Effect of aging, thawing and frozen storage on the tenderness of chicken broiler muscle

The effects of various aging, thawing and storage methods on the tenderness of frozen broiler Pectoralis major muscle were studied. Initial experiments were carried out to establish standard methods of freezing, cooking and tenderness evaluation to be used in subsequent experiments. The effects of varying the aging, thawing and storage techniques were then investigated using the established methods. Whole carcasses were frozen in a liquid nitrogen blast freezer after cooling in ice water for periods of 1 to 10 hours after slaughter, stored for 1 week at -31°C and thawed for varying lengths of time. The P. major muscles were removed and cooked in boiling water between metal plates. Tenderness evaluations were carried out using the Allo-Kramer shear press. The length of thawing time was shown to greatly influence the degree of toughness of the cooked muscles. When a thawing period of 4 hours in water at 25°C was used, a decrease in toughness took place in carcasses frozen between 1 and 2 hours post-mortem. This was followed by an increase to maximum toughness in birds frozen between 4 and 8 hours post-mortem. Maximum tenderness occurred in birds frozen 10 hours after death. Thawing birds in air at 4°C for 24 and 4 8 hours decreased the level of toughness attained after freezing 4 to 8 hours post-mortem. It did not significantly alter the degree of tenderness reached after 10 hours. Similarly, the decrease in toughness in birds frozen between 1 and 2 hours post-mortem, remained significant. Longer storage (3 months) at -23°C followed by rapid thawing eliminated both the decline in toughness of carcasses frozen between 1 and 2 hours post-mortem and the maximum toughness level attained by carcasses frozen 4 to 8 hours after death. An attempt was made to explain the decrease in toughness in carcasses frozen between 1 and 2 hours postmortem in terms of the aging temperature and medium used prior to freezing. No difference in the pattern was observed, however, when other pre-freezing aging techniques were used. Increases in the sarcomere lengths of muscle frozen at 2 hours post-mortem were observed, corresponding to the increase in tenderness occurring in carcasses frozen at this time. Isometric tension measurements, however, did not correlate well with these observations. Taste panel members were unable to discern differences in the tenderness of muscle frozen between 1 and 3 hours post-mortem although excellent correlations were obtained between Allo-Kramer shear press values and sarcomere length measurements. The results of these experiments therefore show that the ultimate tenderness of broiler muscle can be greatly influenced by the interaction of pre-freezing aging time, length of storage and thawing techniques used prior to cooking.Land and Food Systems, Faculty ofGraduat