Development of Muscle Thermal Rigorometer and Characterization of Heat-induced Muscle Shortening of Tilapia

A muscle thermal rigorometer was constructed, allowing muscle shortenings induced by dynamic heating or isothermal aging to be monitored. Operating isothermally like a traditional rigorometer at 10 °C, postmortem dorsal muscle shortening (S_10°C) developing from 0% to 10% of its initial length in corresponding to RI_fiber along fiber‐direction developing from 0% to 100% within 16 h was monitored for freshwater tilapia. Monitoring meat cooking in the dynamic heating mode, heat‐induced shortenings could be observed for all muscle samples possessing different degrees of rigor induced by 10°C aging. The heat‐induced shortening (S_dynamic) plus its 10°C aging shortening (S_10°C) for each sample was the same, S_overall= S_10°C+ S_dynamic= 10%. Their heat‐induced shortening peak temperatures (Ts) from 30°C to 48°C were inversely correlated with the sample RI_fiber from 0% to near 100%. These findings together with an additional calcium/adenosine triphosphate (ATP) model studies showed that the ATPase related myofibrillar contractile system was responsible for these low‐temperature cooking shortenings, which along with Ts values could thus be adopted as new rigor indices.