DYNAMICS OF POSTMORTAL PH VALUE VARIATION S IN THE BREAST AND THIGH MUSCLES OF CHICKENS

The objective of the study was to determine individual and group varia bility in postmortal pH values in the breast and thigh muscles of chic kens from standard supplies to a poultry processing plant. pH values a re an adequate indicator of the state and pattern of biochemical postm ortal changes in meat. Increasing quantities of chicken meat processed to make meat products pose a problem of knowing the quality of this b asic foodstuff - of the level, dynamics and variability of postmortal changes. The objective of the study was to determine the dynamics and variability of pH values in two main muscular regions of chickens - br east and thigh muscles. Random sampling of groups of slaughter chicken s supplied to processing on a packing line was used within one year. F ifteen groups with 10 chickens in each were evaluated: five groups of plucked and drawn chickens, five groups after chilling with water and five groups divided into half numbers following the mentioned stages o f dressing. Detailed evaluation in 30-minute intervals showed elementa ry differences between the breast and thigh muscles. pH values in the breast muscle decreased relatively dynamically below 6.0 in the first three hours post mortem, further decrease was minute only (Fig. 1). Th e assumed physiological pH value at the moment of chicken killing is 7 .0, and the first values in the breast muscle in 45 minutes post morte m were close to 6.3. The rigor mortis set in 3 to 4 hours post mortem. The rigor mortis in the thigh muscle was found to terminate 90 minute s post mortem at pH around 6.4. pH values started increasing only afte r this breakpoint, at a very slow rate, to reach pH 6.5 to 6.6 in 7 ho urs after chicken killing. Different pH values in the breast and thigh muscles can have expressive impacts on the hygienic and technological quality of meat - rapid onset of microbial proteolysis in the thigh m uscle, and on the other hand, easier boning and better retention capac ity. The breast muscle is expected to show opposite trends. The dynami cs of pH values in the warm and chilled muscle exhibited identical tre nds. pH values in the muscles of chilled chickens were always only a l ittle higher, which can be explained by moderate inhibiting effects of cold on meat autolysis. Relatively large variability in pH values was determined both between the chicken groups and between the separate c hickens within the groups (Figs. 2 to 5). Trends of variations were id entical, but the differences in average values between the extremely d ifferent groups amounted up to 0.8 pH, and individual differences with in the groups up to 1.0 pH in the thigh muscle and up to 0.5 pH in the breast muscle. Hence the large variability of meat characteristics in chickens from standard supplies can be derived from this study.