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Nonfat Dry Milk Inhibits Pink Discoloration in Turkey Rolls1
PROCESSING AND PRODUCTS Nonfat Dry Milk Inhibits Pink Discoloration in Turkey Rolls1 B. N. DOBSON2 and D. P. CORNFORTH3 Department of Nutrition and Food Sciences, Utah State University, Logan, Utah 84322-8700
1992 Poultry Science 71:1943-1946
INTRODUCTION A pink discoloration is frequently observed on cut surfaces of cooked turkey rolls, and it is often interpreted by consumers as an indication of undercooking. Nitrite contamination of meat or ingredients is seldom the source of the problem. Hemochromes have been associated with pink color of turkey rolls (Cornforth et al, 1986) and canned tuna (Brown and Tappel, 1957). Hemochromes may develop under anaerobic conditions from the reaction of reduced heme and various nitrogenous groups, including amino side chains of denatured proteins (Cornforth et al., 1986; Ann and Maurer, 1990). Potassium iodate, an oxidizing agent, inhibits pink discoloration in cooked turkey meat (Cornforth et al, 1986), but is not acceptable for commercial use. Milk proteins, especially calcium caseinate, have been promoted for their
Received for publication March 31, 1992. Accepted for publication July 1, 1992. ^Authors appreciate the support of the Western Dairy Foods Research Center for this study. Journal Paper Number 4298 of the Utah Agricultural Experiment Station. 2 Present address: Golden Cheese Co. of California, 1138 West Rincon Street, Corona, CA 91720. 3 To whom correspondence should be addressed.
whitening effect in chicken nuggets formulated with thigh meat or mechanically deboned chicken (van den Hoven, 1987). Nonfat dried milk (NFDM) has been reported to lighten the color of bologna (Rongey and Bratzler, 1966). Milk proteins may also alleviate pink discoloration in poultry. The present study determined whether two dried milk protein products, NFDM and whey protein concentrate (WPC), affected the incidence of pink discoloration in turkey rolls. MATERIALS AND METHODS Formulation and Processing Turkey rolls (2.8 kg per treatment) were formulated to contain breast meat (90%), thigh meat (10%), water and ice (10%), internal or cluster fat (10%), salt (1%), and NFDM or WPC (3%), expressed as percentage of total meat weight (breast and thigh meat = 2.3 kg per treatment). Control (C) rolls were formulated without milk proteins. Frozen meat obtained from a regional processor was tempered overnight, then passed through a 2.5-cm plate before further processing. The possible effects of particle size and fat emulsification on color were evaluated by making turkey rolls from finely chopped meat emulsions (E), finely chopped meat and pre-emulsified fat (PE), or from coarsely ground meat (CG).
1943
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 27, 2015
ABSTRACT Pink discoloration in turkey rolls was prevented by incorporating 3% nonfat dry milk (NFDM) in the formulation. Coarsely ground, cooked turkey rolls formulated with NFDM also had higher levels of undenatured myoglobin than did controls. Nonfat dry milk may inhibit formation of reduced heme-denatured globin pigments (globin hemochromes) in cooked meat by inhibiting myoglobin denaturation or promoting heme oxidation. The mechanism of inhibition of pink discoloration by NFDM remains to be determined. (Key words: turkey, meat, color, myoglobin, nonfat dry milk)
1944
DOBSON AND CORNFORTH
Evaluation and Analysis Color was measured with a Hunter Lab Digital Color Difference Meter8 standardized with a cream-colored plate Number C-2785 (L = 78.2, a = 2.3, b = 21.5). A DZA low-voltage (9.75 V) halogen cycle lamp was used. The sample port size was 5.1 cm. For "L" or lightness values, 100 = absolute white and 0 = absolute black. Positive "a" values indicated red color intensity, whereas negative "a" values
indicated green color intensity. Similarly, yellow or blue colors were measured by positive or negative "b" values, respectively. Rolls were held at 3 C for 4 days before slicing. Slices were approximately 1.2 cm thick and 10 cm in diameter. Slices were placed on a thin glass plate immediately after slicing, and "L", "a", and "b" values were obtained within 10 s, or at 1 h after slicing, to evaluate fading. Readings (1 per slice) were taken on two separate slices per roll. Cooked meat pH was measured after blending a 10-g sample with 90 mL deionized water for 1 min with a Polytron homogenizer.9 The pH of filtered homogenate was measured with a Fisher Model 610A pH meter.10 Total extractable myoglobin (including myoglobin, oxymyoglobin, and metmyoglobin) was determined using a modification of the procedure of Warriss (1979). Five-gram samples in polyethylene centrifuge tubes were blended with a Polytron homogenizer for 30 s in 25 mL of ice cold .04 M phosphate buffer, pH 6.8. After pigment extraction for 1 h at 4 C, the homogenates were centrifuged at 6,500 x g for 45 min, and supernatant was further clarified by filtration through Whatman Number 1 filter paper.10 Visible absorbance spectra were obtained on a recording spectrophotometer.11 Absorbance values at 525,572, and 700 nm were used to calculate total undenatured myoglobin and percentage metmyoglobin of total myoglobin (Trout, 1989). Fat content of cooked rolls was determined by standard procedures, using petroleum ether as the solvent (Association of Official Analytical Chemists, 1984).
The experiment had a 3 x 2 factorial arrangement of treatments, with three methods of meat preparation (E, PE, and 4 Hely-Joly bowl chopper, Meat Packers and Butch- CG) and two milk proteins added (NFDM and WPC). The C rolls were prepared for E ers Supply, Los Angeles, CA 90001. 5 Koch Supplies, Inc., Kansas City, MO 64101. and CG preparations, resulting in a total of 6 Cryovac Division, W. R. Grace, Simpsonville, SC eight treatments. Three separate experi29681. ments were conducted (three separate forTModel TR2-17000, Vortron, Inc., Beloit, WI53511. mulations per treatment), using different 8 Model D25D2A, Hunter Associates Laboratory, boxes of meat from the same supplier. Inc., Reston, VA 22090. 9 Brinkmann Instruments, Westbury, NY 11590. Duplicate measurements for each replicate 10 Fisher Scientific Products, Salt Lake City, UT resulted in six individual measurements 84101. per treatment for color, pH, percentage fat, "Shimadzu Scientific Instruments, Columbia, MD and myoglobin pigment content of cooked 21046.
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 27, 2015
The E rolls were made by chopping meat4 with salt for 1.5 min. The ice and dry milk proteins were added and the mixture was chopped for 1 min. The fat was then added and chopping was continued for 2 min. The PE rolls were made by first chopping dry milk protein, fat, and one-half of the ice in the bowl chopper to form a paste-like fatprotein pre-emulsion, as described by van den Hoven (1987). The meat, salt, and the rest of the ice were then added and chopped for 2 min, for a total chopping time of about 5 min. The CG rolls were made by mixing meat thoroughly with other ingredients, and passing the mixture twice through a HobarP grinder with a .63-cm plate. After chopping or grinding, products were stuffed with a manual stuffer5 into 10-cm diameter, water-impermeable casings.6 The rolls were then laid on screens in the smokehouse7 and cooked (about 8 h) to an internal temperature of 74 C, with the smokehouse temperature set at 82 C, dampers closed, and relative humidity set at 100%. After cooking, rolls were stored at 2 C.
1945
NONFAT DRY MILK INHIBITS PINK DISCOLORATION TABLE 1. Mean Hunter "L" (lightness), "a" (redness), and "b" (yellowness) values of turkey rolls 10 s after slicing Sample 1 E-C E-NFDM E-WPC PE-NFDM PE-WPC CG-C CG-NFDM CG-WPC
"b" 65.7<» 65.9a 65.4^ 64.8o 64.4ob 65.0o 63.2b
63.2b
2.6b .9C 3.3o 1.0C 3.2o 3.4o l.lc 3.2a
11.7d 12.6a
11.8"1 12.3ob 12.0b<:d 10.9' 12.1b-: 11.2«
samples. Treatment groups were compared by one-way ANOVA (Anonymous, 1986) using the StatView™ 512+12 statistical package on a Macintosh SE computer.13 Means were separated by the least significant difference method. RESULTS AND DISCUSSION Cooked turkey rolls had a mean pH of 6.1 (range 6.09 to 6.16), a mean fat content of 6.79% (range 6.30 to 7.18%), and there were no differences among treatments. Compared with other treatments, lightness values were lower (P < .05) for CG rolls formulated with milk proteins (Table 1), in part because CG rolls had particles of thigh meat still visible. Mean lightness values for E, PE, and CG rolls were 65.7, 64.6, and 63.8, respectively [least significant difference at 5% level (LSD.05) = .8]. Nonfat dry milk lowered the redness values of turkey rolls. Control rolls made without milk proteins and rolls made with 3% WPC were noticeably pink upon slicing, and had "a" values ranging from 12 13
BrainPower, Inc., Calabasas, CA 91302. Apple Computer, Inc., Cupertino, CA 95014.
TABLE 2. Mean Hunter "L" (lightness), "a" (redness) and "b" (yellowness) values of turkey rolls 1 h after slicing
Sample1
"L"
"a"
"b"
E-C E-NFDM E-WPC PE-NFDM PE-WPC CG-C CG-NFDM CG-WPC
66.10 65.2b 65.3b 63.1d 64.4c 64.3C 61.9e 61.7^
.8b .3b l.iob .7b .8b l.iob .6b 1.70
12.8ob 12.90 13.00 12.7ob 13.00 12.4bc 12.1« 12.2'
o-*Values in columns with no common superscripts differ significantly (P < .05). For "L", "a", and "b", least significant difference values were .75, .81, and .45, respectively. For each treatment, n = 6. iE, PE, and CG refer to method of meat processing. E = emulsion, meat, fat, and other ingredients were finely chopped together; PE = preemulsion, fat, milk proteins and water were chopped to form a pre-emulsion, then chopped with meat; CG = coarse ground, meat and fat were passed through a .63-cm grinder plate, then mixed with other ingredients; C = control, no added milk protein; NFDM = nonfat dry milk; and WPC = whey protein concentrate.
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 27, 2015
o-tyalues in the same column with no common superscripts differ significantly (P < .05). For "L", "a", and "b", least significant difference values were 1.44, .48, and .34, respectively. For each treatment, n = 6. iE, PE, and CG refer to method of meat processing. E = emulsion, meat, fat, and other ingredients were finely chopped together; PE = preemulsion, fat, milk proteins, and water were chopped to form a pre-emulsion, then chopped with meat; CG = coarse ground, meat and fat were passed through a .63-cm grinder plate, then mixed with other ingredients; C = control, no added milk protein; NFDM = nonfat dry milk; and WPC = whey protein concentrate.
2.6 to 3.4. Slices from rolls formulated with 3% NFDM had no visible pink discoloration, and had significantly lower "a" values, ranging from .9 to 1.1. These results indicate that use of NFDM was effective in avoiding the pink discoloration that developed during refrigerated storage of turkey rolls. Pink discoloration faded quickly in C rolls or rolls made with WPC. By 1 h after slicing, all samples had a faded gray appearance, with "a" values ranging from .3 to 1.7 (Table 2). Pooled means for "a" values of samples formulated with WPC or NFDM were 3.25 and 1.02, respectively, immediately after slicing, compared with significantly lower values of 1.14 and .55, respectively, at 1 h after slicing (LSD.05 = »34). There was little relation of "b" (yellowness) values to pink discoloration of turkey rolls. Total undenatured myoglobin levels after cooking were higher in some rolls made with milk proteins, than in controls (Table 3). Trout (1989) also found that measurable levels of undenatured myoglobin remained in cooked turkey products, depending upon cooking temperature and meat pH. There is no readily apparent explanation for the observation that myoglobin denaturation was lower in
1946
DOBSON AND CORNFORTH
TABLE 3. Mean values for undenatured myoglobin and metmyoglobin in cooked turkey rolls
63-cm grinder plate, then mixed with other ingredients; C = control, no added milk protein; NFDM = nonfat dry milk; and WPC = whey protein concentrate. 2 Total myoglobin extracted in cold .04 M phosphate buffer, pH 6.8, including myoglobin, oxymyoglobin, and metmyoglobin. 3 Metmyoglobin as percentage of total myoglobin.
samples containing milk proteins. Percentage metmyoglobin values were not affected by milk proteins, but were lower in CG samples, probably because less oxygen was incorporated during grinding of CG samples, compared with chopping of emulsified samples. The mechanism by which NFDM inhibited pink discoloration is not known. Oxidation-reduction reactive sulfhydryls or other protein side-chains of NFDM may have raised the oxidation-reduction potential of the meat system, thus preventing formation of the complex between denatured proteins and heme. Nonfat dry milk may have decreased muscle protein denaturation during cooking, also inhibiting hemochrome formation. Alternatively, casein micelles in NFDM may simply mask the meat pigments. However, Ron-
REFERENCES Ann, D. U., and A. J. Maurer, 1990. Poultry meat color: Kinds of heme pigments and concentrations of the ligands. Poultry Sci. 69:157-165. Anonymous, 1986. Statview™ 512+. Brainpower, Inc., Calabasas, CA. Association of Official Analytical Chemists, 1984. Procedure 24.005, crude fat in meats. Page 431 in: Official Methods of Analysis, 14th ed., 1984. Association of Official Analytical Chemists, Washington, DC. Brown, W. D., and A. L. Tappel, 1957. Identification of the pink pigment of canned tuna. Food Res. 22:214-221. Comforth, D. P., F. Vahabzadeh, C. E. Carpenter, and D. T. Bartholomew, 1986. Role of reduced hemochromes in pink color defect of cooked turkey rolls. J. Food Sci. 51:1132-1135. Rongey, E. H., and L. J. Bratzler, 1966. The effect of various binders and meats on the palatability and processing characteristics of bologna. Food Technol. 20(9):1228-1231. Trout, G. R., 1989. Variation in myoglobin denaturation and color of cooked beef, pork, and turkey meat as influenced by pH, sodium chloride, sodium tripolyphosphate and cooking temperature. J. Food Sci. 54:536-544. van den Hoven, M., 1987. Functionality of dairy ingredients in meat products. Food Technol. 41(10):72-77. Warriss, P. D., 1979. The extraction of haem pigments from fresh meat. J. Food Technol. 14:75-80.
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 27, 2015
gey and Bratzler (1966) found that 10 to 20% NFDM was required to lighten bologna significantly, whereas in the current 1 2 3 study, rolls containing 3% NFDM were Sample Myoglobin Metmyoglobin not lighter than other samples. Another (mg/g of meat) (%) factor considered in the present study was E-C .36' 78.8ab that pre-emulsification of milk proteins b E-NFDM .64"bc 74.6 with fat may produce smaller, more E-WPC .66ab 80.1a PE-NFDM .46bc 85.4a refractive fat particles and a lighter PE-WPC .71* 77.1ab product. However, lightness values were CG-C .441* 58.51* not increased in pre-emulsified samples, a bc CG-NFDM .78 69.3 compared with similar samples prepared CG-WPC -71ab 69^ by chopping all ingredients together, "-'Values in the same column with no common superscripts differ significantly (P < .05). For my- without pre-emulsification. oglobin and percentage metmyoglobin, least signifiIn conclusion, a pink discoloration decant difference values were .285 and 10.5, respecveloped during refrigerated storage of C tively. For each treatment, n = 6. turkey rolls, or rolls formulated with *E, PE, and CG refer to method of meat processing. E = emulsion, meat, fat, and other WPC, but discoloration did not develop in ingredients were finely chopped together; PE = pre- rolls formulated with 3% NFDM. Thus, emulsion, fat, milk proteins and water were chopped NFDM may have application in prevento form a pre-emulsion, then chopped with meat; CG = coarse ground, meat and fat were passed through a tion of this common problem.
1992 Poultry Science 71:1943-1946
INTRODUCTION A pink discoloration is frequently observed on cut surfaces of cooked turkey rolls, and it is often interpreted by consumers as an indication of undercooking. Nitrite contamination of meat or ingredients is seldom the source of the problem. Hemochromes have been associated with pink color of turkey rolls (Cornforth et al, 1986) and canned tuna (Brown and Tappel, 1957). Hemochromes may develop under anaerobic conditions from the reaction of reduced heme and various nitrogenous groups, including amino side chains of denatured proteins (Cornforth et al., 1986; Ann and Maurer, 1990). Potassium iodate, an oxidizing agent, inhibits pink discoloration in cooked turkey meat (Cornforth et al, 1986), but is not acceptable for commercial use. Milk proteins, especially calcium caseinate, have been promoted for their
Received for publication March 31, 1992. Accepted for publication July 1, 1992. ^Authors appreciate the support of the Western Dairy Foods Research Center for this study. Journal Paper Number 4298 of the Utah Agricultural Experiment Station. 2 Present address: Golden Cheese Co. of California, 1138 West Rincon Street, Corona, CA 91720. 3 To whom correspondence should be addressed.
whitening effect in chicken nuggets formulated with thigh meat or mechanically deboned chicken (van den Hoven, 1987). Nonfat dried milk (NFDM) has been reported to lighten the color of bologna (Rongey and Bratzler, 1966). Milk proteins may also alleviate pink discoloration in poultry. The present study determined whether two dried milk protein products, NFDM and whey protein concentrate (WPC), affected the incidence of pink discoloration in turkey rolls. MATERIALS AND METHODS Formulation and Processing Turkey rolls (2.8 kg per treatment) were formulated to contain breast meat (90%), thigh meat (10%), water and ice (10%), internal or cluster fat (10%), salt (1%), and NFDM or WPC (3%), expressed as percentage of total meat weight (breast and thigh meat = 2.3 kg per treatment). Control (C) rolls were formulated without milk proteins. Frozen meat obtained from a regional processor was tempered overnight, then passed through a 2.5-cm plate before further processing. The possible effects of particle size and fat emulsification on color were evaluated by making turkey rolls from finely chopped meat emulsions (E), finely chopped meat and pre-emulsified fat (PE), or from coarsely ground meat (CG).
1943
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 27, 2015
ABSTRACT Pink discoloration in turkey rolls was prevented by incorporating 3% nonfat dry milk (NFDM) in the formulation. Coarsely ground, cooked turkey rolls formulated with NFDM also had higher levels of undenatured myoglobin than did controls. Nonfat dry milk may inhibit formation of reduced heme-denatured globin pigments (globin hemochromes) in cooked meat by inhibiting myoglobin denaturation or promoting heme oxidation. The mechanism of inhibition of pink discoloration by NFDM remains to be determined. (Key words: turkey, meat, color, myoglobin, nonfat dry milk)
1944
DOBSON AND CORNFORTH
Evaluation and Analysis Color was measured with a Hunter Lab Digital Color Difference Meter8 standardized with a cream-colored plate Number C-2785 (L = 78.2, a = 2.3, b = 21.5). A DZA low-voltage (9.75 V) halogen cycle lamp was used. The sample port size was 5.1 cm. For "L" or lightness values, 100 = absolute white and 0 = absolute black. Positive "a" values indicated red color intensity, whereas negative "a" values
indicated green color intensity. Similarly, yellow or blue colors were measured by positive or negative "b" values, respectively. Rolls were held at 3 C for 4 days before slicing. Slices were approximately 1.2 cm thick and 10 cm in diameter. Slices were placed on a thin glass plate immediately after slicing, and "L", "a", and "b" values were obtained within 10 s, or at 1 h after slicing, to evaluate fading. Readings (1 per slice) were taken on two separate slices per roll. Cooked meat pH was measured after blending a 10-g sample with 90 mL deionized water for 1 min with a Polytron homogenizer.9 The pH of filtered homogenate was measured with a Fisher Model 610A pH meter.10 Total extractable myoglobin (including myoglobin, oxymyoglobin, and metmyoglobin) was determined using a modification of the procedure of Warriss (1979). Five-gram samples in polyethylene centrifuge tubes were blended with a Polytron homogenizer for 30 s in 25 mL of ice cold .04 M phosphate buffer, pH 6.8. After pigment extraction for 1 h at 4 C, the homogenates were centrifuged at 6,500 x g for 45 min, and supernatant was further clarified by filtration through Whatman Number 1 filter paper.10 Visible absorbance spectra were obtained on a recording spectrophotometer.11 Absorbance values at 525,572, and 700 nm were used to calculate total undenatured myoglobin and percentage metmyoglobin of total myoglobin (Trout, 1989). Fat content of cooked rolls was determined by standard procedures, using petroleum ether as the solvent (Association of Official Analytical Chemists, 1984).
The experiment had a 3 x 2 factorial arrangement of treatments, with three methods of meat preparation (E, PE, and 4 Hely-Joly bowl chopper, Meat Packers and Butch- CG) and two milk proteins added (NFDM and WPC). The C rolls were prepared for E ers Supply, Los Angeles, CA 90001. 5 Koch Supplies, Inc., Kansas City, MO 64101. and CG preparations, resulting in a total of 6 Cryovac Division, W. R. Grace, Simpsonville, SC eight treatments. Three separate experi29681. ments were conducted (three separate forTModel TR2-17000, Vortron, Inc., Beloit, WI53511. mulations per treatment), using different 8 Model D25D2A, Hunter Associates Laboratory, boxes of meat from the same supplier. Inc., Reston, VA 22090. 9 Brinkmann Instruments, Westbury, NY 11590. Duplicate measurements for each replicate 10 Fisher Scientific Products, Salt Lake City, UT resulted in six individual measurements 84101. per treatment for color, pH, percentage fat, "Shimadzu Scientific Instruments, Columbia, MD and myoglobin pigment content of cooked 21046.
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 27, 2015
The E rolls were made by chopping meat4 with salt for 1.5 min. The ice and dry milk proteins were added and the mixture was chopped for 1 min. The fat was then added and chopping was continued for 2 min. The PE rolls were made by first chopping dry milk protein, fat, and one-half of the ice in the bowl chopper to form a paste-like fatprotein pre-emulsion, as described by van den Hoven (1987). The meat, salt, and the rest of the ice were then added and chopped for 2 min, for a total chopping time of about 5 min. The CG rolls were made by mixing meat thoroughly with other ingredients, and passing the mixture twice through a HobarP grinder with a .63-cm plate. After chopping or grinding, products were stuffed with a manual stuffer5 into 10-cm diameter, water-impermeable casings.6 The rolls were then laid on screens in the smokehouse7 and cooked (about 8 h) to an internal temperature of 74 C, with the smokehouse temperature set at 82 C, dampers closed, and relative humidity set at 100%. After cooking, rolls were stored at 2 C.
1945
NONFAT DRY MILK INHIBITS PINK DISCOLORATION TABLE 1. Mean Hunter "L" (lightness), "a" (redness), and "b" (yellowness) values of turkey rolls 10 s after slicing Sample 1 E-C E-NFDM E-WPC PE-NFDM PE-WPC CG-C CG-NFDM CG-WPC
"b" 65.7<» 65.9a 65.4^ 64.8o 64.4ob 65.0o 63.2b
63.2b
2.6b .9C 3.3o 1.0C 3.2o 3.4o l.lc 3.2a
11.7d 12.6a
11.8"1 12.3ob 12.0b<:d 10.9' 12.1b-: 11.2«
samples. Treatment groups were compared by one-way ANOVA (Anonymous, 1986) using the StatView™ 512+12 statistical package on a Macintosh SE computer.13 Means were separated by the least significant difference method. RESULTS AND DISCUSSION Cooked turkey rolls had a mean pH of 6.1 (range 6.09 to 6.16), a mean fat content of 6.79% (range 6.30 to 7.18%), and there were no differences among treatments. Compared with other treatments, lightness values were lower (P < .05) for CG rolls formulated with milk proteins (Table 1), in part because CG rolls had particles of thigh meat still visible. Mean lightness values for E, PE, and CG rolls were 65.7, 64.6, and 63.8, respectively [least significant difference at 5% level (LSD.05) = .8]. Nonfat dry milk lowered the redness values of turkey rolls. Control rolls made without milk proteins and rolls made with 3% WPC were noticeably pink upon slicing, and had "a" values ranging from 12 13
BrainPower, Inc., Calabasas, CA 91302. Apple Computer, Inc., Cupertino, CA 95014.
TABLE 2. Mean Hunter "L" (lightness), "a" (redness) and "b" (yellowness) values of turkey rolls 1 h after slicing
Sample1
"L"
"a"
"b"
E-C E-NFDM E-WPC PE-NFDM PE-WPC CG-C CG-NFDM CG-WPC
66.10 65.2b 65.3b 63.1d 64.4c 64.3C 61.9e 61.7^
.8b .3b l.iob .7b .8b l.iob .6b 1.70
12.8ob 12.90 13.00 12.7ob 13.00 12.4bc 12.1« 12.2'
o-*Values in columns with no common superscripts differ significantly (P < .05). For "L", "a", and "b", least significant difference values were .75, .81, and .45, respectively. For each treatment, n = 6. iE, PE, and CG refer to method of meat processing. E = emulsion, meat, fat, and other ingredients were finely chopped together; PE = preemulsion, fat, milk proteins and water were chopped to form a pre-emulsion, then chopped with meat; CG = coarse ground, meat and fat were passed through a .63-cm grinder plate, then mixed with other ingredients; C = control, no added milk protein; NFDM = nonfat dry milk; and WPC = whey protein concentrate.
Downloaded from http://ps.oxfordjournals.org/ at University of Bath, Library on June 27, 2015
o-tyalues in the same column with no common superscripts differ significantly (P < .05). For "L", "a", and "b", least significant difference values were 1.44, .48, and .34, respectively. For each treatment, n = 6. iE, PE, and CG refer to method of meat processing. E = emulsion, meat, fat, and other ingredients were finely chopped together; PE = preemulsion, fat, milk proteins, and water were chopped to form a pre-emulsion, then chopped with meat; CG = coarse ground, meat and fat were passed through a .63-cm grinder plate, then mixed with other ingredients; C = control, no added milk protein; NFDM = nonfat dry milk; and WPC = whey protein concentrate.
2.6 to 3.4. Slices from rolls formulated with 3% NFDM had no visible pink discoloration, and had significantly lower "a" values, ranging from .9 to 1.1. These results indicate that use of NFDM was effective in avoiding the pink discoloration that developed during refrigerated storage of turkey rolls. Pink discoloration faded quickly in C rolls or rolls made with WPC. By 1 h after slicing, all samples had a faded gray appearance, with "a" values ranging from .3 to 1.7 (Table 2). Pooled means for "a" values of samples formulated with WPC or NFDM were 3.25 and 1.02, respectively, immediately after slicing, compared with significantly lower values of 1.14 and .55, respectively, at 1 h after slicing (LSD.05 = »34). There was little relation of "b" (yellowness) values to pink discoloration of turkey rolls. Total undenatured myoglobin levels after cooking were higher in some rolls made with milk proteins, than in controls (Table 3). Trout (1989) also found that measurable levels of undenatured myoglobin remained in cooked turkey products, depending upon cooking temperature and meat pH. There is no readily apparent explanation for the observation that myoglobin denaturation was lower in
1946
DOBSON AND CORNFORTH
TABLE 3. Mean values for undenatured myoglobin and metmyoglobin in cooked turkey rolls
63-cm grinder plate, then mixed with other ingredients; C = control, no added milk protein; NFDM = nonfat dry milk; and WPC = whey protein concentrate. 2 Total myoglobin extracted in cold .04 M phosphate buffer, pH 6.8, including myoglobin, oxymyoglobin, and metmyoglobin. 3 Metmyoglobin as percentage of total myoglobin.
samples containing milk proteins. Percentage metmyoglobin values were not affected by milk proteins, but were lower in CG samples, probably because less oxygen was incorporated during grinding of CG samples, compared with chopping of emulsified samples. The mechanism by which NFDM inhibited pink discoloration is not known. Oxidation-reduction reactive sulfhydryls or other protein side-chains of NFDM may have raised the oxidation-reduction potential of the meat system, thus preventing formation of the complex between denatured proteins and heme. Nonfat dry milk may have decreased muscle protein denaturation during cooking, also inhibiting hemochrome formation. Alternatively, casein micelles in NFDM may simply mask the meat pigments. However, Ron-
REFERENCES Ann, D. U., and A. J. Maurer, 1990. Poultry meat color: Kinds of heme pigments and concentrations of the ligands. Poultry Sci. 69:157-165. Anonymous, 1986. Statview™ 512+. Brainpower, Inc., Calabasas, CA. Association of Official Analytical Chemists, 1984. Procedure 24.005, crude fat in meats. Page 431 in: Official Methods of Analysis, 14th ed., 1984. Association of Official Analytical Chemists, Washington, DC. Brown, W. D., and A. L. Tappel, 1957. Identification of the pink pigment of canned tuna. Food Res. 22:214-221. Comforth, D. P., F. Vahabzadeh, C. E. Carpenter, and D. T. Bartholomew, 1986. Role of reduced hemochromes in pink color defect of cooked turkey rolls. J. Food Sci. 51:1132-1135. Rongey, E. H., and L. J. Bratzler, 1966. The effect of various binders and meats on the palatability and processing characteristics of bologna. Food Technol. 20(9):1228-1231. Trout, G. R., 1989. Variation in myoglobin denaturation and color of cooked beef, pork, and turkey meat as influenced by pH, sodium chloride, sodium tripolyphosphate and cooking temperature. J. Food Sci. 54:536-544. van den Hoven, M., 1987. Functionality of dairy ingredients in meat products. Food Technol. 41(10):72-77. Warriss, P. D., 1979. The extraction of haem pigments from fresh meat. J. Food Technol. 14:75-80.
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gey and Bratzler (1966) found that 10 to 20% NFDM was required to lighten bologna significantly, whereas in the current 1 2 3 study, rolls containing 3% NFDM were Sample Myoglobin Metmyoglobin not lighter than other samples. Another (mg/g of meat) (%) factor considered in the present study was E-C .36' 78.8ab that pre-emulsification of milk proteins b E-NFDM .64"bc 74.6 with fat may produce smaller, more E-WPC .66ab 80.1a PE-NFDM .46bc 85.4a refractive fat particles and a lighter PE-WPC .71* 77.1ab product. However, lightness values were CG-C .441* 58.51* not increased in pre-emulsified samples, a bc CG-NFDM .78 69.3 compared with similar samples prepared CG-WPC -71ab 69^ by chopping all ingredients together, "-'Values in the same column with no common superscripts differ significantly (P < .05). For my- without pre-emulsification. oglobin and percentage metmyoglobin, least signifiIn conclusion, a pink discoloration decant difference values were .285 and 10.5, respecveloped during refrigerated storage of C tively. For each treatment, n = 6. turkey rolls, or rolls formulated with *E, PE, and CG refer to method of meat processing. E = emulsion, meat, fat, and other WPC, but discoloration did not develop in ingredients were finely chopped together; PE = pre- rolls formulated with 3% NFDM. Thus, emulsion, fat, milk proteins and water were chopped NFDM may have application in prevento form a pre-emulsion, then chopped with meat; CG = coarse ground, meat and fat were passed through a tion of this common problem.