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Effect of Aseptic Processing on the Texture of Chicken Meat1
Effect of Aseptic Processing on the Texture of Chicken Meat 1 P. L. DAWSON, B. W. SHELDON,2 and J. J. MILES Department of Food Science, North Carolina State University, Raleigh, North Carolina 27695-7624 (Received for publication February 19, 1991)
1991 Poultry Science 70:2359-2367 INTRODUCTION
Aseptic heat processing is a high-temperature, short-time heating method used to render food safe from microbial pathogens and minimize negative effects on palatability as compared with traditional heat processing. Compared with traditional canning, aseptic processing not only reduces microbial loads but also minimizes the undesirable physical, chemical, and biological changes that are often associated with conventionally heat-processed foods (Swartzel, 1986). High-efficiency heat exchangers enable aseptic processors to deliver the heat treatment more rapidly and evenly throughout the food in comparison with the conventional canning operation. The tubular heat exchangers used in aseptic processing are ideally adapted to fluid foods such as milk,
'Paper Number FSR91-10 of the Journal Series of the Department of Food Science, North Carolina State University, Box 7624, Raleigh, NC 27695-7624. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service, nor criticism of similar ones not mentioned. The research reported in this publication was funded by the North Carolina Agricultural Service and the Center for Aseptic Processing and Packaging Studies. ^ o whom all correspondence should be addressed.
juice, pudding, and drinks; however, recent technological advances allow for the aseptic processing of food particulates. Foods such as soups, sauces, and stews often contain meat yet processors do not fully understand what the potential impact of aseptic processing will be on meat quality. Heating muscle food results in chemical and physical changes that will effect the texture, palatability, and consumer acceptance of the final product. The principal proteins responsible for meat texture include stromal (mostly collagen) and myofibrillar proteins (including myosin, actin, and actomyosin). Increased collagen content and collagen crosslinking in meat (often associated with older animals and specific muscle types) will increase the toughness of cooked meat (Swatland, 1984). Toughening can also result from myofibrillar protein shortening during heating. Dube et al. (1972) found that increased cooking temperatures used for beef myofibrillar protein extracts resulted in sarcomere shortening with maximum shortening detected at the highest temperatures evaluated (80 C). The objective of the present research was to determine the effect of aseptic processing on the texture, yield, and composition of two poultry meat sources.
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ABSTRACT Breast meat containing collagen at high concentrations (spent hen, 20 to 24 mo of age) and low concentrations (broiler, 6 to 7 wk of age) was evaluated for texture following high-temperature, short-time processing at 121, 130, and 145 C in a laboratory scale processing system. Breast meat was evaluated for proximate composition, collagen content, Kramer shear texture, Warner-Bratzler shear texture, and texture profile panel characteristics. Process parameters were adjusted across all processing temperatures to obtain a theoretical 12 logio population reduction of Clostridium botulinum spores. Aseptic processing resulted in significant moisture losses and toughening of the breast meat, which may be attributed to protein denaturation and myofibrillar shortening. Furthermore, the higher the processing temperature, the tougher and drier the meat and the lower the processing yields. Although the aseptic nightemperature, short-time process extracted and solubilized collagen, the process resulted in a tougher final meat texture. The profile panel identified seven texture characteristics that were significantly affected by aseptic processing. The total energy parameter of the Kramer shear test was significantly correlated to all seven texture characteristics identified by the panel. The results of the present study indicated that both hightemperature, short-time processing conditions and meat type significantly affected the proximate composition and textural characteristics of the finished product. (Key words: aseptic processing, spent hen, broiler, texture, high-temperature processing)
2360
DAWSON ET AL. MATERIALS AND METHODS
MEDIA OUTLET
Meat Source, Cooking, and Fabrication Procedures
Aseptic Processing Cooked breast strips were thawed in the Whirlpak bags at 4 C overnight and then processed in the Laboratory Scale Thermal Processing System and reactor cell (Figure 1). Twenty strips (~200-g loads) were placed in the reactor cell and mini-hypoderrnic, copper-constantan thermocouples (.02 cm diameter)4 were inserted into the center of three of the meat strips. The meat strips containing thermocouples were placed in a top, middle, and bottom position of the reactor cell to monitor any temperature variations within the cell. The cell was then filled with cold water before processing. The water inlet temperature of the processor was regulated by steam pressure. Water flow rate (950 rnL/min) and water back pressure [80 PSI (5.6 kg/cm2)] were held constant throughout
R C l R C 2 RC3
INLET
OUTLET
COMPUTER AND DATA COLLECTION
MEDIA INLET
FIGURE 1. Schematic of the Laboratory Scale Thermal Processing System. Abbreviations RCl, RC2, and RC3 represent reactor cell thermocouples. The chicken meat strips are represented by the rectangles inside the reactor cell.
processing. The circulating water inlet and outlet temperature of the processor and meat temperatures were monitored and recorded at 5-s intervals with an IBM personal computer using LabTech Notebook5 software. Equivalent processing time and temperature of the meat was calculated for each thermocouple using the Equivalent Point Method (Sadeghi et al, 1986). Typical processing run conditions are shown in Table 1. A theoretical 12 logio reduction of Clostridium botulinum spores were calculated for each meat thermocouple for each processing run using the activation energy (Ea) and preexponential constant (Ao) values of 74,115 cal and 2 x 1040, respectively (Diendoerfer and Humphrey, 1959). The log reductions were determined using the first order rate law C/Co = eKt, and the Arrhenius equation K = AeE^7 at time = t; where C = spore population; Co = spore population at Time 0; K =rate constant, t = equivalent processing time; R = the universal pressure constant; and T = equivalent processing temperature in Kelvin (279.16 + C). The Arrhenius value for K was used in the rate law formula to give C/C0 = et(AeX-Ea/RT>.
3
NASCO, Fort Atkinson, WI 53538. jOmega Engineering, Inc., Stamford, CT 06907. ^ b o r a t o r y Technologies Corporation, Wilmington, MA 01887.
The lnio of this equation results in the formula ln(C/Co) = tAe-Ea^T.
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Chilled, unfrozen spent Leghorn hen (20 to 24 mo of age at slaughter) and broiler (6 to 7 wk of age at slaughter) carcasses were obtained from a local supplier and transported to the university for testing. Hens and broilers were aged 2 to 3 days after slaughter before being cooked. Three hens and three broilers were used per replication and three repUcations were used per experiment. Prior to aseptic processing, hen and broiler carcasses were cooked in a 95 C common water bath (steam-jacketed kettle) to an internal temperature of 80 C. After cooking, carcasses were placed in a 4 C cooler and chilled overnight. The following day carcasses were skinned and the breasts excised. The excised Pectoralis superficialis muscles were cut parallel to the muscle fiber into 2 x 2 x 6 cm strips, then randomly selected for packaging in Whirlpak bags,3 and then frozen and held at -20 C. Chicken strips were held frozen 2 to 3 days prior to aseptic processing. The maximum number of breast strips as feasible were fabricated from each breast while maintaining longitudinal fiber orientation and the specified dimensions.
2361
ASEPTIC PROCESSING OF CHICKEN
Proximate Composition and Processing Yield
il
Percentage moisture, fat, and protein were determined for raw, cooked, and cooked then aseptically processed meat using American Association of Official Analytical Chemists (1984) procedures. The processing yield by weight of aseptically processed meat was determined using the formula
111
SiCS
30.8
1
u
Percentage meat yield =
_
rt
.-<
Collagen Analysis
3© 3t- 8«s
Collagen content of the meat was determined using the procedure described by Burson and Hunt (1986). Soluble and insoluble collagen were separated by heating ground samples for 70 min at 77 C in one-quarter strength Ringers solution (32.75 mM NaCl, 1.5 mM KC1, .5 mM CaCl2), and then centrifuged (12,100 x g, 15 min). The pellet was reextracted and the two supernatants pooled. The pellet and pooled supernatants were analyzed separately for hydroxyproline and expressed as either insoluble or heat-soluble collagen fractions, respectively. The hydroxyproline content of the two fractions were expressed as a percentage of the total hydroxyproline from the supernatant and pellet residue. Total collagen was determined by multiplying the hydroxyproline content by 7.25 (Goll et aU 1964).
c s *•« *-<
u
o o N oo
I
Instrumental Shear Testing Multiple-Blade Shear. Five-gram samples were cut from the meat strips and sheared perpendicular to the muscle fiber length using a 10-blade Kramer shear press6 mounted on a Model 1122 Instron Universal Testing Machine.7 Shear samples were cut from the strips into approximately 2 x 2 x 1 cm pieces to weigh approximately 5.0 g. The operating parameters consisted of a crosshead speed of 100 mm/min, a 500-kg load cell, and a full scale range of 200 kg. The force-deformation curve and area under the curve were recorded on an Instron recorder7
^odel CS-l; Food Technology Coip., Rockville, MD 20852. 7 Instron Corp., Canton, MA 02021.
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weight after aseptic processing X 100. weight before aseptic processing
t^
M- oo >n o\ od \o
2362
DAWSON ET AL. TABLE 2. Chicken texture terminology and grading scales used in texture profile panels and for statistical analysis
Stage
Action
Variable tested Elasticity — degree to which the sample returns to original shape after deformation.
n
Initial — place sample approximately 2 cm into mouth, compress partially between incisors, release and evaluate for: First bite — place sample into mouth with the fibers perpendicular to the teeth, bit with incisors approximately 2 cm from the end and evaluate for:
First bite — place a sample into the mouth with the fibers parallel to the teeth, bite with incisors and evaluate for: Mastication — chew a 2 x 2 x 2 cm sample with the molar teeth and evaluate for:
(500 mm/min chart speed) and integrator, respectively. Peak force at failure (PkF) and total energy or work (Ej) were determined and expressed on a per gram basis (Case, 1988). Single-Blade Shear. Breast strips (11 x 11 x 60 mm) were sheared perpendicular to the muscle fiber length using a Wamer-Bratzler shear apparatus7 mounted on a Model 1122 Instron Universal Testing Machine.7 A crosshead speed of 200 mm/min was used along with a 50-kg load cell and a full scale range of 10 kg. The peak force was recorded on an Instron recorder7 (100 mm/min chart speed). Texture Profile Panel The texture profile analysis was conducted using a six member professional panel (Civille and Szczesniak, 1973). The panel members identified and defined the order of perception for each of the texture character notes summarized in Table 2. Frozen breast meat strips representing the four treatments (cooked broiler, aseptically processed broiler, cooked hen, and aseptically processed hen) were thawed to 4 C overnight and then heated in boiling bags for 10 min in a 90 C water bath. Samples were held on a warming tray prior to testing. Each treatment
Hardness across the grain — force required to compress the sample (to get the teeth together) as much as possible. Moisture Release 1 — the degree the sample releases juices at first bite. Cohesiveness — the degree the sample deforms between teeth. Hardness with the grain — force required to compress the sample (to bring the teeth together) as much as possible. Chewiness — number of chews required to prepare the sample for swallowing, working at a steady rate of one chew per second. Oiliness — amount of oil or fat in the juices. Moisture Release 2 — amount of juices released during chewing. Cohesiveness of the mass — degree to which the mass is holding together at 10 to 12 chews. Fibrousness — degree to which fibers felt in the mouth persist throughout mastication.
was assigned a three-digit random code and presented to the panelists in random order. The cooked broiler breast meat was used as a reference standard and only meat processed at 130 C was tested by the panel due to previous results indicating that 145 C produced unpalatable meat. A 14-point descriptive and 10-point overall impression scale were utilized and converted to 14-point and 10-point numeric scales, respectively, for statistical analysis. Experimental Design and Statistical Analysis The study was divided into two experiments. The objectives of Experiment 1 were to evaluate me effect of two meat sources, broiler (low collagen content) and spent hen meat (high collagen content) aseptically processed at three temperatures (121,130, and 145 C), on processing yields, proximate composition, and instrumental texture of the meat. Unprocessed samples that were cooked served as controls and will be identified as cooked samples. Based on the results of Experiment 1, the 130 C processing temperature was chosen for further testing in Experiment 2, which monitored collagen content, texture profiles, and instrumental texture characteristics.
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m
a
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ASEPTIC PROCESSING OF CHICKEN
TABLE 3. The percentage of moisture, fat, protein, and processing yield of cooked, unprocessed, and cooked, aseptically processed broiler and spent hen chicken breast meat Dry Sample1
Moisture
Protein
fat2
Dry protein
Yield
C"!T\
Cooked broiler Broiler 145 C Broiler 130 C Broiler 121 C Cooked hen Hen 145 C Hen 130 C Hen 121 C
66.4a 63.5C 64.9 b 65.6 ab 66.1 a 58.7* 61.3 d 63.2°
31.l e 33.8C 32.5d 31.9^ 31.4 e 38.6a 36.1 b 34.3C
6.5a 5.8b 6.0 b 6.1 b 6.8a 5.8 b 5.9 b 6.0 b
92.5b 92.6b 92.6b 92.7b 92.6b 93.5a 93.3a 93.2 a
85.5b 91.0 s 92.0" 74.6d 79.6° 81.0°
a_e
Approximately 12 to 14 meat strips per hen moment correlation and significant probabilities from four carcasses and 8 to 10 strips per broiler test (SAS Institute, 1982). from 10 carcasses were pooled and randomized within meat type. Twenty randomly selected RESULTS AND DISCUSSION strips per treatment per replicate were selected for each aseptic treatment. Thus, bird to bird Experiment 1 variation was not tested for in die experimental design. The research was analyzed as two Processing Yields. Broiler breast meat had a separate experiments and both experiments were significantly higher yield at the 130 C procesreplicated three times. Three observations per sing temperature (91.0%) with lower variation treatment per replicate were taken for collagen, (SD = 2.6%) than spent hen breast meat (79.6%, shear, and proximate analysis. Seven observa- SD = 4.4%) (data not shown, n = 3). Processing tions per treatment per replicate were recorded yield decreased to 74.6% for hen meat when the for the texture panel analysis (six panel scores media processing temperature was increased to and one panel consensus score). Experiment 1 145 C. However, no significant difference in was analyzed by ANOVA (SAS Institute, 1982) yield was observed within hen or broiler meat using a split-plot design with the main effect of types processed at 130 and 121 C. The yield meat source (broiler and spent hen) being split differences detected at 145 C were primarily due into four aseptic treatments (cooked, 121 C, 130 to significant moisture losses. The percentage of C, and 145 C). The replication by meat source fat and protein remained constant or increased interaction served as die whole plot error term slightly due to moisture losses. The range of whereas the replication by meat source by moisture losses across process temperatures was aseptic treatment interaction was used as the .8 to 2.9% for broiler meat and 2.9 to 7.4% for subplot error term. Experiment 2 was analyzed hen meat. Hen meat averaged 3.8% more with a General Linear Model using a random- moisture loss than broiler meat. ized complete block design. Meat source treatMoisture, Fat, and Protein. The proximate ments (broiler and spent hen) and the aseptic composition of the cooked broiler and hen breast treatments (cooked and 130 C aseptic process) meat were not significantly different (Table 3). were the main effects. Experiment 2 was Higher aseptic processing temperatures resulted replicated three times and the replication by in significantly more moisture loss. In general, treatment interaction was used as the error term. increased processing temperatures should result When F values were significant, means were in more denaturation of myofibrillar proteins separated using Duncan's multiple range test. and loss of water binding potential. Under the The texture panel results were correlated to the conditions of the present study, acceptable instrumental texture data (Kramer and Wamer- yields and meat texture were not achieved with a Bratzler shear) using the Pearson product- processing temperature of 145 C.
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Means within columns with no common superscripts are significantly different (P<05). n = 9. 121 C, 130 C, and 145 C represent the aseptic processing media temperature tested. Dry weight basis.
2364
DAWSON ET AL.
cantly more deformable than broiler meat The decreased moisture content of the meat at the higher processing temperature would result in a drier, chewier texture. Experiment 2 Collagen Content. Cooked hen meat contained significantly higher total collagen than cooked broiler meat (Table 5). Differences in collagen content between the two meat sources can be attributed to differences in the approximate age of the birds at the time of slaughter (broiler = 6 to 7 wk, hen = 20 to 24 mo) (Swatland, 1984). The aseptic processing treatment significantly reduced the total collagen content of the hen meat by 27.3% (milligram per gram of meat basis) but the broiler meat was not significantly affected. These differences in collagen content, due to meat source and aseptic processing, remained when the total collagen content was expressed on a per gram of protein basis. The loss of hen meat total collagen in the processed samples, when expressed on a per gram of protein basis, indicates that collagen was extracted by the aseptic processing of hen meat. Cooked hen meat had significantly less (11.52%) heat soluble collagen than broiler meat (Table 5). This is not surprising because the heat solubility of collagen decreases with increased collagen crosslinMng and crosslinking increases as the animal ages (Swatland, 1984). Therefore, older hens would have a higher total collagen content that is more crosslinked than the
TABLE 4. The peak force per gram, total energy, energy to failure, and Warner-Bratzler single blade peak force for cooked and aseptically processed broiler and spent hen chicken meat Warner3
Kramer2,3 Sample Cooked broiler Broiler 145 C Broiler 130 C Broiler 121 C Cooked hen Hen 145 C Hen 130 C Hen 121 C a-e
Peak force d
8.1 13.7b 10.8* 8.3 d 9.4 cd 17.6" 14.3b 13J b
Total energy 381
e
nd**
691° 63^ 524 d 1,183" 851 b 800b
Energy to failure
Peak force
11.2d 13.0° 12.3C 11.2d 14.3b 16.0s 1S.21* 14.0b
2.6 d
52'b
4.0 bc 32a 45" 6.1" 4.7 b 3.4^
Means with no common superscripts within columns are significantly different (P<05). n = 9. 121 C 130 C, and 145 C represent the aseptic processing media temperature tested. ^Denotes the Kramer multiple-blade shear compression cell test and the Warner-Bratzler single-blade shear test Kramer peak force is reported as kilograms of force per gram of meat, total energy and energy to failure is reported in millimeters by kilogram, and Warner peak force is reported as kilogram force per 1-cm x 1-cm cross section of meat
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Fat was also extracted during processing. When expressed on a dry weight basis, the fat content was significantly lower in the aseptically processed meat than the cooked meat (Table 3). The dry weight protein content did not significantly differ between cooked and aseptically processed broiler meat but did in the two hen treatments. Because the meat was cooked in water prior to aseptic processing, the majority of the sarcoplasmic proteins would have been extracted, leaving the myofibrillar and stromal fractions as the major protein components. Instrumental Texture. Both the Kramer shear compression and the Warner-Bratzler shear peak force values reflect a greater toughness across all processing temperatures for spent hen meat in comparison with broiler meat (Table 4). Meat toughness also increased with an increase in aseptic processing media temperature. At 145 C, the Kramer peak force values were 87 and 69% higher than the hen and broiler controls, respectively. The Warner-Bratzler shear test confirmed the toughening effect observed in the Kramer shear peak force and total energy values. Both shear techniques showed similar differences in toughness due to aseptic processing, indicating that both methods may be suitable for monitoring aseptically processed chicken meat texture. The energy to failure parameter is an indicator of deformability of the meat The greater the energy to failure, the more deformable Gess brittle) the sample is before it fails (breaks). Higher aseptic processing temperatures resulted in a more deformable meat sample. Furthermore, hen meat was signifi-
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ASEPTIC PROCESSING OF CHICKEN
TABLE 5. Total collagen and percentage of heat-soluble collagen in cooked, unprocessed and cooked, aseptically processed broiler and spent hen chicken breast meat Sample
Cooked broiler Processed broiler1 Cooked hen Processed hen'
Total collagen
Total collagen
Soluble collagen
(mg/g meat)
(mg/g protein)
(% of total)
1.73° 1.71° 3.44" 2.50b
5.56° 5.23c 10.96" 6.89b
28.73 b 38.25" 17.21c 39.92"
"""Means with no common superscripts within columns are significantly different (P<05). n 'Aseptically processed at 130 C.
panel for the cooked hen meat in comparison with the drier aseptically processed hen and broiler meat. Aseptically processed hen meat required significantly more chews to prepare for swallowing man the aseptically processed broiler and cooked hen meat. Both the aseptically processed broiler and cooked hen meat were perceived as being more oily and less fibrous than the aseptically processed hen. The fat content between samples was not significantly different; however, differences in texture and moisture content may have given the aseptically processed hen meat the perception of being less oily. The dryness and higher collagen content of the aseptically processed hen meat may have contributed to its increased fibrousness. The Et and PkF/g values were significantly correlated to several texture panel characteristics (Table 7). However, the Warner-Bratzler shear results did not correlate with any texture panel
TABLE 6. Texture profile panel means for cooked spent hen and aseptically processed hen and broiler chicken breast meat (cooked broiler was scored as a blind reference) Texture parameter'
Aseptically processed broiler
Cooked hen
Aseptically processed hen
Hardness across the grain Moisture release 1 Hardness with the grain Chewiness Oiliness Moisture release 2 Fibrousness
11.3b 2.4 b 8.6b 41.0 b 1.7* 2.3 b 11.3b
10.3C 2.9" 6.7" 40.1 b 2.0" 3.6" 11.l b
12.6" 2.0b 10.3" 45.7" 1.3b 1.9° 12.1"
"""Means with no common superscripts within rows are significantly different (P<.05). n = 21. 'Hardness across the grain = force required to compress the sample (to get the teeth together) as much as possible; Moisture Release 1 = the degree the sample releases juices; Cohesiveness = the degree the sample deforms between teem; Hardness with the grain=force required to compress the sample (to bring the teeth together) as much as possible; Chewiness =number of chews required to prepare the sample for swallowing, working at a steady rate of one chew per second; Oiliness = amount of oil or fat in the juices; Moisture Release 2 = amount ofjuices released during chewing; Cohesiveness of the mass = degree to which the mass is holding together at 10 to 12 chews; and Fibrousness = degree to whichfibersfelt in the mouth persist throughout mastication.
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younger broilers. Furthermore, aseptic processing significantly increased the percentage of soluble collagen in broiler (33.1% increase) and hen (132% increase) meat compared with cooked breast meat. Texture Profile Panel. The texture profile panelists evaluated the cooked hen meat and the cooked, aseptically processed hen and broiler meat. The cooked broiler meat was used as a reference by the panel during each test session. Of the 10 texture parameters evaluated, 7 were significantly influenced by treatment (Table 6). The results of the two sensory hardness parameters (across and with the grain) supported the instrumental texture results indicating that aseptic processing toughened the meat. The aseptically processed hen meat was significantly tougher man the aseptically processed broiler meat. This toughening may be related to greater collagen crosslinking in the hen meat. A greater release of moisture (1 and 2) was detected by the
9.
2366
DAWSON ET AL. TABLE 7. Correlation coefficients of instrumental texture testr with texture panel characteristics of aseptically processed broiler and spent hen breast meat Kramer shear cell
Texture panel characteristics2
Peak force
Total energy
Collagen content
Hardness across the grain Moisture release 1 Hardness with the grain Chewiness Oiliness Moisture release 2 Fibrousness
+.91** -.87** +.93** +.63 -.75* -.97** +.47
+.95** -.87** +.87** +.66* -.89** -.94** +.66*
-.47 +.53 -.56 -.17 +.38 +.69* -.06
1
characteristics for the cooked and aseptically processed chicken meat. The purpose for correlating the panel results with instrumental tests was to determine which, if any, tests can be used to predict specific texture panel characteristics. The Ej parameter was significantly correlated to all seven of the texture characteristics that were significantly affected by aseptic processing. The PkF/g value was significantly correlated to five of seven texture notes but collagen content was significantly correlated with only Moisture Release 2. Collagen content in meat has been shown to be directly related to toughness, fibrousness, and chewiness of meat (Swatland, 1984). However, the aseptic temperatures tested in the present study toughened the meat, overshadowing any tenderizing effect expected by the reduction of total collagen and insoluble collagen from aseptic processing. The cooked hen meat contained more collagen than the aseptically processed hen meat but was perceived as being more tender and required less force to shear. The aseptically processed broiler meat was tougher than the cooked broiler meat but was still more tender than the cooked hen meat. Both aseptic processing and higher collagen content due to the meat source contributed to the toughening, although their individual contributions to toughening cannot be separated because aseptic processing resulted in lower collagen contents.
Collagen content was not a good predictor of aseptically processed meat texture. In summary, although the aseptic process used in this study solubilized and reduced collagen content, the process also toughened the chicken meat. The 145 C media processing temperature toughened the meat and reduced processing yields more than the 130 and 121 C media temperatures. Aseptic processing temperatures below 145 C are also recommended to minimize toughening. Although both the Warner-Bratzler and Kramer shear tests discriminated between aseptic temperature treatments, only the Kramer test measurements were significantly correlated to texture profile panel characteristics. This suggests that the Kramer test is the better method to distinguish between specific texture notes identified by a trained profile panel. REFERENCES Association of Official Analytical Chemists, 1984. Official Methods of Analysis. 14th ed. Association of Official Analytical Chemists, Arlington, VA. Burson, D. E., and M. C. Hunt, 1986. Heat induced changes in the proportion of Types I and HI collagen in bovine longissimus dorsi. Meat Sci. 17:153-160. Case, S., 1988. The effect of starch gelatinization on the texture of extruded wheat and com products. M.S. thesis, North Carolina State University, Raleigh, NC. Civille, G. V., and A. S. Szczesniak, 1973. Guidelines to training a texture profile panel. J. Texture Stud. 4: 204-223.
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Only instrumental tests that were significantly correlated to textural panel characteristics are presented. Warner-Bratzler shear test and the Kramer energy to failure values were not significantly correlated to any texture panel characteristics. 2 Hardness across the grain = force required to compress the sample (to get the teeth together) as much as possible; Moisture Release 1 = the degree the sample releases juices; Cohesiveness = the degree the sample deforms between teeth; Hardness with the grain = force required to compress the sample (to bring the teeth together) as much as possible; Chewiness =number of chews required to prepare the sample for swallowing, working at a steady rate of one chew per second; Oiliness = amount of oil or fat in the juices; Moisture Release 2 = amount of juices released during chewing; Cohesiveness of the mass = degree to which the mass is holding together at 10 to 12 chews; and Fibrousness = degree to which fibers felt in the mouth persist throughout mastication. *P<.05. **P<.01.
ASEPTIC PROCESSING OF CHICKEN Diendoerfer, F. H., and A. E. Humphrey, 1959. Microbiological process discussion: Principles in the design of continuous sterilizers. Appl. Microbiol. 7:264-270. Dube, G., V. D. Brambett, M. O. Judge, and R. B. Harrington, 1972. Physical properties and sulphydryl content of bovine muscle. J. Food Sci. 37:23-29. Goll, D. E., W. G. Hoekstra, and R. W. Bray, 1964. Ageassociated changes in bovine muscle connective tissue. I. Rate of hydrolysis by collagenase. J. Food Sci. 29: 608-614. Sadeghi, F., M. H. Hamid-Samini, and K. R. Swartzel, 1986.
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Micro-computer program for determining the unique time-temperature associated with the equivalent point method of thermal evaluation. J. Food Process. Preserv. 10:331-335. SAS Institute, 1982. SAS® User's Guide: Statistics. 1982 Edition. A. A. Ray, ed. SAS Institute, Inc., Cary, NC. Swartzel, K., 1986. Equivalent point method for thermal evaluation of continuous-flow systems. J. Agric. Food Chem. 34:396^*02. Swatland, H., 1984. Structure and Development of Meat Animals. Prentice-Hall, Inc., Englewood Cliffs, NJ.
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1991 Poultry Science 70:2359-2367 INTRODUCTION
Aseptic heat processing is a high-temperature, short-time heating method used to render food safe from microbial pathogens and minimize negative effects on palatability as compared with traditional heat processing. Compared with traditional canning, aseptic processing not only reduces microbial loads but also minimizes the undesirable physical, chemical, and biological changes that are often associated with conventionally heat-processed foods (Swartzel, 1986). High-efficiency heat exchangers enable aseptic processors to deliver the heat treatment more rapidly and evenly throughout the food in comparison with the conventional canning operation. The tubular heat exchangers used in aseptic processing are ideally adapted to fluid foods such as milk,
'Paper Number FSR91-10 of the Journal Series of the Department of Food Science, North Carolina State University, Box 7624, Raleigh, NC 27695-7624. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service, nor criticism of similar ones not mentioned. The research reported in this publication was funded by the North Carolina Agricultural Service and the Center for Aseptic Processing and Packaging Studies. ^ o whom all correspondence should be addressed.
juice, pudding, and drinks; however, recent technological advances allow for the aseptic processing of food particulates. Foods such as soups, sauces, and stews often contain meat yet processors do not fully understand what the potential impact of aseptic processing will be on meat quality. Heating muscle food results in chemical and physical changes that will effect the texture, palatability, and consumer acceptance of the final product. The principal proteins responsible for meat texture include stromal (mostly collagen) and myofibrillar proteins (including myosin, actin, and actomyosin). Increased collagen content and collagen crosslinking in meat (often associated with older animals and specific muscle types) will increase the toughness of cooked meat (Swatland, 1984). Toughening can also result from myofibrillar protein shortening during heating. Dube et al. (1972) found that increased cooking temperatures used for beef myofibrillar protein extracts resulted in sarcomere shortening with maximum shortening detected at the highest temperatures evaluated (80 C). The objective of the present research was to determine the effect of aseptic processing on the texture, yield, and composition of two poultry meat sources.
2359
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ABSTRACT Breast meat containing collagen at high concentrations (spent hen, 20 to 24 mo of age) and low concentrations (broiler, 6 to 7 wk of age) was evaluated for texture following high-temperature, short-time processing at 121, 130, and 145 C in a laboratory scale processing system. Breast meat was evaluated for proximate composition, collagen content, Kramer shear texture, Warner-Bratzler shear texture, and texture profile panel characteristics. Process parameters were adjusted across all processing temperatures to obtain a theoretical 12 logio population reduction of Clostridium botulinum spores. Aseptic processing resulted in significant moisture losses and toughening of the breast meat, which may be attributed to protein denaturation and myofibrillar shortening. Furthermore, the higher the processing temperature, the tougher and drier the meat and the lower the processing yields. Although the aseptic nightemperature, short-time process extracted and solubilized collagen, the process resulted in a tougher final meat texture. The profile panel identified seven texture characteristics that were significantly affected by aseptic processing. The total energy parameter of the Kramer shear test was significantly correlated to all seven texture characteristics identified by the panel. The results of the present study indicated that both hightemperature, short-time processing conditions and meat type significantly affected the proximate composition and textural characteristics of the finished product. (Key words: aseptic processing, spent hen, broiler, texture, high-temperature processing)
2360
DAWSON ET AL. MATERIALS AND METHODS
MEDIA OUTLET
Meat Source, Cooking, and Fabrication Procedures
Aseptic Processing Cooked breast strips were thawed in the Whirlpak bags at 4 C overnight and then processed in the Laboratory Scale Thermal Processing System and reactor cell (Figure 1). Twenty strips (~200-g loads) were placed in the reactor cell and mini-hypoderrnic, copper-constantan thermocouples (.02 cm diameter)4 were inserted into the center of three of the meat strips. The meat strips containing thermocouples were placed in a top, middle, and bottom position of the reactor cell to monitor any temperature variations within the cell. The cell was then filled with cold water before processing. The water inlet temperature of the processor was regulated by steam pressure. Water flow rate (950 rnL/min) and water back pressure [80 PSI (5.6 kg/cm2)] were held constant throughout
R C l R C 2 RC3
INLET
OUTLET
COMPUTER AND DATA COLLECTION
MEDIA INLET
FIGURE 1. Schematic of the Laboratory Scale Thermal Processing System. Abbreviations RCl, RC2, and RC3 represent reactor cell thermocouples. The chicken meat strips are represented by the rectangles inside the reactor cell.
processing. The circulating water inlet and outlet temperature of the processor and meat temperatures were monitored and recorded at 5-s intervals with an IBM personal computer using LabTech Notebook5 software. Equivalent processing time and temperature of the meat was calculated for each thermocouple using the Equivalent Point Method (Sadeghi et al, 1986). Typical processing run conditions are shown in Table 1. A theoretical 12 logio reduction of Clostridium botulinum spores were calculated for each meat thermocouple for each processing run using the activation energy (Ea) and preexponential constant (Ao) values of 74,115 cal and 2 x 1040, respectively (Diendoerfer and Humphrey, 1959). The log reductions were determined using the first order rate law C/Co = eKt, and the Arrhenius equation K = AeE^7 at time = t; where C = spore population; Co = spore population at Time 0; K =rate constant, t = equivalent processing time; R = the universal pressure constant; and T = equivalent processing temperature in Kelvin (279.16 + C). The Arrhenius value for K was used in the rate law formula to give C/C0 = et(AeX-Ea/RT>.
3
NASCO, Fort Atkinson, WI 53538. jOmega Engineering, Inc., Stamford, CT 06907. ^ b o r a t o r y Technologies Corporation, Wilmington, MA 01887.
The lnio of this equation results in the formula ln(C/Co) = tAe-Ea^T.
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Chilled, unfrozen spent Leghorn hen (20 to 24 mo of age at slaughter) and broiler (6 to 7 wk of age at slaughter) carcasses were obtained from a local supplier and transported to the university for testing. Hens and broilers were aged 2 to 3 days after slaughter before being cooked. Three hens and three broilers were used per replication and three repUcations were used per experiment. Prior to aseptic processing, hen and broiler carcasses were cooked in a 95 C common water bath (steam-jacketed kettle) to an internal temperature of 80 C. After cooking, carcasses were placed in a 4 C cooler and chilled overnight. The following day carcasses were skinned and the breasts excised. The excised Pectoralis superficialis muscles were cut parallel to the muscle fiber into 2 x 2 x 6 cm strips, then randomly selected for packaging in Whirlpak bags,3 and then frozen and held at -20 C. Chicken strips were held frozen 2 to 3 days prior to aseptic processing. The maximum number of breast strips as feasible were fabricated from each breast while maintaining longitudinal fiber orientation and the specified dimensions.
2361
ASEPTIC PROCESSING OF CHICKEN
Proximate Composition and Processing Yield
il
Percentage moisture, fat, and protein were determined for raw, cooked, and cooked then aseptically processed meat using American Association of Official Analytical Chemists (1984) procedures. The processing yield by weight of aseptically processed meat was determined using the formula
111
SiCS
30.8
1
u
Percentage meat yield =
_
rt
.-<
Collagen Analysis
3© 3t- 8«s
Collagen content of the meat was determined using the procedure described by Burson and Hunt (1986). Soluble and insoluble collagen were separated by heating ground samples for 70 min at 77 C in one-quarter strength Ringers solution (32.75 mM NaCl, 1.5 mM KC1, .5 mM CaCl2), and then centrifuged (12,100 x g, 15 min). The pellet was reextracted and the two supernatants pooled. The pellet and pooled supernatants were analyzed separately for hydroxyproline and expressed as either insoluble or heat-soluble collagen fractions, respectively. The hydroxyproline content of the two fractions were expressed as a percentage of the total hydroxyproline from the supernatant and pellet residue. Total collagen was determined by multiplying the hydroxyproline content by 7.25 (Goll et aU 1964).
c s *•« *-<
u
o o N oo
I
Instrumental Shear Testing Multiple-Blade Shear. Five-gram samples were cut from the meat strips and sheared perpendicular to the muscle fiber length using a 10-blade Kramer shear press6 mounted on a Model 1122 Instron Universal Testing Machine.7 Shear samples were cut from the strips into approximately 2 x 2 x 1 cm pieces to weigh approximately 5.0 g. The operating parameters consisted of a crosshead speed of 100 mm/min, a 500-kg load cell, and a full scale range of 200 kg. The force-deformation curve and area under the curve were recorded on an Instron recorder7
^odel CS-l; Food Technology Coip., Rockville, MD 20852. 7 Instron Corp., Canton, MA 02021.
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weight after aseptic processing X 100. weight before aseptic processing
t^
M- oo >n o\ od \o
2362
DAWSON ET AL. TABLE 2. Chicken texture terminology and grading scales used in texture profile panels and for statistical analysis
Stage
Action
Variable tested Elasticity — degree to which the sample returns to original shape after deformation.
n
Initial — place sample approximately 2 cm into mouth, compress partially between incisors, release and evaluate for: First bite — place sample into mouth with the fibers perpendicular to the teeth, bit with incisors approximately 2 cm from the end and evaluate for:
First bite — place a sample into the mouth with the fibers parallel to the teeth, bite with incisors and evaluate for: Mastication — chew a 2 x 2 x 2 cm sample with the molar teeth and evaluate for:
(500 mm/min chart speed) and integrator, respectively. Peak force at failure (PkF) and total energy or work (Ej) were determined and expressed on a per gram basis (Case, 1988). Single-Blade Shear. Breast strips (11 x 11 x 60 mm) were sheared perpendicular to the muscle fiber length using a Wamer-Bratzler shear apparatus7 mounted on a Model 1122 Instron Universal Testing Machine.7 A crosshead speed of 200 mm/min was used along with a 50-kg load cell and a full scale range of 10 kg. The peak force was recorded on an Instron recorder7 (100 mm/min chart speed). Texture Profile Panel The texture profile analysis was conducted using a six member professional panel (Civille and Szczesniak, 1973). The panel members identified and defined the order of perception for each of the texture character notes summarized in Table 2. Frozen breast meat strips representing the four treatments (cooked broiler, aseptically processed broiler, cooked hen, and aseptically processed hen) were thawed to 4 C overnight and then heated in boiling bags for 10 min in a 90 C water bath. Samples were held on a warming tray prior to testing. Each treatment
Hardness across the grain — force required to compress the sample (to get the teeth together) as much as possible. Moisture Release 1 — the degree the sample releases juices at first bite. Cohesiveness — the degree the sample deforms between teeth. Hardness with the grain — force required to compress the sample (to bring the teeth together) as much as possible. Chewiness — number of chews required to prepare the sample for swallowing, working at a steady rate of one chew per second. Oiliness — amount of oil or fat in the juices. Moisture Release 2 — amount of juices released during chewing. Cohesiveness of the mass — degree to which the mass is holding together at 10 to 12 chews. Fibrousness — degree to which fibers felt in the mouth persist throughout mastication.
was assigned a three-digit random code and presented to the panelists in random order. The cooked broiler breast meat was used as a reference standard and only meat processed at 130 C was tested by the panel due to previous results indicating that 145 C produced unpalatable meat. A 14-point descriptive and 10-point overall impression scale were utilized and converted to 14-point and 10-point numeric scales, respectively, for statistical analysis. Experimental Design and Statistical Analysis The study was divided into two experiments. The objectives of Experiment 1 were to evaluate me effect of two meat sources, broiler (low collagen content) and spent hen meat (high collagen content) aseptically processed at three temperatures (121,130, and 145 C), on processing yields, proximate composition, and instrumental texture of the meat. Unprocessed samples that were cooked served as controls and will be identified as cooked samples. Based on the results of Experiment 1, the 130 C processing temperature was chosen for further testing in Experiment 2, which monitored collagen content, texture profiles, and instrumental texture characteristics.
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m
a
2363
ASEPTIC PROCESSING OF CHICKEN
TABLE 3. The percentage of moisture, fat, protein, and processing yield of cooked, unprocessed, and cooked, aseptically processed broiler and spent hen chicken breast meat Dry Sample1
Moisture
Protein
fat2
Dry protein
Yield
C"!T\
Cooked broiler Broiler 145 C Broiler 130 C Broiler 121 C Cooked hen Hen 145 C Hen 130 C Hen 121 C
66.4a 63.5C 64.9 b 65.6 ab 66.1 a 58.7* 61.3 d 63.2°
31.l e 33.8C 32.5d 31.9^ 31.4 e 38.6a 36.1 b 34.3C
6.5a 5.8b 6.0 b 6.1 b 6.8a 5.8 b 5.9 b 6.0 b
92.5b 92.6b 92.6b 92.7b 92.6b 93.5a 93.3a 93.2 a
85.5b 91.0 s 92.0" 74.6d 79.6° 81.0°
a_e
Approximately 12 to 14 meat strips per hen moment correlation and significant probabilities from four carcasses and 8 to 10 strips per broiler test (SAS Institute, 1982). from 10 carcasses were pooled and randomized within meat type. Twenty randomly selected RESULTS AND DISCUSSION strips per treatment per replicate were selected for each aseptic treatment. Thus, bird to bird Experiment 1 variation was not tested for in die experimental design. The research was analyzed as two Processing Yields. Broiler breast meat had a separate experiments and both experiments were significantly higher yield at the 130 C procesreplicated three times. Three observations per sing temperature (91.0%) with lower variation treatment per replicate were taken for collagen, (SD = 2.6%) than spent hen breast meat (79.6%, shear, and proximate analysis. Seven observa- SD = 4.4%) (data not shown, n = 3). Processing tions per treatment per replicate were recorded yield decreased to 74.6% for hen meat when the for the texture panel analysis (six panel scores media processing temperature was increased to and one panel consensus score). Experiment 1 145 C. However, no significant difference in was analyzed by ANOVA (SAS Institute, 1982) yield was observed within hen or broiler meat using a split-plot design with the main effect of types processed at 130 and 121 C. The yield meat source (broiler and spent hen) being split differences detected at 145 C were primarily due into four aseptic treatments (cooked, 121 C, 130 to significant moisture losses. The percentage of C, and 145 C). The replication by meat source fat and protein remained constant or increased interaction served as die whole plot error term slightly due to moisture losses. The range of whereas the replication by meat source by moisture losses across process temperatures was aseptic treatment interaction was used as the .8 to 2.9% for broiler meat and 2.9 to 7.4% for subplot error term. Experiment 2 was analyzed hen meat. Hen meat averaged 3.8% more with a General Linear Model using a random- moisture loss than broiler meat. ized complete block design. Meat source treatMoisture, Fat, and Protein. The proximate ments (broiler and spent hen) and the aseptic composition of the cooked broiler and hen breast treatments (cooked and 130 C aseptic process) meat were not significantly different (Table 3). were the main effects. Experiment 2 was Higher aseptic processing temperatures resulted replicated three times and the replication by in significantly more moisture loss. In general, treatment interaction was used as the error term. increased processing temperatures should result When F values were significant, means were in more denaturation of myofibrillar proteins separated using Duncan's multiple range test. and loss of water binding potential. Under the The texture panel results were correlated to the conditions of the present study, acceptable instrumental texture data (Kramer and Wamer- yields and meat texture were not achieved with a Bratzler shear) using the Pearson product- processing temperature of 145 C.
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Means within columns with no common superscripts are significantly different (P<05). n = 9. 121 C, 130 C, and 145 C represent the aseptic processing media temperature tested. Dry weight basis.
2364
DAWSON ET AL.
cantly more deformable than broiler meat The decreased moisture content of the meat at the higher processing temperature would result in a drier, chewier texture. Experiment 2 Collagen Content. Cooked hen meat contained significantly higher total collagen than cooked broiler meat (Table 5). Differences in collagen content between the two meat sources can be attributed to differences in the approximate age of the birds at the time of slaughter (broiler = 6 to 7 wk, hen = 20 to 24 mo) (Swatland, 1984). The aseptic processing treatment significantly reduced the total collagen content of the hen meat by 27.3% (milligram per gram of meat basis) but the broiler meat was not significantly affected. These differences in collagen content, due to meat source and aseptic processing, remained when the total collagen content was expressed on a per gram of protein basis. The loss of hen meat total collagen in the processed samples, when expressed on a per gram of protein basis, indicates that collagen was extracted by the aseptic processing of hen meat. Cooked hen meat had significantly less (11.52%) heat soluble collagen than broiler meat (Table 5). This is not surprising because the heat solubility of collagen decreases with increased collagen crosslinMng and crosslinking increases as the animal ages (Swatland, 1984). Therefore, older hens would have a higher total collagen content that is more crosslinked than the
TABLE 4. The peak force per gram, total energy, energy to failure, and Warner-Bratzler single blade peak force for cooked and aseptically processed broiler and spent hen chicken meat Warner3
Kramer2,3 Sample Cooked broiler Broiler 145 C Broiler 130 C Broiler 121 C Cooked hen Hen 145 C Hen 130 C Hen 121 C a-e
Peak force d
8.1 13.7b 10.8* 8.3 d 9.4 cd 17.6" 14.3b 13J b
Total energy 381
e
nd**
691° 63^ 524 d 1,183" 851 b 800b
Energy to failure
Peak force
11.2d 13.0° 12.3C 11.2d 14.3b 16.0s 1S.21* 14.0b
2.6 d
52'b
4.0 bc 32a 45" 6.1" 4.7 b 3.4^
Means with no common superscripts within columns are significantly different (P<05). n = 9. 121 C 130 C, and 145 C represent the aseptic processing media temperature tested. ^Denotes the Kramer multiple-blade shear compression cell test and the Warner-Bratzler single-blade shear test Kramer peak force is reported as kilograms of force per gram of meat, total energy and energy to failure is reported in millimeters by kilogram, and Warner peak force is reported as kilogram force per 1-cm x 1-cm cross section of meat
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Fat was also extracted during processing. When expressed on a dry weight basis, the fat content was significantly lower in the aseptically processed meat than the cooked meat (Table 3). The dry weight protein content did not significantly differ between cooked and aseptically processed broiler meat but did in the two hen treatments. Because the meat was cooked in water prior to aseptic processing, the majority of the sarcoplasmic proteins would have been extracted, leaving the myofibrillar and stromal fractions as the major protein components. Instrumental Texture. Both the Kramer shear compression and the Warner-Bratzler shear peak force values reflect a greater toughness across all processing temperatures for spent hen meat in comparison with broiler meat (Table 4). Meat toughness also increased with an increase in aseptic processing media temperature. At 145 C, the Kramer peak force values were 87 and 69% higher than the hen and broiler controls, respectively. The Warner-Bratzler shear test confirmed the toughening effect observed in the Kramer shear peak force and total energy values. Both shear techniques showed similar differences in toughness due to aseptic processing, indicating that both methods may be suitable for monitoring aseptically processed chicken meat texture. The energy to failure parameter is an indicator of deformability of the meat The greater the energy to failure, the more deformable Gess brittle) the sample is before it fails (breaks). Higher aseptic processing temperatures resulted in a more deformable meat sample. Furthermore, hen meat was signifi-
2365
ASEPTIC PROCESSING OF CHICKEN
TABLE 5. Total collagen and percentage of heat-soluble collagen in cooked, unprocessed and cooked, aseptically processed broiler and spent hen chicken breast meat Sample
Cooked broiler Processed broiler1 Cooked hen Processed hen'
Total collagen
Total collagen
Soluble collagen
(mg/g meat)
(mg/g protein)
(% of total)
1.73° 1.71° 3.44" 2.50b
5.56° 5.23c 10.96" 6.89b
28.73 b 38.25" 17.21c 39.92"
"""Means with no common superscripts within columns are significantly different (P<05). n 'Aseptically processed at 130 C.
panel for the cooked hen meat in comparison with the drier aseptically processed hen and broiler meat. Aseptically processed hen meat required significantly more chews to prepare for swallowing man the aseptically processed broiler and cooked hen meat. Both the aseptically processed broiler and cooked hen meat were perceived as being more oily and less fibrous than the aseptically processed hen. The fat content between samples was not significantly different; however, differences in texture and moisture content may have given the aseptically processed hen meat the perception of being less oily. The dryness and higher collagen content of the aseptically processed hen meat may have contributed to its increased fibrousness. The Et and PkF/g values were significantly correlated to several texture panel characteristics (Table 7). However, the Warner-Bratzler shear results did not correlate with any texture panel
TABLE 6. Texture profile panel means for cooked spent hen and aseptically processed hen and broiler chicken breast meat (cooked broiler was scored as a blind reference) Texture parameter'
Aseptically processed broiler
Cooked hen
Aseptically processed hen
Hardness across the grain Moisture release 1 Hardness with the grain Chewiness Oiliness Moisture release 2 Fibrousness
11.3b 2.4 b 8.6b 41.0 b 1.7* 2.3 b 11.3b
10.3C 2.9" 6.7" 40.1 b 2.0" 3.6" 11.l b
12.6" 2.0b 10.3" 45.7" 1.3b 1.9° 12.1"
"""Means with no common superscripts within rows are significantly different (P<.05). n = 21. 'Hardness across the grain = force required to compress the sample (to get the teeth together) as much as possible; Moisture Release 1 = the degree the sample releases juices; Cohesiveness = the degree the sample deforms between teem; Hardness with the grain=force required to compress the sample (to bring the teeth together) as much as possible; Chewiness =number of chews required to prepare the sample for swallowing, working at a steady rate of one chew per second; Oiliness = amount of oil or fat in the juices; Moisture Release 2 = amount ofjuices released during chewing; Cohesiveness of the mass = degree to which the mass is holding together at 10 to 12 chews; and Fibrousness = degree to whichfibersfelt in the mouth persist throughout mastication.
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younger broilers. Furthermore, aseptic processing significantly increased the percentage of soluble collagen in broiler (33.1% increase) and hen (132% increase) meat compared with cooked breast meat. Texture Profile Panel. The texture profile panelists evaluated the cooked hen meat and the cooked, aseptically processed hen and broiler meat. The cooked broiler meat was used as a reference by the panel during each test session. Of the 10 texture parameters evaluated, 7 were significantly influenced by treatment (Table 6). The results of the two sensory hardness parameters (across and with the grain) supported the instrumental texture results indicating that aseptic processing toughened the meat. The aseptically processed hen meat was significantly tougher man the aseptically processed broiler meat. This toughening may be related to greater collagen crosslinking in the hen meat. A greater release of moisture (1 and 2) was detected by the
9.
2366
DAWSON ET AL. TABLE 7. Correlation coefficients of instrumental texture testr with texture panel characteristics of aseptically processed broiler and spent hen breast meat Kramer shear cell
Texture panel characteristics2
Peak force
Total energy
Collagen content
Hardness across the grain Moisture release 1 Hardness with the grain Chewiness Oiliness Moisture release 2 Fibrousness
+.91** -.87** +.93** +.63 -.75* -.97** +.47
+.95** -.87** +.87** +.66* -.89** -.94** +.66*
-.47 +.53 -.56 -.17 +.38 +.69* -.06
1
characteristics for the cooked and aseptically processed chicken meat. The purpose for correlating the panel results with instrumental tests was to determine which, if any, tests can be used to predict specific texture panel characteristics. The Ej parameter was significantly correlated to all seven of the texture characteristics that were significantly affected by aseptic processing. The PkF/g value was significantly correlated to five of seven texture notes but collagen content was significantly correlated with only Moisture Release 2. Collagen content in meat has been shown to be directly related to toughness, fibrousness, and chewiness of meat (Swatland, 1984). However, the aseptic temperatures tested in the present study toughened the meat, overshadowing any tenderizing effect expected by the reduction of total collagen and insoluble collagen from aseptic processing. The cooked hen meat contained more collagen than the aseptically processed hen meat but was perceived as being more tender and required less force to shear. The aseptically processed broiler meat was tougher than the cooked broiler meat but was still more tender than the cooked hen meat. Both aseptic processing and higher collagen content due to the meat source contributed to the toughening, although their individual contributions to toughening cannot be separated because aseptic processing resulted in lower collagen contents.
Collagen content was not a good predictor of aseptically processed meat texture. In summary, although the aseptic process used in this study solubilized and reduced collagen content, the process also toughened the chicken meat. The 145 C media processing temperature toughened the meat and reduced processing yields more than the 130 and 121 C media temperatures. Aseptic processing temperatures below 145 C are also recommended to minimize toughening. Although both the Warner-Bratzler and Kramer shear tests discriminated between aseptic temperature treatments, only the Kramer test measurements were significantly correlated to texture profile panel characteristics. This suggests that the Kramer test is the better method to distinguish between specific texture notes identified by a trained profile panel. REFERENCES Association of Official Analytical Chemists, 1984. Official Methods of Analysis. 14th ed. Association of Official Analytical Chemists, Arlington, VA. Burson, D. E., and M. C. Hunt, 1986. Heat induced changes in the proportion of Types I and HI collagen in bovine longissimus dorsi. Meat Sci. 17:153-160. Case, S., 1988. The effect of starch gelatinization on the texture of extruded wheat and com products. M.S. thesis, North Carolina State University, Raleigh, NC. Civille, G. V., and A. S. Szczesniak, 1973. Guidelines to training a texture profile panel. J. Texture Stud. 4: 204-223.
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Only instrumental tests that were significantly correlated to textural panel characteristics are presented. Warner-Bratzler shear test and the Kramer energy to failure values were not significantly correlated to any texture panel characteristics. 2 Hardness across the grain = force required to compress the sample (to get the teeth together) as much as possible; Moisture Release 1 = the degree the sample releases juices; Cohesiveness = the degree the sample deforms between teeth; Hardness with the grain = force required to compress the sample (to bring the teeth together) as much as possible; Chewiness =number of chews required to prepare the sample for swallowing, working at a steady rate of one chew per second; Oiliness = amount of oil or fat in the juices; Moisture Release 2 = amount of juices released during chewing; Cohesiveness of the mass = degree to which the mass is holding together at 10 to 12 chews; and Fibrousness = degree to which fibers felt in the mouth persist throughout mastication. *P<.05. **P<.01.
ASEPTIC PROCESSING OF CHICKEN Diendoerfer, F. H., and A. E. Humphrey, 1959. Microbiological process discussion: Principles in the design of continuous sterilizers. Appl. Microbiol. 7:264-270. Dube, G., V. D. Brambett, M. O. Judge, and R. B. Harrington, 1972. Physical properties and sulphydryl content of bovine muscle. J. Food Sci. 37:23-29. Goll, D. E., W. G. Hoekstra, and R. W. Bray, 1964. Ageassociated changes in bovine muscle connective tissue. I. Rate of hydrolysis by collagenase. J. Food Sci. 29: 608-614. Sadeghi, F., M. H. Hamid-Samini, and K. R. Swartzel, 1986.
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Micro-computer program for determining the unique time-temperature associated with the equivalent point method of thermal evaluation. J. Food Process. Preserv. 10:331-335. SAS Institute, 1982. SAS® User's Guide: Statistics. 1982 Edition. A. A. Ray, ed. SAS Institute, Inc., Cary, NC. Swartzel, K., 1986. Equivalent point method for thermal evaluation of continuous-flow systems. J. Agric. Food Chem. 34:396^*02. Swatland, H., 1984. Structure and Development of Meat Animals. Prentice-Hall, Inc., Englewood Cliffs, NJ.
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