RELATIONSHIP BETWEEN RATE OF POST-MORTEM PH FALL AND AGING OF LONGISSIMUS MUSCLE IN PIETRAIN PIGS

Twenty-six pietrain pigs exhibiting wide variability in pH(45) (pH value 45 min post mortem) values were used to assess the mechanical behaviour of cooked and raw Longissimus muscle at 24 h and 8 days post mortem. Rheological behaviour was studied in compression under strain conditions which allow specific determination of myofibrillar resistance. The muscles were divided into three groups on the basis of pH(45) values: (Severe pale, soft and exudative (PSE), pH(45) = 5.49 +/- 0.03 (n = 9); PSE pH(45) = 5.78 +/- 0.04 (n = 10); Normal, pH(45) = 6.35 +/- 0.05 (n = 7). The three groups did not differ significantly for ultimate pH (pH(u) = 5.57 +/- 0.02 for the 26 muscles). A lower mechanical resistance of raw samples was found in the Normal group, regardless of the time post mortem. Although this difference was not significant, a significant relationship was found between this trait and pH(45) at both times post mortem (r = -0.43, P < 0.05, at 24 h and r = -0.44, P < 0.05, at 8 days post mortem). However, no significant effect of pH(45) was found on the mechanical resistance of cooked muscles. The relative decrease in myofibrillar strength after an 8-day ageing period was not affected by pH(45) but this was due to the fact that the three groups exhibited different starting points. Mechanical resistance of raw; and cooked muscles at 24 h past mortem were significantly related to pH(u) (r = -0.55, P < 0.01, and r = -0.49, P < 0.05, respectively). The present results show that after an 8-day ageing period, PSE muscles are not fully aged.