Liberation of peptides during meat storage and their interaction with proteinase activity

The content of nitrogenous material extracted in perchloric acid from kid longissimus lumborum (LL), semimembranosus (Sm) and triceps brachii (TB) muscles increased 30% during storage for three weeks at 4 °C. The extract of fresh muscle contained a range of molecular sizes up to 13 kDa, the majority less than 4 kDa. The amount of the larger polypeptides (> 4 kDa) extracted from meat decreased to 50% of its initial level in meat stored for five days and to 20% after 25 days. The amount of intermediate sized peptides (1.9 to 4 kDa) remained largely constant throughout storage of meat of normal pH, whilst in meat of high ultimate pH, they showed a transitory increase during the first two weeks storage. Smaller size peptides increased with storage time; increasing more slowly in meat of high ultimate pH. This time-dependent pH effect indicates a sequential autolysis involving neutral followed by acidic proteolytic and peptidic activity. Calpain from beef muscle degraded peptides in the extract and the extract acted as a competitor against a synthetic substrate. This implies that the in-situ autolysis and tenderisation of meat postmortem could be reduced by peptide products.