Glycogen debranching enzyme and some other factors relating to post‐mortem pH decrease in poultry muscles

The objective of this study was to investigate the activity of glycogen debranching enzyme (GDE, EC 3.2.1.68) in chicken pectoralis superficialis (PS) and quadriceps femoris (QF) muscle post‐mortem. In addition, some other factors relating to pH decrease, such as the activity of glycogen phosphorylase (EC 2.4.1.1) and glycolytic potential were studied. Enzyme activities, glycogen content and lactate content were measured in Ross breed broiler chicken muscles obtained 25 min after stunning. An interesting discrepancy in the activities of the two glycogen degrading enzymes, GDE and phosphorylase, between muscles was found. In light PS muscle, phosphorylase activity was higher (P < 0.001), but GDE activity was lower (P < 0.001) than in dark QF muscle. Buffering capacity and glycolytic potential were higher in PS muscle than in QF muscle. The possible need for high buffering capacity and low GDE activity in PS muscle to protect living muscle from rapid pH decrease was discussed. GDE, together with glycolytic potential, accounted for 40% of the variation in ultimate pH in QF muscle and 61% in PS muscle. Considering the low activity of GDE together with the high activity of phosphorylase found in both muscles, the results of the present study support the hypothesis that GDE may restrict the rate of glycogen degradation. Copyright © 2006 Society of Chemical Industry