shape or form as one of its attributes." Scott Blair fur- ther states that "...a single term 'firmness' is univer- sally used to describe an exceedingly complex set of sen- sory data...". To avoid the fallacy in trying to describe such prOp- erties using physical measurements without the psycholog- ical counterpart involved in sensory perception, Scott Blair and COppen (23) resorted to model systems. Subjec- tive evaluations of firmness were compared to the compres- sion modulus of rubber cylinders. The rubber cylinders (2.5 cm. in length, 2.0 cm. in diameter) were compressed so that the changing cross section was compensated for by in- creasing the load to maintain pressure (force per unit area) constant. Subjective tests were performed by squeezing rub- ber cylinders of various compressibilities. The authors emphasized that: 1. Any force causing a deformation must be divided into its elastic and plastic components. 2. The parameters involved in such measurements vary with the stress-strain condition of the' material. 3. These moduli are only an approximation of the subjective sensory perceptions. In defining firmness, Scott Blair and COppen propose that it is the "...inverse of the extent to which a material changes its form under the influence of unit stress acting for unit time, independent of the extent to which the amount of deformation depends on time". Mathematically, they have expressed firmness according to a general deforma- tion formula of Nutting (18): Y = Ss'1 tk or log I = log S - log s + k log t, where S is shearing stress, 8 is shearing strain, t is time, log Y is firmness, and k is a measure of elasticity, defined as the coefficient of dissipation. Nutting has prOposed that for log Y varying with stress: log YB = B log S - log s + k log t, where B is a measure of the change in elasticity. The value of k is between 0 (completely elastic) and 1 (completely inelas- tic). If the psycho-physical phenomenon of firmness is a gestalt, it is not directly relateable to the gestalt sen- sation of biting a pickle. Although the general descrip- tion of this sensation has been described in the literature variously, as softness or firmness, a better term to define this gestalt might be criSpness. A fresh cucumber, carrot, or even a piece of lettuce has a snap to it when broken. The loss of this snap may be pictured as a loss of criSp- ness. To describe this loss in crispness would require ex- tensive work on the histological and rheological changes involved: therefore, some mention must be made of the histological conditions of the tissue. Histological Considerations Softenipg 9: tissue ig processing The four types of mature tissue in plants, as descri- bed by Weier and Stocking (26) are storage (parenchyma), conducting, supporting, and protecting. In normal paren- chyma, the cell walls are held together by pectinaceous material and the intercellular spaces are small, containing air and some water. The crisp texture of fresh tissue is due to cell turgidity. Cell turgidity is "...a function of water absorbing power of the cell and the availability of water. The living cell is an osmotic system which maintains its turgor by literally 'sucking itself full of water'."(26) Appngaghgg Lg the mechanisms pf ggftgging. There have been three major approaches to the study of softening mechan- isms in plant tissue, chemical, physical, and histOIOgical. Branfoot (4), Carre (6), and Kertesz (15) have considered changes in pectin content and structure in the middle la- mella. McCready and Reeve (16), Reeve (20), and Reeve and Leinbach (21) have worked on the cellular changes in apples. Fabian (12) has modified basic procedures for examination of pickle tissues. Burstrom (5), Haines (13L Thoday (25), and many others have studied osmotic pressure relation to turgidity. In Kertesz's (15) review, he has stated that the true nature of the pectic material is not known. The pectic con- .tent exists not only in the middle lamella, but in the cell walls and in a dynamic state throughout the vacuole. Reeve and Leinbach (21) have pointed out that an analysis for pectin by the methods of Branfoot (4), Carre and Haynes (6), does not indicate the true pectic picture, and cannot be correlated with softening. Esau (8 ), Reeve (20), and Scott (22) have shown that the middle lamella contains other cell wall-encrusting materials such as cutins, suberins, lignins, hemicelluloses and proteinaceous material. .Reeve and Leinbach (21) state that "...the size of 'cells, intercellular spaces, and physiological conditions such as turgor pressure, are among the factors which in- fluence textural qualities in fresh tissues and which can also affect texture in processed tissues." Simpson and Halliday (24) have shown that in the steam- ing of carrots and parsnips, the pectin content is progres- sively lost with an increase in steaming time. However, their data is not directly relateable to softening or loss of criSpness. In contrast to this work, Boggs, et a1, (3) showed that boiling the seed coats of frozen peas for fif- teen minutes did not reduce the shear force necessary to penetrate the tissues. This may be due to the fact that pentosans rather than pectins form the incrustation of the seed coats. Haines (13),in a review of work on turgor and turgor pressure, has defined turgor as "rigidity resulting from distension". Turgor pressure was shown to be independent of environmental conditions, and the overall reaction at cell equilibrium was accepted as the diffusion potential of water outside the cell, or 00 + PC = Oe + Pa, where C8 = osmotic potential of the cell surroundings, CC = osmotic potential of the cell contents, P 2 environmental a pressure surrounding cell, and PC = hydrostatic pressure inside the cell. To illustrate the effects of the membrane on turgid- ity, Haines used the football as an analogy. "If a half inflated football is placed in a vacuum receiver and the pressure is lowered, the bladder will gradually expand... and the ball will become turgid... Similarly, if a fully inflated football has the environmental pressure increased, e.g. by taking [it] to the bottom of the sea, it will be- come flaccid." This analogy is of particular interest in processing. If a hot-filled container is closed and immersed in hot water, the pressure inside the container increases. Neg- lecting heat effects, this means that the cells experience an increase in pressure and become flaccid. Since the cells react to establish eouilibrium, they would lose water. when the container is cooled, there is a negative pressure (rel- ative to the atmosphere) and the cell should again become turgid. However, this picture is complicated by the pres- ence of brine, and the effects of heat on the permeability of the cell membrane. Disregarding heat effects, since 0 + P = O + P and 002 + P = O + Fag, where the subscripts 1, and 2, indicate before and after processing respectively, and since 001‘) cc“ and PC1I) E 2. Oc1 + P01 41’ must be greater than 002 + P09. that when the jar is opened to the atmosphere, the cells Therefore, we might suppose should be less turgid. From the preceeding, it is apparent that softening has been associated with at least four basic changes: 1. Cellular changes in shape, dimension, and wall thickness. 2. Intercellular changes in adsorbed gas and space voliune. 3. Pectic changes. 4. Changes due to osmotic effects. These conditions emphasize the fact that in attempting to measure changes in texture that occur as a result of heat processing, the parameters obtained are insufficient to des- cribe completely this complex phenomenon. However, the ne- cessity of evaluating quality objectively has promoted in- strumentation for objective analysis. Several types are described below. Objective Measurements of Softening in Plant Tissue Most of the instruments that have been developed for texture testing use one of the following measurements: 1. the force required to shear through the material 2. the force required to compress the material 3. the penetration of a plunger into the material under a given load for a specified time. The Magness-Taylor fruit pressure tester (a com- bination of #1 and #2) was developed for semi-hard, rela- tively large fruits such as apples. The Lee-Kramer shear- press measures, hydraulically, the pressure registered by passing a grid through a container of material such as green beans or other small fruits and vegetables. Several penetrometers have also been deveIOped for measuring the penetration rate into tissue. The recording strain gage denture tenderometer of Proctor, Davidson, Nalecki, and 10 Nelch (19) uses strain gages to sense the masticatory force simulated by human dentures. An oscillograph record shows the force penetration diagrams when the human chewing motion is approximated. This instrument and the modified shear- press (7 ) are the only two methods (to the author's know- ledge) that have been employed to show force-penetration diagrams in testing plant tissue. Softening of Pickles As previously mentioned, the producer of fresh cucum- ber pickles has been cautioned about overheating the product during pasteurization. The evidence to support this pre- caution has been limited to articles by Esselen et al., (10) and Jones, Etchells, Veldhuis, and Veerhoff (14). In the former article, concerned mainly with the pasteuriza- tion requirements of fresh pack pickles, the authors report that there is no significant heat-induced softening at process times up to 40 minutes at 1800 F. This conclusion was based on tests using the chatillon penetrometer-type jelly-strength tester with a 1/16 inch plunger to indicate firmness. Significant softening was determined by compar- ing the grams pressure required to penetrate k inch slices of the pickles with subjective evaluations. Pressures above 400 grams indicated firm pickles. Jones et alq(14) report that pasteurization of genuine dill pickles does not cause significant loss of firmness. However, pasteurization was accomplished by heating the 11 jars to a brine temperature of 1800F. and cooling immedi- ately: this heat treatment is substantially less than the recommended process time of Esselen and Anderson (59). The loss in firmness was measured with a U.S.D.A. fruit pressure tester with a 5/16 inch plunger. The only mathematical relationships reported on the ef- fect of different heat treatments on softening is by Nagel and Vaughn (1?). Their paper reviews methods for the ster- ilization of cucumbers for studies on microbial spoilage. Salt stock cucumbers were placed directly in a water bath and samples were removed at various intervals and examined for softening with the fruit pressure tester. Extensive softening was reported at temperatures above 1600 F. The rate of softening was reported to be the same regardless of the heating medium-~water or brine. Gas pockets were noted at temperatures above 160°F. (e.g. 1800 F. for 15 minutes). The pockets were thought to be due to the rapid evolution of gases present in the pickle. Plots of the logarithm of pressure versus time of heat- ing at temperatures of 1600 F., 1800 F., and 2000 F. were found to be linear, with a rapid decrease in pressure with temperature increase for the same heating time. EXPERIMENTAL Investigations were undertaken to determine the extent of heat softening in fresh cucumber dill pickles. For this purpose, a recording force-measuring device was designed to record the force-penetration pattern obtained when a plunger was forced through the pickle. With this instrument, the following tests were conducted on fresh and heat processed pickles. I. Apparatus Performance Tests A. Calibration B. Effect of vise tightening C. Multiple tests per pickle ED. Velocity and curve shape tests E. Tests on plungers II. Preliminary Storage Tests III. Heat Softening Tests IV. Methods Comparison Tests V. Tissue Removal Tests VI. Histological Tests The cucumbers used in this study were of mixed varie- ties, from different parts of Michigan, harvested at dif- ferent times in the season. These cucumbers were received during the course of the experiments in three lots and since variety, growing location, and time of harvesting may 13 have some influence on experimental results, each test was identified with a particular lot. Lot A, 3 bushels from the area near Mason, Michigan, was received during the first week in August and used in tests I, II, and VI. Lot B, 7 bushels from the Bay City, Michigan area, was received during the fourth week of August.and was used in test III. Iot C, 4 bushels from Croswell, Michigan, was received during the first week of September and used in tests IV and V. The cucumbers in all lots were of pickling varieties, predominantly SR-G, sizes ranging from 3 to 4 inches long and 1 to 1% inches in diameter. The cucumbers were received within sixteen hours of picking and processed within twenty-four hours of picking, unless otherwise in- dicated. Thirty cucumbers were selected from each bushel of each lot, and twenty cucumbers were chosen at random and tested for initial pressure. Treatment Prior to Heat Processing All lots received the same pre-process treatment unless otherwise indicated. The cucumbers were washed for five min- utes in cold (54° F.) water in an agitating washer and blanched in a 135° F. water bath for five minutes. The blanching was done in lots to minimize holding time between blanching and packing. Twenty-one ounces (1% ounce) of cucumbers were packed per quart Jar, and covering brine (135-1400 F.) was added, filling the jars to a head space 14 of %" (approximately eleven ounces of brine). The brine contained 1.4% acetic acid, 5.0% salt. One ml. of a 1 to 100 ml. dilution of dill spice oil #1 (courtesy of W. J. Stange Co.) was added to each Jar. The Jars were closed with screw-on lids. Heat Processing All Jars to be heat processed were totally immersed in an agitated, hot water bath, temperature controlled to i 10E (except those processed at 2110 F.). The Jars were placed in the bath within 3 minutes after covering with the hot brine. The temperature of the bath and the total heat processing time for each process are given in Table 1. Jars heated at 2110 F. were placed in boiling water. The Jars were cooled in a hot-water spray (1250 F.) for at least 2 minutes, followed by several minutes in a cool water spray. The time-temperature conditions in the Jars were sensed by copper-constantan thermocouples, located 5" from the bottoms of the Jars. Heating and cooling data were obtained for processing temperatures of 180°, 195°, and 2110 F. The tem- peratures were recorded on a twelve point one-cycle per min- ute temperature recording potentiometer; Ten quart Jars of pickles were heat processed for each set of time-temperature Iconditions of lots A, and B, 9 quarts for process numbers 21-24, and 2 quarts for process number 25 of lot C. 15 Table 1 - Heat processing of cucumbers Process L23 number Temperature, 3F. Time, min. A 1 180 30 2 210 30 B 3 160 60 4 160 720 5 160 1440 6 180 30 7 180 60 E 180 90 9 180 120 11:. 195 30 11 195 45 12 195 60 13 195 75 14 205 30 *3 205 35 ’L 205 45 1? 211 20 1C: 211 25 1? 211 30 20 211 42 C 21 180 30 22 180 120 23 210 25 24 210 3 25 No process -- Design and Operation of the Recording Pressure Tester The recording pressure tester (Figure 1) consists of five basic elements, the drive assembly, the sample holder, the testing plunger, the sensing device, and the recording instrument. A 1.91 rpm synchronous, gear-head motor (1) was mounted on the motor support (2) to bring the drive sprocket (3) in line with the pinion box Sprocket (4). When the 16 Fig. 1. The recording pressure teeter. 17 reversing switch (5) is in the down position, the motor shaft rotates the drive sprocket clockwise to move the rackshaft (6) through the pinion box (7). This forces the test plunger (8), at a constant velocity, into the pickle in the sample vise (9). The force required to penetrate the pickle is sensed by a Baldwin SR-4 load cell and the force is recorded by a Foxboro Dynalog M-40 recorder on a 12" circular chart. The range of the load cell and chart was 0-50 pounds, and the smallest division on the chart represents one pound force. When the chart drive toggle switch (11) is on, the chart rotates clockwise at 1 rpm, and the force is recorded versus plunger displacement. The maximum allowable load on the transducer is 70 lbs. force. To prevent overloading, there are three safety de- vices. The spring safety (12) contains a spring which is compressed to thirty pounds and is slotted to allow for further compression of the Spring when a force greater than thirty pounds is applied. The microswitch (13) roller fits the grooved microswitch contact sleeve (14); the switch is connected for normally Open Operation. When the contact is above or below the roller, the microswitch is Open. The length of travel of the test plunger is controlled by the length of the sleeve. A microswitch by-pass button permits machine Operation when the microswitch is Open. An addi- tional safety device is provided by using an adJustment of the force recorder. This is possible since the Foxboro —-A (Y) instrument is equipped with an electric on-off controlling device. Apparatus Performance Tests Lot A cucumbers, processed as indicated in Table 1, were used in the following tests. 1. Calibration of load cell and plunger velocity 2. Effect of vise tightening 3. Multiple tests per pickle 4 Velocity and curve shape tests 5. Tests on plungers A standard pickle testing procedure using the record- ' ing pressure tester was developed through tests 1-5, and used for all subsequent examinations. The sample was centered in the sample vise, and the vise tightened to contact (except in test 4). The vise plate was postioned so that the plun- ger would penetrate the pickle on the most prominent of the three lobes at a point equidistant from the stem and flower ends. A 3/8-inch diameter plunger with a flat head was used to penetrate the pickle at a velocity of 0.0682 inches per minute. This velocity was obtained by using a gear tooth ratio of 12:12 for the drive assembly sprockets. Typical curve shapes Obtained with this velocity are shown in Figure 2. One test was made on each pickle (except in test 5), and maximum force values were recorded unless PRESSURE, POUNDS 19 —205 ° F, 45 MIN. ——-195 °F, so MIN. —--—1sO°F, 60MIN. l J l l 0.1 CLZ 033 Ou4 0.5 PLUNGER DISPLACEMENT, INCHES Fig. 2. Typical curve shapes obtained using the recording pressure tester. 20 otherwise indicated. The load cell was calibrated by loading it with 1, 2, 5, 10, and 20 pound weights. The calibration indicated a 1 pound = 1.0 chart division displacement, linear over the range Of 0-20 pounds. Plunger diameters of 1/4" and 3/8" were tested using twenty pickles from a two-Jar composite of process 1, and a two-Jar composite Of process 2 (Table 1% A two-Jar composite indicates that pickles were chosen ran- domly from the total contents of the two Jars. The pickles were tested using the standard testing procedure, described above. Blades (%” x 1;" x 2" and 1/8" x 1%" x 2") were also tested in this manner: however, the pickles used had a di- ameter (approximately 1") smaller than the length of the cutting surface. Therefore, the end effects may have pro- duced the large deviations encountered. Although displacement of the plunger relative to the pickle is linearly related to angular pen travel on the re- corder chart, the moment of contact of the pickle by the plunger cannot be determined exactly. This uncertainty in the point of contact seems to be about 0.15 seconds before the pen rises above 0 pounds force. However, this condi- tion did not affect maximum force readings. The effect of tightening the sample vise was tested using a three-Jar composite of process 2. The three vise positibns tested were: 1. free movement-- no vise contact with pickle 21‘ 2. tightened to contact with pickle 3. tightened to contact plus two additional turns of the screw. The screw pitch is 0.063 inches; therefore, the pickles in position 3 were compressed .126 inches. Two Jars of process 1 were used to determine the effect of multiple punches per pickle. Three points were tested along the prominent lobe of the pickle in the following order: - 1. center 2. %” from stem end 3. g" from flower end. Maximum readings of punches for seven pickles in each of the two Jars were recorded. The effect Of plunger velocity on curve shape and max- imum pressure readings was tested using Lot C cucumbers. Ten pickles each from processes 21 and 24, and ten fresh cucum- bers were tested at each of three velocities with the re- cording pressure tester. Complete curves and maximum values were recorded. Velocities of 3.02, 6.55, and 14.2 inches per minute were attained with motor drive sprocket to pinion sprocket tooth ratios of 12:26, 12:12, and 26:12, respec- tively. Five plungers, all 1% inches in length were tested to determine the effect of plunger shape and diameter on the 22 force readings (Table 2). Fresh cucumbers (Lot C) were tested after 40 hours storage at 400 F. Ten cucumbers were used for each plunger test. Maximum values and curve shapes were recorded. Table 2 - Description Of plunger shapes Head radius of Head edge radius Plunger fig. Diameter, in. curvature, ig. g; curvature, Ag 1 3/8 0 o 2 3/8 1 2 _ o 3 3/8 1/2 1/8 4 3/8 1/2 0 5 5/16 1/4 1/16 Preliminary Storage Tests One bushel of fresh, unwashed cucumbers from Lot A was stored in a 400F., refrigerated box and tested upon receipt, after 16 and 40 hours storage, to determine the pressure loss for short-time storage. Twenty cucumbers were tested at each storage time. Twenty pickles from a three-Jar compos- ite of processes 1 and 2 were tested immediately after pro- cessing, after 16 and 40 hours storage, to examine the ex- tent Of softening for short-time storage of fresh cucumber dills. The Jars were stored at room temperature (75-80O F.L Heat Softening Tests Lot B pickles, processed as in Table 1, were stored at R) KN room temperatures (75-820 F.) for periods of twenty-four hours, three days, and five weeks. Twenty pickles from a two-Jar composite at each time-temperature combination were tested at each storage time. The storage time was measured from the time of removal from the processing water bath. Methods Comparison Tests The comparison tests were designed to show difference Obtained between subJective testing and pressure testing, using the fruit pressure tester and the recording pressure tester. For this purpose, twenty comparisons were made, consisting of four lots each from five sets of Jars at pro- cess conditions numbered 21, 22, 23, 24, 25 in Table 1. The twenty groups of approximately eighteen pickles each (from six Jar composites at each process) were divided into three subgroups of six pickles each. The three subgroups were used for the three methods comparisons, one subgroup for each method. In the subJective testing procedure, two pickles were given to each of the three Judges. They were told that one pickle was very soft and the other was very firm. Rating was on the basis of relative firmness on a 5—point hedonic scale. Values of 1, 2, 3, 4, 5, indicated very soft, soft, medium, firm, and very firm pickles respectively. Each Judge was then given two pans of pickles with four rows of five pickles in each pan. They were instructed to feel and 24 bite each pickle to determine firmness. Twenty pickles were positioned randomly in the pans: however, all Judges tested two pickles from each of the twenty lots--a total of forty pickles per Judge, or twenty-four pickles per set of pro- cessing conditions. Five pickles from each of the twenty lots were also tested with the fruit pressure tester. A 5/16H diameter, rounded plunger head was used in testing the pickles at the center of the prominent lobe. The pickles were placed on a flat surface and tested by pushing the plunger into the pickle, perpendicular to the surface. Five pickles from the third subgroup were tested using the standard testing procedure with the recording pressure tester. Maximum pressure readings were recorded. Tissue Removal Tests Twenty fresh cucumbers (stored seventy-two hours at 400 F.) were halved with a longitudinal cut through the prominent lobe and Opposing groove. Thirty halves were mixed randomly and tested with the recording pressure testen Ten were positioned in the vise with the seed cavity facing the plunger, ten with the seed cavity facing the base plate, and ten in the latter position with 500 microns of skin re- moved on the test area. The skin was removed on a section of the prominent lobe. The area of skin removed was se- lected so as to exclude warts. Maximum force readings were 25 recorded. Tissue resistance to penetration was examined in fresh and heat processed cucumbers by removing sucessive sections of tissue with a slide microtome and testing with the re— cording pressure tester. The pickles were tested whole, with % mm., 2.5 mm., and 10mm. of tissue removed. The five heat processing conditions and the number of pickles tested at each tissue removal depth are as follows: 1. fresh - 20 2. packed but given no heat process - 3 3. 180° F. for 30 minutes - 3 4. 1800 F. for 120 minutes - 2O 5 . 2100 F. for 35 minutes - 3. Histological Tests The purpose of the histological examinations was to examine cucumber tissue for gross anatomical changes due to the combined effects of heat and brine. These preliminary tests were conducted before pickling variety cucumbers were available: therefore, a slicing variety of cucumbers was used. The fresh cucumbers were blanched for five minutes at 1600 F., the ends were removed, and the remaining 4" lengths were quartered lengthwise. Seven-tenths of a pound was packed (skin towards center) in pint Jars, and a cov- ering brine (1.4% acetic acid by volume, 4.7% salt by weight) at a temperature of 135° F. was added to fill the Jars. The 26 Jars were sealed, and processed at 1650, 1700, and 1800 F. for two hours. Twelve Jars were processed at each tempera- ture in hot water baths, cooled in a warm water spray, dried and stored at 400 F. Heat penetration data was obtained for five Jars each at 1600 amd 1800 F. Tissue sections, approximately 250 microns thick, were taken from the parenchyma of pickles from each of three processes. The sections were stained with congo red and ex- amined under the microscOpe at 210 power. Gross changes in anatomical structure were noted. RESULTS The results are grouped according to the nature of the investigations. Group I includes tests on the Operation of the machine and comparison to other testing methods; group II includes tests on the raw product, short-time storage tests, and heat penetration studies; group III includes tests on the softening induced by heat processing. Group I - Machine Operation The three variables that were examined in Operating the recording pressure tester were velocity of plunger, plunger diameter, and vise tightening. Although only max- imum value readings of pressure were taken in most tests, the curve shapes (pressure versus displacement) were ana- lyzed in some tests as a characteristic of texture. The initial lepe (ascending) was considered to be the more in- formative of the slopes, since it was an indication Of the strain conditions of the pickle. The shape and magnitude of the descending slope was influenced by the plunger-head to plate distance and the diameter of the pickle. After the yield point had been reached (maximum force), the force recorded was dependent upon the thickness of the material compressed between the plunger head and the plate. For this reason, the micro-switch controller was adJusted to Open the motor drive circuit when the plunger head was i" from the plate. Further compression was found to load the cell beyond safe limits. The ascending slope of the force-penetration curve was not linear. The SIOpe consisted of a lag segment, which was highly irregular in shape, and a linear, or nearly linear segment (see Figure 2). For this reason, the SIOpe could not be measured accurately. Irregularities were noted as follows: 1. Small variations due to chain drive were no- ticed at all plunger velocities. 2. The SIOpe varied with degree of process: how- ever, no relationship was found. 3. The slope varied with velocity (Table 3). 4. A sharp break to increased slope was noticed for the plunger head velocity of 0.148 inches per minute. The variation in lepe with process mentioned above produced characteristic shapes of the force-penetration curve for each process. High values for slopes were no- ticed for pickles processed at relatively mild conditions. However, due to the non-linearity of the lepe, a relation- ship between sIOpe and heat process was not investigated. The change in slope with a change in velocity Of the plun- ger may be due to this non-linearity: however, the low 29 lepe value for .0314 inches per minute velocity with 1800 R, 30 minute processed pickles appears to be beyond the range of expected error (Table 3). Comparisons of the five plunger shapes show that the degree of "rounding" of a convex plunger head does not af- fect pressure readings. However, a concave shape does pro- duce significantly lower readings than a flat or convex shape (Table 4). This appears to be due to the sharper cutting edges of the concave head. The smaller (5/16") diameter plunger produced lower pressure readings than the standard 3/8" diameter plunger of the same shape. However, the pressure (calculated from force readings divided by plunger head area) recorded using the 5/16" diameter plun- ger was not significantly higher than that recorded using the 3/8" plunger. The 3/8" diameter, flat plunger was cho- sen for subsequent studies since it produced readings in the desired (1-20 pounds force) range for all processes. ty on ascending 1-13 3 - Fff’ t of “1; c i ”1:“: of icrce pone‘ra‘ion curve "“lccity Average lepe est orc: ;n/:-r. 112.11n. E'nre if slope ‘ ———-‘—_— ——-——— fresh .0314 46.6 44.6 - 51.0 1:35-30 min. .c31a 39.: 31.5 - L1.2 ."T2 48.? 44.9 - 51.6 .14:0 “130’: “.: - E107 30 Table 4 - Mean pressures obtained with various plunger shapes Average maximum Projected area Plunrer forceL lbs. of headL in.~ Pressure, psi 1 19.? 0.111 173 2 18.7 0.111 169 3 20.6 0.111 186 4 15.6 0.111 141 5 15.5 0.0765 203 Analysis of the vise tightening tests indicates that there is no significant difference in pressure readings at the degrees of tightening examined (Table 5). However, the low pressure readings and large standard deviations incurred in heat processing pickles may be clouding the true mean- ing of these results. The effect (not significant) indi- cated an increase in pressure with tightening. This seem logical since rigidity and lack of lateral eXpansion is en- countered with increasing tightening. Tightening to con- tact was selected for subsequent tests because at this po- sition, both lateral expansion and tightening distortion were minimized. Table 5 - Effect of vise position on force readings Kean value force Range of Vise position reading, pounds force readings open 3.9 1.5 - 5.0 tightened to contact 4.6 1.8 - 9.0 tightened to contact + .126” 5.0 1.8 - 8.8 Multiple-punch-per-pickle tests were conducted to es- tablish the pressure at three points on the most prominent lobe. Although there are six possible combinations in test- ing three points on the same pickle, only one combination was tested. An analysis of variance on the results of this 1 test indicates that there is a significant difference bet- ween the large and small end readings; however, the center test point a-pears to give an approximate average of the three readings (Table 6). For this reason, the center punch procedure was adOpted, and further tests on the dependence of pressure on order of testing multiple punches were not ex- amined. Table 6 — Effect of multiple tests per pickle on force readings Position Mean force, lbs. Range 9: values center 10.? 8.0 - 15.0 f10.I'v'eP end 902 790 "' 1300 Methods Comparison The data obtained in testing heat process scftening A F‘“ ("f r g. (f he recordin 1’ R pressure tester was compared with that 4.1 o a 4. ,. '1 - ,‘L m of tie iruit pressure tester and taste panel tesus. The 1 II 1 T» *d" ‘1 21 1»f1.‘*i:r "f :ignificcrt *2 ,aev ‘hrough- , i r: 0~ - 1.: i.- __ r’1,- ,0 a c . 1 , : _». ~ " a .x.- 7 ‘.: ,~ ifi -l - c - M f‘:~ . a 2’ ‘ significant ‘nuiéat 3 tie 1; level. 32 three tatsers selected had previous experience in tasting pickles for quality evaluations; however, they were not able to distinguish between the slight differences in softening indicated by the pressure testers (Table 7). Average values were recorded for the three judges; however, it was noticed that the judges were in closest agreement when testing firm pickles. From an analysis of these data, it appears that the Judges were not able to distinguish between processes that reduced the pressure below eleven pounds as tested by the recording pressure tester. Also, it appears that the thres— hold of difference in pressure (recording pressure tester) that was perceptible to these Judges was approximately three pounds for the range of 11-15 pounds. Table 7 - Results of comparison tests * Recording Fruit Process No. Panel scores pressure tester pressure tester mean range mean range mean range 25 4.2 3.0-4.8 15.4 15.0-15.9 12.8 12.0-133 21 3.7 3.2-4.0 14.3 14.0-14.7 11.4 11.3-116 22 2.7 2.0-3.5 11.4 10.9-12.0 9.0 8.9-9.3 23 2.6 2.0-3.0 10.0 19.9-10.4 6.6 6.5-6.7 24 2.2 1.7-2.8 6.1 5.6-6.3 4.9 4.8-5.1 See Table 1. 33 Mean values for the recording pressure tester and fruit pressure tester were compared to determine significant dif- ferences of processes as tested by each instrument. The means were correlated, and the regression was found to be linear with r = 0.997. The equation of the regression line (Figure 3) is y = 1.1x + 1.6, where y is pounds pressure measured by the recording pressure tester, and x is pounds pressure measured by the fruit pressure tester. The 1.6 in- tercept indicates a pressure difference that was attributed to the difference in the diameters of plunger heads. The ratio of the recording pressure tester plunger head to that of the fruit pressure tester was 1.44:1. This value is the expected lepe of the regression line if both apparatus test the same property in the same manner. However, the fruit pressure tester is subject to variations in reading caused by human variability in technique of testing. Group II - Tests on the Raw Product Fresh cucumbers, stored at 400 F. for sixteen hours, did not soften significantly. However, from sixteen to forty hours, there was a significant reduction in pressure. Pickles processed at 1800 - 30 minutes softened signifi- cantly (5% level) at sixteen hours storage at room temper- ature and there was also a significant reduction in pres- sure between sixteen and forty hours of storage. The aver- age initial fresh cucumber pressure was 16.2 pounds (Table 8). RECORDING PRESSURE TESTER FORCE,POUNDS RS <3 CD (D b 34 ;_____1% J4, L. l, l l 4 6 8 IO l2 1‘) FRUIT PRESSURE TESTER FORCE, POUNDS Fig. 3. Regression line for correlation of recording pressure tester with fruit pressure tester. Since significant softening occurred even at 400 F., all the cucumbers subsequently used in this study were processed as soon as practicable after receipt. Table 8 - Pressure of fresh cucumbers for short time storage Storage time Mean force Ragge 93 force hours pounds 0 16.2 1400-2005 Heat penetration Temperature measurements were made in five Jars at each of three temperatures, 1800 F., 1950 F., 2110 F. Heating and cooling curves were plotted, and equivalent minutes of each process in terms of minutes at processing temperature were based on the general method described by Bigelow, Bohart, Richardson, and Ball (2). The mean values of the heating rates, fh, and the lag factor, 1, are given in Table 9.1 Time-temperature data was not recorded for processing temperatures of 1600 and 205° F. Therefore, heat processing values at these tem- peratures were derived from the process values in Table 9. Since there was no significant difference for mean 3 values, an average 3 (0.884) was assumed for processes at 1600 and ' 2050 F. Analysis of variance showed that the mean fh values 1 See Appendix for definitions and heat process calculations. 36 were significantly different; therefore, the fh values for 1600 and 2050 F. were taken from a plot of fh against tem- perature (Figure 4). Table 9 - Heat processing values in fresh cucumber pickles Processing temperature, _§. Mean.fh, min. Mean 1 value 195 20.4 0.928 211 18.5 0.916 Group III - Heat Softening The 2 of softening was calculated by the method of iteration. A first approximation was made by plotting the process times corrected for an assumed z of 26° F. against pressure. The points of reduction to half the initial pres- sure taken from these curves were then plotted on semilog— arithmic coordinates against processing temperature. This second approximation suggests a z of about 35° F.; 2 values of 300 F. and 40° F. were used in a second, final calcula- tion of corrected process times. The assumed z of 300 F. was in agreement with the calculated z of 300 F. Table 10 gives the corrected process times based on a z of 30° F., and the corresponding recording pressure tester results for all processes at all three storage times. Fig- ure 5 shows the semi-logarithmic plot of pressure at three weeks'storage against equivalent minutes at processing 37 mo . mmnfimmazms ozammooma 2m: .mpdpmpmasou moammooopa paws mo godpousw a ma moms mcfipwmm .¢ .mfim O_N OON 0m. Om. Oh. cm. 0‘ 4 _ A _ ~ 0.0. l. 1m. H” w. 1| [ON H. O N fig 1 1_N H V I. H: .I’ I. no ,Nmnw / 4 .. I/ M I / 1 m [I mm mu // S , I T. / 1¢N I _ _ r _ p _ mm n.m s.m w._ ass m.m_ ma P_m m.w q.m m.m own a.» on ,_m ¢.__ o.m_ m.m 0mm o.m mm __m m.m_ s.m_ s.m oq_ w.m om aim _.m a.» m.s was o.¢m as mom o.m m.m m.m Pm; m.m_ mm mom s.m o.__ m.o_ own #:0. on mom w.m ©.~ m.m was o.nm ms mm_ m.m m.m m.» mom m.mm om mm. 0.0 _.o_ m.m mam w.nm m4 mm. F.m_ w.mp m.__ am? m.o_ on mm_ a.» m.mp q.> spa m.mm om_ ow_ a.m s.m. m.m awn m.mw om om, m._i o.¢_ s.oa mm_ m.mm ow om. m.¢c o.m_ a.m_ mm m.m_ on om_ m.b m.m ¢.o_ om¢_ om¢_ osa— \oo_ m.ma ¢.m_ ¢.m_ cos cos om» om_ o.m_ q.m_ w.¢_ ¢.o¢ ¢.o¢ om om? macs: w wasp m mason qm .cfis1admam .nfis .32 .Qastwosap .mo .oszpmaomamu mwsLOpm no swzdbmma mosow owwam>< mcofipfidcoO mmmooam mmaxoag sensuoso gmmam mo mwmhoum was msammmoopm 9mm: Log mmsdpwoa oopow mwmpm>¢ n or oprB temperature. Figure 6 was derived from Figure 5 by plot- ting the equivalent minutes at each processing temperature required to reduce the pressure to a common value, ten pounds. The reciprocal of the lepe of the curve in Fig- ure 6, z = 300 F., is in agreement with the assumed value of 30° F. The 3-week values were used in this analysis; however, there may still be further loss in pressure after three weeks of storage at room temperature. The 3-week storage period was chosen because these values were thought to be closer to the pressures after brine-pickle fluid equilibrium than the 24-hour or 5-day pressures. Plots similar to Fig- ure 5 for the 24-hour and 5-day pressures did not show a straight line relationship. Figure 5 indicates that the lines of best fit do not pass through the original pressure point, except for the 1800 F. line. This fact may be at- tributed to one or more of the following: 1. Over correction of process times. 2. Non-linearity of the relationship at short process times. 3. Non-random selection of cucumbers. Process times are over corrected because cold-point tem- peratures were used to adjust the process times, rather than an overall jar temperature. Departures from linearity could be brought about by effects other than heat, such as os- motic pressure differences between the covering brine and 1+0 20 I I I 1 FORCE, POUNDS N (D I l 0., N/ 0 °'. .‘n /o 06 "2 TI 5 o .41 1 o l 6L. (3 ._ 5—. .— 4__ _. 121m; 0 3 l l J J 20 4O 60 80 IOO EQUIVALENT MINUTES AT HEAT PROCESSING TEMPERATURE Fig" 5- Force readings at 3-weeks storage. 41 the natural cucumber fluids. Non-random selection of cucum- bers for testing may have occurred in some lots because in order to have enough cucumbers to complete the study, cucum- bers were packed that would not normally have been used. The values in Figure 6 indicate the minutes (UT) requi- red to obtain softening to ten pounds pressure at each proc- essing temperature. Ten pounds pressure was arbitrarily chos- en. If the logarithmic relationship between pressure and UT is assumed to be linear, any suitable reduction in pressure could have been used to obtain a 2 value. The z value obtained indicates that a 30°F. increase in temperature would decreas the equivalent processing time by a factor of ten for the same degree of softening. Figure 7 shows 3-week pressures plotted against corrected process times referred to equivalent minutes at 160°F. (Ffigo). If there is a z of softening, then a plot of the logarithm of 30 160 process should be a straight line. The data in Figure 7 fits pressure against equivalent minutes at 160°F (F ) for each well through about 350 minutes at 1600F., but the scatter becomes more marked at higher equivalent process times. A reference temperature for the presentation of Figure 7 of 160°F. was chosen to permit a comparison with pasteur- ization requirements deduced by Esselen, et. a1. ( ). Their suggested pasteurizing value, F160’ of 36 minutes is based on a z of 18°F. This recommended process time cannot be com- pared exactly to the data in this study, because at 36 min- utes (F150) the semilogarithmic relationship (Figure 5) does UT MINUTES FOR PRESSURE REDUCTION TO IOLBS. 42 ‘30 I T I I O 60 I— .— 40 —- ..._.I O 20 — fl IOr—- o .— 8 H ._.I 6 ~— 0 — 4 I I I I I70 180 I90 200 ZIO 220 HEAT PROCESSING TEMPERATURE °F Fig. 6. Pressure reduction to ten pounds as a function of heat processing temperature. POUNDS_ PRESSURE AT 3-WEEK STORAGE, 43 I I .7 I4 - (J —- -5 O- .q Cfi7a 9.. 3.. 7F- 5.. 5... O-I80°F. 4_ CI-l95’F. V-205°F. ‘1 Ch—2H°IE C) 3 I l l O 200 400 600 800 EQUIVALENT MINUTES AT 160° F. Fig. 7. 3-week storage pressures for heat processes in equivalent minutes at IGOOF. 44 not appear to hold at.this low process time. Figure 7 in- dicates that after 58 equivalent minutes at 1600F., the pressure reduction was less than 2 pounds. Tissue removal tests Pickles were halved and tested with the seed cavity facing the plunger, the base plate, and in the latter po- sition with the skin removed. Results of these tests in- dicated that the halves tested seed cavity facing down averaged 14.8 pounds force, whereas those tested seed cavity up averaged 5.7 pounds force. The former halves averaged 10.2 pounds force when_0.5 millimeters of tissue (roughly the depth of skin) was removed. These results suggested the hypothesis that if succesive sections of tissue were re- moved, the relative resistance to penetration of the sec- tions could be examined. The shin, two millimeters of supporting tissue, and the entire parenchymous section were removed. Results of these tests are illustrated in Figure 8. These data in- dicate that the resistance to penetration contributed by each tissue section is not the same for fresh and heat processed cucumbers. The underlying two millimeter section of fresh cucumbers was more resistant, and the 7.5 milli- meter section of the fresh cucumbers was less resistant to penetration. A comparison of loss in pressure curves (Figure 8) for C) .mGOAQomm m; n+0 .s nwseuut +J a“! .EZIJdSOme mamm; O_ m w v O _ 4 _ O s N I. mmhbzzz ON. I O I meow. Pd. ommmwoomm ~D ON bum: mmmmEDoDo IUI mmmmEDUDo Immmm I 1 O I I l 0 v °/.‘aanssaad N1 880’] l O (O Om fresh and heat processed cucumbers prompted the question of what the recording pressure tester actually tests. The curves and observations of the pickles during testing in- dicate that in pressure testing \J ’ a fresh cucumber is rigid and resists penetration with increasing force to a yield point, where the force required to penetrate further into the tissue rapidly approaches zero. In pressure testing cucumbers which have been moderately softened (to 11.4 pounds force), the resisting tissue is not rigid, and the area surrounding the plunger compressed with penetration; there is no yield point, but rather a yield zone of con- stant force with displacement. This suggests that shear force is a relatively more important factor in testing fresh cucumbers, whereas compression force is more no- ticeable in heat processed cucumbers. Histology Histological examinations were conducted on spears. The sections examined were relatively thick (250-300 mic- rons) and for this reason, only general observations were reported. The following changes were noted when the process temperature was increased from 1650 to 1800 F. (two hours processing time). 1. Cell walls were thinner and more irregular. 2. The intercellular spaces were larger. 3. There was a loss of intercellular gas. 4. Granulation of the nucleus was noted. DISCUSSION AND RECOKMENDATICNS A recording pressure tester was constructed and the variables of Operation were tested. From the results of these tests, a standard testing procedure was develOped. This procedure was compared with pressure testing, using the Magness-Taylor fruit pressure tester and subjective tex- ture testing. The recording pressure tester and the Magness- Taylor fruit pressure tester were correlated (r = .997) and these methods were shown to be more sensitive than a taste panel for measuring softening. Preliminary histological examinations were conducted to determine gross anatomical changes during heat proces- sing. These changes were cell wall thinning, loss in inter- cellular gas, enlargement of intercellular Spaces, loss of the turgid appearance of the cells, and granulation of the nucleus. These changes are in agreement with those reported in the literature. The relationship between heat induced softening and degree of heat processing was examined for storage periods of twenty-four hours, five days, and three weeks. The pressure at three weeks storage was found to approximate a logarithmic function of the equivalent minutes of proces- sing at bath temperature (UT). By plotting the time required 48 to reduce the pressure to a value of ten pounds in UT min- utes against temperature of processing bath, a z = 30° F. of softening was found. The pressure readings at twenty-four hours and five days storage did not obey the logarithmic function indicated at three weeks storage. After twenty—four hours storage, average pressures for each process were lower than at five days and three weeks storage. The five day storages pres- sure was higher than at twenty-four hours and three weeks. This fluctuation in pressure indicated that equilibrium pressure values had not been established after five days storage. It was thought that the low pressures at twenty- four hours might have been the result of low cell turgid- ity. This might have resulted from the relatively inelastic cell walls responding slowly to environmental changes in osmotic pressure. At five days storage, the cells might have reached maximum turgidity which decreased gradually on prolonged storage at room temperature. Therefore, it ap- peared that pressure reduction at three weeks storage was the result of both heat-induced softening and storage sof- tening. These results indicate that there would not be appre- ciable softening, regardless of processing temperature, if the cucumbers were heat processed to the recommended F160 value of thirty-six minutes. However, this conclusion was based on pressures obtained after three weeks of storage. 49 It is possible that heat induced changes in the structure and composititon of pickle tissues might result in more ex- tensive softening at prolonged storage. Further research is necessary to determine whether there are two distinct con- ditions, heat processing and storage, which cause soften- ing, or whether the latter is a function of the former. Section removal tests were conducted to indicate the resistance to penetration in the pickle tissues before and after processing. The zone of maximum resistance was found to be at a depth of 0.5-2.5 millimeters below the surface in fresh cucumbers. However, the skin (0.5 millimeters thick) constituted a zone of maximum resistance in pickles processed at 180° F. for thirty minutes. The percent loss in pressure beneath the skin to a depth of ten millimeters was shown to be linear with amount of tissue removed. These results, and observations of the pickles during testing in- dicated that the force readings in pressure testing fresh cucumbers were mainly due to shear, whereas the force read- ings for moderately soft (11.8 pounds force) pickles were mainly due to compression. This prompts the question of whether or not a pressure tester actually tests softness. The answer to this question lies in the unanswered question, what is softness? A recording pressure tester does indicate the force required to penetrate the tissue; whether this force is due to shear or to compression‘is not indicated. Perhaps what is needed is an instrument that differentiates Ln ‘2) between shear and compression. Recommendations The mechanism of softening is undoubtedly a complex set of physio-chemical phenomena. As has been pointed out previously, the contributing factors in loss of crispness are believed to include cell wall changes, turgidity, water relationships, and chemical changes related to cementing substances such as pectinaceous material. For this reason, it is impossible to determine the mechanism of.softening by means of an isolated physical constant of the product, such as pounds force required to penetrate the tissue. Although this work established a relationship between pressure as tested by the recording pressure tester and heat-induced softening in pickles, further investigation is recommended. There is a need for more extensive work to determine the mechanism of heat induced softening in relation to the anatomical changes in tissues. An analytical approach to this problem should include model systems simulating each of the suspected factors resulting in softening (for exam- ple, cell wall changes-~a histological approach). Recommendations based on an applied approach to the objective analysis of softening include more work in the area initiated in this paper, considering that the phenom- enon of softening is complex, it is better to study a single physical prOperty of that material that changes relative to m the processing conditions, rather than another complex of physical properties which may approximate a known condition such as chewing or crushing. A more careful analysis is needed of the results obtained using an instrument (such as the recording pressure tester) that is capable of testing a single physical content. It is possible that a modulus, such as Young's modulus can be obtained indicating the stress-strain condition of the product. A recording pressure tester could be used for this pur- pose. Young's modulus, Y = F/A + AL/L, where F is the force recorded using a plunger head area A, AL is the pene- tration of the plunger, and L is the pickle diameter. The slope of the force-penetration curve is the force per unit area divided by the penetration distance, AL. If the pic- kle diameter was measured, Young's modulus could be calcu- lated. There are two problems associated with testing Young's modulus in pickles. First, the force-penetration curve is not linear; and second, the force readings are not entirely the result of compression. Therefore, the record- ing pressure tester could be used to obtain Young's modulus only in products with negligible resistance to shear force. This would be the case in some semi-solid materials. Although pickles were the only product tested with the recording pressure tester, any product of suitable size and texture may be tested by varying the plunger size, velocity and vise capacity. Products can be compressed rather than 52 rather than penetrated by replacing the plunger with a plate; they may also be stretched and the deformations recorded as a function of time. APPENDIX The definitions and assumptions used in this study for heat process calculations of equivalent minutes are given below. Both the general method of Bigelow (2) and the for- mula method of Ball (1) were used. Definitions -E1 (-x) The value of the logarithmic integral -X et dt -. t fh SIOpe of the heat penetration curve, with log1O(Tfi-T) plotted against t It is the time required to tra- BO verse one log-cycle on this curve in minutes. g The difference between retort temperature (Th) and maximum temperature attained at processing time o tB O F. j The lag factor of the heat penetration curve, nu- “I merically equal to Th ' 10 Th - To Th Temperature of processing bath - O F. T0 Initial temperature, ° F. T5 Intercept on the time equals zero axis of the asymptote to the heat penetration curve tB Processing time, minutes T Temperature 0F. at time t B UT Equivalent minutes for a process at the heating temperature x A function of g and z by which the exponential in- tegral -Ei (-x) may be evaluated. x : loge210 g 2 Negative reciprocal of the lepe of the thermal death time curve, °F. 2 is a characteristic of bacterial destruction. The term 2 of softening is the negative reciprocal of the pressure reduction curve (Figure 7). “t The time required to destroy microorganisms at TOE r("1 Equivalence in minutes per minute of the process value at temperature T compared to one minute at -I — T -T Th. 1 .. 10 exp h Z Calculations of HT The general method was used for 180, 195, and 211° F. based on the five heat penetration curves at each temperature. '( -1 was calculated at one minute intervals frcm ii- heating curves up to the various process times. The sum of thet("I values gives the equivalent minutes contributed by the heating portion of the curve. The number of equivalent minutes con- tributed by the cooling portion of the curve appeared to be m m 0.5 minutes x flf-I, forwf"1 corresponding to each t The B' sum of the equivalent minutes contributed by the heating and cooling portions of the curve is UT' The maximum contribu- tion of the cooling portion was about 2% of the total equiva- lent minutes. As indicated in the text, the heating characteristics at 160 and 205°-F. were based on those at 180, 195, and 211° F. Ball's formula method was used to calculate the contribution of the heating portion of the curve to UT. The values of the eXponential integral was taken from the Jahnke, Emde tables. The equivalent minutes of the cooling portion of the curve was calculated as described above. The F?go equivalent minutes were calculated from U T minutes by: UT UT 10 exp (TE-T1/ z) I 30 7 — — O — o In this case LT — F160 , T1— 160 F., and z — 30 F. 10. 11. 12. REFERENCES Ball, C. 0. (1957). Sterilization lg Food Technology. flcGraw-Hill Inc. New York. 633 pp. Bigelow, W. D., G. S. Bohart, A. L. Richardson, and C. 0. Ball (1920). Heat penetration in processing canned foods. NCA Bull. 16-L. Boggs,M.M. H. Campbell, and C. D. Swartze (1942). Factons influencing the texture of peas preserved by freezing. Food Research. 7: 272. Branfoot, M. H. (1920). A critical and histological study of the pectic substances of plants. Dept. Sci. and Ind. Res. Food Inv. Sp. Report 33. Burstrom, H. (1948). A theoretical interpretation of turgor pressure. Phys. Plant. 1:57. Carre, M. H. and D. Haynes (1922). The estimation of pec- tin as calcium pectate and application of this method to the determination of soluble pectin in apples. Biochem J. 16:60-69. Decker, R. W., J. N. Yeatman, A. Kramer, and A. P. Sidwell (1950). Modifications of the shear-press for electrical indicating and recording. Food Tech. 11:343. Esau, K. (1953). Plant Anatomy. John Wiley and Sons, Inc. New York. 735 pp. Esselen, W. B. and E. E. Anderson (1952). Pasteurization of genuine dill pickles. Glass Packer. 31:600. Esselen, W. B., E. E. Anderson, L. F. Ruder, Jr., and I. J. Pflug (1951). Pasteurized fresh whole pickles. I. Pasteurization studies. Food Tech. 5:279. Etchells, J. L. and I. D. Jones (1944). Procedure for pasteurizing pickle products. Glass Packer. 23:519. Fabian, F. w. (1951). pp. 1888- 1936 in v. E. Jacobs, The Chemistry and Technology of Food and Food Products. Interscience Publishers, Inc. New York. 2 nd. _ed. 2580 g: 13. 14. 15. 16. 17. 22. 23. 57 Haines, F. M. (1953). An analysis of turgor and turgor pressure, Annals of Botany, N.S. 16:68. Jones, J. D., J. L. Etchells, M. K. Veldhuis, and O. Veerhoff (1941). Pasteurization of genuine dill pickles. Fruit Prod. J. 20:304. Kertesz, Z. I. (1951). The Pectic Substances. Inter- science Publishers Inc. New York. 628 pp. icCready, R. M. and R. M. Reeve (1955). Test for pectin based on reaction of hydroxamic acid with ferric ion. Jour. of Agr. and Food Chem. 3:260. Nagel, C. W. and R. H. Vaughn (1954). Sterilization of cucumbers for studies on microbial spoilage. Food Re- search. 19:613-616. Nutting, P. G. (1921). A new general law of deformation. Journal of the Franklin Institute. 191:679. Proctor, B. E., S. Davidson, G. J. Malecki, and M. A. Nelch (1955). Recording strain gage denture tenderometer for foods. I. Instrumentation, evaluation, and initial tests. Food Tech. 9:471. Reeve, R. M. (1953 . Histological investigations of tex- ture in apples. II. Structure and intercellular spaces. Food Research. 18:604. Reeve, R. M. and L. R. Leinbach (1953). Histological investigations of texture in apples. I. Composition and influence of heat on structure. Food Research. 18:592. Scott, F. M. (1950). Internal suberization of tissues. Bot. Gaz. 3:378-394. Scott-Blair, G. W. and F. M. V. Coppen (1942). The sub- jective conception of the firmness of soft material. Amerian Journal of Psychology. 55: 215-219. Simpson, J. I. and F. G. Halliday (1941). Chemical and histological studies of the disintegration of cell- membrane materials in vegetables during cooking. Food Research. 6:189-206. Thoday, D. (1952). Turgor pressure and wall pressure. Annals of Botany. N.S. 16:129. Meier, T. E. and C. R. Stocking (1949). Histological changes induced in fruits and vegetables by processing. Recent Advances in Food Research II. Academic Press. New York. 558 pp. MICHIGAN STAT E 31293 V 0 ER ITY I III II 4 7 034 UBRARES 2 “M 03