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Biochemical and Color Characteristics of Skinless Boneless Pale Chicken Breast
Biochemical and Color Characteristics of Skinless Boneless Pale Chicken Breast M. BOULIANNE Dtpartement de Sciences Cliniaues, Faculti de Midecine Vetirinaire, Universiti de Montrial, C.P. 5000, St-Hyacinthe, Quibec, Canada, J2S 7C6 A. J. KING Department of Avian Sciences, University of California, Davis, California 95616
1995 Poultry Science 74:1693-1698
some incidences of pale processed poultry breast meat have been reported, van Hoof Color of processed poultry muscle is of (1979) and Barbut (1993) suggested that concern to processors, retailers, and con- poultry breast muscle can exhibit the same sumers and can be a reason for rejection pale soft exudative (PSE) characteristics as during production and prior to consump- seen in pork. tion. Froning and Hartung (1967), Froning Recently, pale color of chicken breast et al. (1968), Ngoka et al. (1982), and Ahn meat was observed postchilling at a local and Maurer (1990) have reviewed prob- processing plant and at the retail stores. lems related to red or pink color in The pale processed meat was described by processed, uncooked, and cooked poultry the company as light white-yellow dismeat. Although red or pink color prob- colored breast meat turning to a pale gray lems have been discussed most often, discoloration during storing and distribution, with no evidence of excessive microbial growth. In cooperation with the local processing plant, a study was underReceived for publication November 7, 1994. taken to determine factors associated with Accepted for publication June 5, 1995. INTRODUCTION
1693
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
ABSTRACT Extreme paleness of skinless, boneless chicken breasts sampled from the packaging area of a commercial processing plant was investigated. Six hundred fillets were collected during 10 visits to the same processing plant and were classified as normal (n = 300) and pale (n = 300) according to visual assessment by the principal investigator. Color (spectrocolorimetry) and pH of each fillet were measured within 1 h following collection. Fillets were frozen in liquid nitrogen and pooled samples of pale and normal meat were later analyzed for thiobarbituric acid reactive substances (TBARS), percentage moisture, total pigment, myoglobin, and iron concentrations. Color characteristics (L, a, and b values), pH, total pigment, myoglobin, and iron concentrations were all found to be significantly different in pale meat when compared with normal chicken breast. The TBARS values and percentage moisture for the two groups were not different. Analyses of L, a, and b values revealed that the L characteristic was a good color indicator that can be used to distinguish normal from pale samples, with both high sensitivity and high specificity. Moisture uptake in postchilled, pale fillets could not account for the decrease in total pigment concentration and myoglobin content. (Key words: chicken, meat color, myoglobin, pigment content, moisture)
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BOULIANNE ET AL.
Color and pH
Model DLC7, Cuisinart, Greenwich, CT 06830. horning pH meter 240, Corning Science Products, Coming, NY 14831. sColormet, Instrumar Ltd., St. John's, NF, Canada A1B 4A5.
Iron Measurement
Color and pH were determined within 1 h following collection. Measurements were taken on the outer ventral surface, in the middle of the cranial third of the P. major, with a pH meter2 (direct probe method) in a MATERIALS AND METHODS small incision, and a surface spectrocolorimeterS using the Standard CIELAB Sample Collection Color System (L = lightness; a = redness, Skinless, boneless broiler chicken Pec- and b = yellowness). The spectrocolorimeter tordlis major muscles were collected in the was standardized every 30 measurements packaging area, after skinning, during 10 against a reference white tile (L = 94.5 ± .2, a visits to a local processing plant. These P. = -1.0 ± .1, b = .0 ± .2). major muscles were deboned breast fillets from chilled carcasses. These deboned fillets had been placed in containers lined Thiobarblturic Acid Reactive with plastic bags covered with ice at 4 C for Substances a minimum of 24 h and up to 72 h after Thiobarbituric acid reactive substances slaughter, before packaging. Three hun(TBARS) were measured on the day followdred normal and 300 pale breasts were ing sampling with the modified thiobarbisampled on a conveyor belt, before packagturic acid assay of Salih et dl. (1987). Six ing, based on visual assessment by the same replicates were analyzed from each pool of investigator, and according to the company description of pale and normal. All sampled chicken breast samples. breasts were uniform in coloration with no sign of overscalding. Chicken breasts were immediately placed on ice after collection Percentage Moisture with the ventral side up for a maximum of 1 Percentage moisture was measured on h, until color and pH measurements were the day following sampling and according made. The cranial third of the breast was then cut and frozen in liquid nitrogen. Cut to the Association of Official Analytical frozen samples were bagged and stored in Chemists (1990), with the exception that the ice during transport to the laboratory. Upon laboratory vacuum-oven temperature was arrival at the laboratory, samples were set at 65 C. pooled according to their respective color group and ground at 4 C in a food processor1 by method of King and Bosch Total Pigment Concentration and (1990), in particle size of approximately 2 Myoglobin Content mm of diameter. Pooling was judged to be Two 10-g replicates from each pool were necessary because testing of each in- collected. Total pigment and myoglobin dividual sample was impractical. Ten-gram content were measured using a technique portions of the ground meat were weighed, wrapped in plastic film, stored overnight at after Rickansrud and Henrickson (1967). 4 C for malonaldehyde determination and Initial pigment extraction was done with 25 moisture content, or kept frozen at -20 C mL of ice-cold .04 M phosphate buffer, pH until measurement of total pigment, my- 6.8 (Warriss, 1979). A chicken myoglobin molecular weight of 18,026 g/mol was used oglobin, and iron concentrations. for calculations. Myoglobin content was measured only for the first five plant visits.
Two replicates from each pool, for the 10 visits, were analyzed for iron. Meat samples
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
paleness in boneless, skinless chicken breast fillets and to determine a test or a color variable offering an accurate measurement of paleness for future classification purposes.
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PALENESS OF CHICKEN BREAST MEAT
TABLE 1. Pigment contents, percentage moisture, thiobarbituric acid reactive substances (TBARS), and pH of skinless boneless pale and normal chicken breast meat (3J ± SD) Biochemical and physical characteristics1
Pale breast
Normal breast
Total pigment concentration, mg/g Myoglobin content, mg/g Iron, ppm Moisture, % TBARS pH L a b
.96 .12 16.6 76.05 .115 5.86 59.2 1.7 10.1
1.47 .17 19.7 75.4 .095 5.68 52.3 3.2 8.4
± ± ± ± ± ± ± ± ±
.22» .03b 1.0B 1.26 .204 .10* 2.2* .8B 1.9*
± ± ± ± ± ± ± ± ±
.27* .07» 3.0* .89 .205 .11B 2.8B 1.2* 2.1B
- Means in the same row with no common superscript differ significantly (P £ .05). ' Means in the same row with no common superscript differ significantly (P £ .01). l n = 10 for all means excluding total pigment concentration and iron, where n = 20; and pH, L, a, and b, where n 300. AB
were dried in oven at 40 C for 2 h and iron measurement was determined by inductively coupled plasma spectrometry (Matusiewicv et al, 1989) at the Division of Agriculture and Natural Resources Diagnostic Laboratory at the University of California, Davis. Results are reported on a dry weight basis.
lation coefficients were computed to assess the linear relationship between averaged color characteristic values (L, a, or b) and total pigment concentration, myoglobin content, iron content, and percentage moisture. Sensitivity (proportion of pale samples so identified) and specificity (proportion of normal samples so identified) were calculated for the L, a, and b values. Because color Statistical Analysis of the meat by spectrocolorimeter is measured on a continuous scale, each one-unit A total of 600 chicken breast samples or change across the range of sampled values units were collected during 10 visits to a plant. These 600 independent units were of L, a, or b were respectively considered as divided in two color groups based on the cut-points. For all cut-points and the L, a, criteria previously described. Color and pH and b values of the color system considered, were measured on all units. Percentage cross-classification of the visual evaluation moisture, TBARS, total pigment concentra- and the test result was performed, and the sensitivity and the specificity of the test was tion, myoglobin, and iron contents were calculated. Statistical analyses were permeasured from pooled samples. A pooled formed using the STATISTIX 4.0* and SAS® sample consisted of 30 breasts or units computer programs.5 pooled in each color group, with one pooled sample per color group per visit. Two RESULTS AND DISCUSSION sample t tests were used to determine whether the total pigment concentration, the myoglobin content, the iron content, Pigments and Moisture Contents and the percentage moisture were different One objective of the present study was to among two color groups; pale and normal determine the source of paleness in chicken chicken breasts. For each pooled sample, the corresponding color characteristic breast. There was no difference for the values were averaged, and Pearson's corre- TBARS and the percentage moisture between the two groups (Table 1). Total pigment, myoglobin, and iron concentrations were significantly lower in the pale 4 breast meat as compared with the normal Analytical Software, St. Paul, MN 55113. breast meat (Table 1). 5SAS Institute, Cary, NC 27513.
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
a b
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BOUUANNE ET AL.
TABLE 2. Pearson's correlation coefficients between color values and total pigment concentration, myoglobin, and iron contents for chicken breast meat Color values
Total pigment concentration
Myoglobin content
Iron content
L a b
-.81" .60" -.63"
-.52* .54* -.46*
-.52* .68" -.25
*P £ .05. **p <; .01.
tively. A similar correlation has been reported by Barbut (1993) and van Hoof (1979), who made measurements in light to dark turkey breast meat. These authors suggested that apparent pale color in poultry meat is associated with lower pH and is similar to the PSE condition in pork meat. The post-mortem physical environment of muscle was examined as a potential cause for meat paleness. Observations made in the processing plant revealed that deboned breast fillets from chilled carcasses were stored in boxes lined with plastic bags and filled with ice. These fillets were then held at 4 C in boxes for a minimum of 24 h, and up to 78 h before sampling. Moisture uptake and consequent "dilution" of pigments cannot explain difference in discoloration, as there was no difference in percentage moisture between the two groups. However, moisture uptake on the surface of the fillets was not tested, dilution of the pigments on the surface could be another probability. It is possible that prolonged contact with melt water favored release of meat pigments, therefore causing the meat to look paler. It was indeed observed that water present in the bottom of the boxes had a light pink color after storage. Sample collection was performed on a conveyor belt after storage in containers and before packaging, and thus was considered to be randomized. This study did not verify whether location of the meat in boxes, i.e., top or bottom, and time spent in storage affected meat paleness, but this warrants further investigation. Fleming et al. (1991) reported no difference in heme pigment levels between ice-slush-chilled and airchilled chicken carcasses. They, however, chilled the whole carcass before deboning
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
The reason for difference in pigment concentration between the two groups is unknown. Ante-mortem factors such as preslaughter excitement, heat stress, and free struggle have been reported to increase meat redness (Froning et al, 1978; Ngoka et al, 1982). Myoglobin has also been shown to vary with age and sex in turkeys, therefore affecting meat color (Froning et ah, 1968). As all broiler chickens were approximately the same age when processed, this factor cannot account for paleness of breast meat used in this study. It is, however, unknown whether sex played a role in predisposing chicken breast meat to paleness in this study. There was no correlation between TBARS values and heme pigment concentrations. It has been suggested that difference in concentrations of heme pigments from stored, raw muscles of three species affects TBARS values (Rhee and Ziprin, 1987). The variation in amounts of pigments in the two groups of muscle may not have been great enough to cause a difference in TBARS values. It is also possible that TBARS values and total pigment would have been more closely related in muscle stored for a longer period of time. There were significant negative correlations between L color value and total pigment, myoglobin, and iron concentrations (Table 2), indicating that the decrease in pigment concentrations increased meat lightness. The a color value was positively correlated with total pigment, myoglobin, and iron concentrations (Table 2). This finding seems reasonable, as the a value measures meat redness. There was a significant correlation between L value and pH of -.51 and -.44 (P < .01) for the pale and normal meat, respec-
1697
PALENESS OF CHICKEN BREAST MEAT
and analysis and did not test the effect of ice-slush storage on deboned chicken fillets. Total pigment values appear two to three times higher than those reported in the literature (Ngoka et ah, 1982; Fleming et al, 1991). The present authors cannot explain this difference, which was consistent over the study period. Normal breast myoglobin values were similar to that reported by Fleming et al. (1991) for ice-slush-chilled chicken breast.
1 2 3 4 5 a value (cut-points)
The second objective of this study was to develop an effective method that would objectively discriminate normal from pale chicken meat. Considering each parameter of the CIELAB Color System as a test, the sensitivity (Se) and specificity (Sp) of the L, a, and b characteristics were calculated for a set of cut-points (Figures 1 and 2). For a particular test, the cut-point associated with the optimum combination of Se and Sp gives the highest value. The test is usually interpreted as good if, at that cut-point, both Se and Sp are reasonably high. The choice of an appropriate cut-point remains, however, entirely dependent on the desire to maximize Se only, Sp only, or both of these test characteristics. When the maximum efficiency criterion is applied to the analysis of each color parameter, results indicated that the L color characteristic was
b value (cut-points) --Sensitivity
"O" Specificity
FIGURE 2. Sensitivity and specificity of a and b values when measuring color of normal and pale chicken breast meat. Sensitivity and specificity distribution of a and b values obtained from spectrocolorimetry. The prevalence of pale chicken breast meat is set to 50%.
relatively the best test to discriminate pale from normal meat (Figure 1), whereas the a and b characteristics presented much lower discriminant abilities (Figure 2). In our experimental setting, for example, if the L test were to be used at its maximum 5 -6 efficiency, the cut-point value for L could be set at 56.3 L units where Se and Sp are both £ •« 92%. However, if the Se of the L test is prioritized (minimizing the percentage of pale meat classified as normal), one appropriate cut-point could have been set to 0 52.8 L units, giving a Se of 100% and a Sp of 40 42 44 46 48 SO 52 54 56 58 60 62 64 66 68 70 L v a l u e (cut-points) 56%. Interestingly, these calculations show that the lightness of the meat, over its ^Sensitivity ^Specificity redness or its yellowness, is what the FIGURE 1. Sensitivity and specificity of L value human eye detects when judging a pale when measuring color of normal and pale chicken meat. breast meat. Sensitivity and specificity distribution of L The results suggest that the paleness of values obtained from spectrocolorimetry. The prevalence of pale chicken breast meat is set to 50%. boneless chicken breast stored in ice slush
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
Color Measurement
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BOULIANNE ET Ah.
might be due to leakage of heme pigments in water. Moisture content values of pale and normal meat were not different, and therefore moisture uptake could not account for the difference in total pigment, myoglobin, and iron concentrations. Analyses of L, a, and b values revealed that L values could be used with high sensitivity and high specificity when used to distinguish pale from normal samples.
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meat as affected by age, sex and strain. Poultry Sci. 47:1827-1835. Froning, G. W, and T. E. Hartung, 1967. Effect of age, sex and strain on color and texture of turkey meat. Poultry Sci. 46:1261. King, A. J., and N. Bosch, 1990. Effect of NaCl and KCl on rancidity of dark turkey meat heated by microwave. J. Food Sci. 55:1549-1551. Matusiewicv, H., R. E. Sturgeon, and S. S. Berman, 1989. Trace element analysis of biological material following pressure digestion with nitric acidhydrogen peroxide and microwave heating. J. Anal. At. Spectrom. 4:323-327. Ngoka, D. A., G. W. Froning, S. R. Lowry, and A. S. Babji, 1982. Effects of sex, age, preslaughter REFERENCES factors and holding conditions on the quality Ann, D. U., and A. J. Maurer, 1990. Poultry meat color: characteristics and chemical composition of turkinds of heme pigments and concentrations of the key breast muscles. Poultry Sci. 61:1996-2003. ligands. Poultry Sci. 69:157-165. Rhee, K. S., and Y. A. Ziprin, 1987. Lipid oxidation in Association of Official Analytical Chemists, 1990. retail beef, pork and chicken muscles as affected Official Methods of Analysis. 15th ed. Association by concentrations of heme pigments and nonof Official Analytical Chemists, Washington, DC. heme iron and microsomal enzymic lipid peroxiBarbut, S., 1993. Colour measurements for evaluating dation activity. J. Food. Biochem. 11:1-15. the pale soft exudative (PSE) occurrence in turkey Rickansrud, D. A., and R. L. Henrickson, 1967. Total meat. Food Res. Int. 26:39-43. pigments and myoglobin concentration in four Fleming, B. K., G. W. Froning, and T. S. Yang, 1991. bovine muscles. J. Food Sci. 32:57-61. Heme pigment levels in chicken broilers chilled in Salih, A. M., D. M. Smith, J. F. Price, and L. E. Dawson, ice slush and air. Poultry Sci. 70:2197-2200. 1987. Modified extraction 2-thiobarbituric acid Froning, G. W., A. S. Babji, and F. B. Mather, 1978. The method for measuring lipid oxidation in poultry. effect of preslaughter temperature, stress, strugPoultry Sci. 66:1483-1488. gle and anesthetization on color and textural van Hoof, J., 1979. Influence of ante- and peri-mortem characteristics of turkey muscle. Poultry Sci. 57: factors on biochemical and physical characteris630-633. tics of turkey breast muscle. Vet. Q. 1:29-36. Froning, G. W., J. Daddario, and T. E. Hartung, 1968. Warriss, P. D., 1979. The extraction of haem pigments Color and myoglobin concentration in turkey from fresh meat. J. Food Technol. 14:75-80.
1995 Poultry Science 74:1693-1698
some incidences of pale processed poultry breast meat have been reported, van Hoof Color of processed poultry muscle is of (1979) and Barbut (1993) suggested that concern to processors, retailers, and con- poultry breast muscle can exhibit the same sumers and can be a reason for rejection pale soft exudative (PSE) characteristics as during production and prior to consump- seen in pork. tion. Froning and Hartung (1967), Froning Recently, pale color of chicken breast et al. (1968), Ngoka et al. (1982), and Ahn meat was observed postchilling at a local and Maurer (1990) have reviewed prob- processing plant and at the retail stores. lems related to red or pink color in The pale processed meat was described by processed, uncooked, and cooked poultry the company as light white-yellow dismeat. Although red or pink color prob- colored breast meat turning to a pale gray lems have been discussed most often, discoloration during storing and distribution, with no evidence of excessive microbial growth. In cooperation with the local processing plant, a study was underReceived for publication November 7, 1994. taken to determine factors associated with Accepted for publication June 5, 1995. INTRODUCTION
1693
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
ABSTRACT Extreme paleness of skinless, boneless chicken breasts sampled from the packaging area of a commercial processing plant was investigated. Six hundred fillets were collected during 10 visits to the same processing plant and were classified as normal (n = 300) and pale (n = 300) according to visual assessment by the principal investigator. Color (spectrocolorimetry) and pH of each fillet were measured within 1 h following collection. Fillets were frozen in liquid nitrogen and pooled samples of pale and normal meat were later analyzed for thiobarbituric acid reactive substances (TBARS), percentage moisture, total pigment, myoglobin, and iron concentrations. Color characteristics (L, a, and b values), pH, total pigment, myoglobin, and iron concentrations were all found to be significantly different in pale meat when compared with normal chicken breast. The TBARS values and percentage moisture for the two groups were not different. Analyses of L, a, and b values revealed that the L characteristic was a good color indicator that can be used to distinguish normal from pale samples, with both high sensitivity and high specificity. Moisture uptake in postchilled, pale fillets could not account for the decrease in total pigment concentration and myoglobin content. (Key words: chicken, meat color, myoglobin, pigment content, moisture)
1694
BOULIANNE ET AL.
Color and pH
Model DLC7, Cuisinart, Greenwich, CT 06830. horning pH meter 240, Corning Science Products, Coming, NY 14831. sColormet, Instrumar Ltd., St. John's, NF, Canada A1B 4A5.
Iron Measurement
Color and pH were determined within 1 h following collection. Measurements were taken on the outer ventral surface, in the middle of the cranial third of the P. major, with a pH meter2 (direct probe method) in a MATERIALS AND METHODS small incision, and a surface spectrocolorimeterS using the Standard CIELAB Sample Collection Color System (L = lightness; a = redness, Skinless, boneless broiler chicken Pec- and b = yellowness). The spectrocolorimeter tordlis major muscles were collected in the was standardized every 30 measurements packaging area, after skinning, during 10 against a reference white tile (L = 94.5 ± .2, a visits to a local processing plant. These P. = -1.0 ± .1, b = .0 ± .2). major muscles were deboned breast fillets from chilled carcasses. These deboned fillets had been placed in containers lined Thiobarblturic Acid Reactive with plastic bags covered with ice at 4 C for Substances a minimum of 24 h and up to 72 h after Thiobarbituric acid reactive substances slaughter, before packaging. Three hun(TBARS) were measured on the day followdred normal and 300 pale breasts were ing sampling with the modified thiobarbisampled on a conveyor belt, before packagturic acid assay of Salih et dl. (1987). Six ing, based on visual assessment by the same replicates were analyzed from each pool of investigator, and according to the company description of pale and normal. All sampled chicken breast samples. breasts were uniform in coloration with no sign of overscalding. Chicken breasts were immediately placed on ice after collection Percentage Moisture with the ventral side up for a maximum of 1 Percentage moisture was measured on h, until color and pH measurements were the day following sampling and according made. The cranial third of the breast was then cut and frozen in liquid nitrogen. Cut to the Association of Official Analytical frozen samples were bagged and stored in Chemists (1990), with the exception that the ice during transport to the laboratory. Upon laboratory vacuum-oven temperature was arrival at the laboratory, samples were set at 65 C. pooled according to their respective color group and ground at 4 C in a food processor1 by method of King and Bosch Total Pigment Concentration and (1990), in particle size of approximately 2 Myoglobin Content mm of diameter. Pooling was judged to be Two 10-g replicates from each pool were necessary because testing of each in- collected. Total pigment and myoglobin dividual sample was impractical. Ten-gram content were measured using a technique portions of the ground meat were weighed, wrapped in plastic film, stored overnight at after Rickansrud and Henrickson (1967). 4 C for malonaldehyde determination and Initial pigment extraction was done with 25 moisture content, or kept frozen at -20 C mL of ice-cold .04 M phosphate buffer, pH until measurement of total pigment, my- 6.8 (Warriss, 1979). A chicken myoglobin molecular weight of 18,026 g/mol was used oglobin, and iron concentrations. for calculations. Myoglobin content was measured only for the first five plant visits.
Two replicates from each pool, for the 10 visits, were analyzed for iron. Meat samples
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
paleness in boneless, skinless chicken breast fillets and to determine a test or a color variable offering an accurate measurement of paleness for future classification purposes.
1695
PALENESS OF CHICKEN BREAST MEAT
TABLE 1. Pigment contents, percentage moisture, thiobarbituric acid reactive substances (TBARS), and pH of skinless boneless pale and normal chicken breast meat (3J ± SD) Biochemical and physical characteristics1
Pale breast
Normal breast
Total pigment concentration, mg/g Myoglobin content, mg/g Iron, ppm Moisture, % TBARS pH L a b
.96 .12 16.6 76.05 .115 5.86 59.2 1.7 10.1
1.47 .17 19.7 75.4 .095 5.68 52.3 3.2 8.4
± ± ± ± ± ± ± ± ±
.22» .03b 1.0B 1.26 .204 .10* 2.2* .8B 1.9*
± ± ± ± ± ± ± ± ±
.27* .07» 3.0* .89 .205 .11B 2.8B 1.2* 2.1B
- Means in the same row with no common superscript differ significantly (P £ .05). ' Means in the same row with no common superscript differ significantly (P £ .01). l n = 10 for all means excluding total pigment concentration and iron, where n = 20; and pH, L, a, and b, where n 300. AB
were dried in oven at 40 C for 2 h and iron measurement was determined by inductively coupled plasma spectrometry (Matusiewicv et al, 1989) at the Division of Agriculture and Natural Resources Diagnostic Laboratory at the University of California, Davis. Results are reported on a dry weight basis.
lation coefficients were computed to assess the linear relationship between averaged color characteristic values (L, a, or b) and total pigment concentration, myoglobin content, iron content, and percentage moisture. Sensitivity (proportion of pale samples so identified) and specificity (proportion of normal samples so identified) were calculated for the L, a, and b values. Because color Statistical Analysis of the meat by spectrocolorimeter is measured on a continuous scale, each one-unit A total of 600 chicken breast samples or change across the range of sampled values units were collected during 10 visits to a plant. These 600 independent units were of L, a, or b were respectively considered as divided in two color groups based on the cut-points. For all cut-points and the L, a, criteria previously described. Color and pH and b values of the color system considered, were measured on all units. Percentage cross-classification of the visual evaluation moisture, TBARS, total pigment concentra- and the test result was performed, and the sensitivity and the specificity of the test was tion, myoglobin, and iron contents were calculated. Statistical analyses were permeasured from pooled samples. A pooled formed using the STATISTIX 4.0* and SAS® sample consisted of 30 breasts or units computer programs.5 pooled in each color group, with one pooled sample per color group per visit. Two RESULTS AND DISCUSSION sample t tests were used to determine whether the total pigment concentration, the myoglobin content, the iron content, Pigments and Moisture Contents and the percentage moisture were different One objective of the present study was to among two color groups; pale and normal determine the source of paleness in chicken chicken breasts. For each pooled sample, the corresponding color characteristic breast. There was no difference for the values were averaged, and Pearson's corre- TBARS and the percentage moisture between the two groups (Table 1). Total pigment, myoglobin, and iron concentrations were significantly lower in the pale 4 breast meat as compared with the normal Analytical Software, St. Paul, MN 55113. breast meat (Table 1). 5SAS Institute, Cary, NC 27513.
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
a b
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BOUUANNE ET AL.
TABLE 2. Pearson's correlation coefficients between color values and total pigment concentration, myoglobin, and iron contents for chicken breast meat Color values
Total pigment concentration
Myoglobin content
Iron content
L a b
-.81" .60" -.63"
-.52* .54* -.46*
-.52* .68" -.25
*P £ .05. **p <; .01.
tively. A similar correlation has been reported by Barbut (1993) and van Hoof (1979), who made measurements in light to dark turkey breast meat. These authors suggested that apparent pale color in poultry meat is associated with lower pH and is similar to the PSE condition in pork meat. The post-mortem physical environment of muscle was examined as a potential cause for meat paleness. Observations made in the processing plant revealed that deboned breast fillets from chilled carcasses were stored in boxes lined with plastic bags and filled with ice. These fillets were then held at 4 C in boxes for a minimum of 24 h, and up to 78 h before sampling. Moisture uptake and consequent "dilution" of pigments cannot explain difference in discoloration, as there was no difference in percentage moisture between the two groups. However, moisture uptake on the surface of the fillets was not tested, dilution of the pigments on the surface could be another probability. It is possible that prolonged contact with melt water favored release of meat pigments, therefore causing the meat to look paler. It was indeed observed that water present in the bottom of the boxes had a light pink color after storage. Sample collection was performed on a conveyor belt after storage in containers and before packaging, and thus was considered to be randomized. This study did not verify whether location of the meat in boxes, i.e., top or bottom, and time spent in storage affected meat paleness, but this warrants further investigation. Fleming et al. (1991) reported no difference in heme pigment levels between ice-slush-chilled and airchilled chicken carcasses. They, however, chilled the whole carcass before deboning
Downloaded from http://ps.oxfordjournals.org/ at Michigan State University on February 14, 2015
The reason for difference in pigment concentration between the two groups is unknown. Ante-mortem factors such as preslaughter excitement, heat stress, and free struggle have been reported to increase meat redness (Froning et al, 1978; Ngoka et al, 1982). Myoglobin has also been shown to vary with age and sex in turkeys, therefore affecting meat color (Froning et ah, 1968). As all broiler chickens were approximately the same age when processed, this factor cannot account for paleness of breast meat used in this study. It is, however, unknown whether sex played a role in predisposing chicken breast meat to paleness in this study. There was no correlation between TBARS values and heme pigment concentrations. It has been suggested that difference in concentrations of heme pigments from stored, raw muscles of three species affects TBARS values (Rhee and Ziprin, 1987). The variation in amounts of pigments in the two groups of muscle may not have been great enough to cause a difference in TBARS values. It is also possible that TBARS values and total pigment would have been more closely related in muscle stored for a longer period of time. There were significant negative correlations between L color value and total pigment, myoglobin, and iron concentrations (Table 2), indicating that the decrease in pigment concentrations increased meat lightness. The a color value was positively correlated with total pigment, myoglobin, and iron concentrations (Table 2). This finding seems reasonable, as the a value measures meat redness. There was a significant correlation between L value and pH of -.51 and -.44 (P < .01) for the pale and normal meat, respec-
1697
PALENESS OF CHICKEN BREAST MEAT
and analysis and did not test the effect of ice-slush storage on deboned chicken fillets. Total pigment values appear two to three times higher than those reported in the literature (Ngoka et ah, 1982; Fleming et al, 1991). The present authors cannot explain this difference, which was consistent over the study period. Normal breast myoglobin values were similar to that reported by Fleming et al. (1991) for ice-slush-chilled chicken breast.
1 2 3 4 5 a value (cut-points)
The second objective of this study was to develop an effective method that would objectively discriminate normal from pale chicken meat. Considering each parameter of the CIELAB Color System as a test, the sensitivity (Se) and specificity (Sp) of the L, a, and b characteristics were calculated for a set of cut-points (Figures 1 and 2). For a particular test, the cut-point associated with the optimum combination of Se and Sp gives the highest value. The test is usually interpreted as good if, at that cut-point, both Se and Sp are reasonably high. The choice of an appropriate cut-point remains, however, entirely dependent on the desire to maximize Se only, Sp only, or both of these test characteristics. When the maximum efficiency criterion is applied to the analysis of each color parameter, results indicated that the L color characteristic was
b value (cut-points) --Sensitivity
"O" Specificity
FIGURE 2. Sensitivity and specificity of a and b values when measuring color of normal and pale chicken breast meat. Sensitivity and specificity distribution of a and b values obtained from spectrocolorimetry. The prevalence of pale chicken breast meat is set to 50%.
relatively the best test to discriminate pale from normal meat (Figure 1), whereas the a and b characteristics presented much lower discriminant abilities (Figure 2). In our experimental setting, for example, if the L test were to be used at its maximum 5 -6 efficiency, the cut-point value for L could be set at 56.3 L units where Se and Sp are both £ •« 92%. However, if the Se of the L test is prioritized (minimizing the percentage of pale meat classified as normal), one appropriate cut-point could have been set to 0 52.8 L units, giving a Se of 100% and a Sp of 40 42 44 46 48 SO 52 54 56 58 60 62 64 66 68 70 L v a l u e (cut-points) 56%. Interestingly, these calculations show that the lightness of the meat, over its ^Sensitivity ^Specificity redness or its yellowness, is what the FIGURE 1. Sensitivity and specificity of L value human eye detects when judging a pale when measuring color of normal and pale chicken meat. breast meat. Sensitivity and specificity distribution of L The results suggest that the paleness of values obtained from spectrocolorimetry. The prevalence of pale chicken breast meat is set to 50%. boneless chicken breast stored in ice slush
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might be due to leakage of heme pigments in water. Moisture content values of pale and normal meat were not different, and therefore moisture uptake could not account for the difference in total pigment, myoglobin, and iron concentrations. Analyses of L, a, and b values revealed that L values could be used with high sensitivity and high specificity when used to distinguish pale from normal samples.
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