Effect of delay time before chilling on toughness in pork with high or low initial pH.

Paired M. longissimus dorsi muscles from 56 carcasses of Danish Landrace and Yorkshire breeds, slaughtered at approximately 90 kg live weight, were utilized to study the potential of cold induced toughness in pork. Based upon the pH value 45 min post stunning, the carcasses were divided in two groups: a low (5·7 ≤ pH < 6·1) and a high one (6·1 ≤ pH ≤ 6·5). The effects on Warner-Bratzler shear force, sarcomere length and myofibril fragmentation of inserting a delay time of 0, 2 and 4 h before carcasses entered the chilling tunnel (operating at -28°C to -22°C) were investigated on early excised muscles as well as on muscles removed 30 h post stunning. The left LD muscle from each carcass served as a control while all right sides were used for treatments. pH and temperature measurements obtained from LD muscles left on carcasses during chilling showed that LD muscles belonging to the high pH group involve a risk of cold shortening even when a 2 h delay was used before passing in to the chilling tunnel. Comparing pH groups, however, sarcomere lengths did not differ in control sides whereas the Warner-Bratzler shear force values were significantly higher in LD muscles taken from the high pH group. Early excision of the LD muscle resulted in shorter sarcomere lengths and increased WB shear force only for carcasses belonging to the high pH group, which, however, could be avoided by introducing a 4 h delay time before rapid chilling. The effect of delay time on tenderness from muscles excised from the carcass 30 h post stunning was much less but a 4 h delay did significantly (P < 0·05) improve tenderness in carcasses with high initial pH. Coefficient of correlation between Warner-Bratzler shear force and sarcomere length was -0·12 and nonsignificant in the low pH group, whereas it was -0·57 and highly significant in the high pH group.