Changes in conformation and sulfhydryl groups of tilapia actomyosin by thermal treatment

Actomyosin (AM, 5 mg/ml) extracted from ordinary (white) muscle of tilapia (Orechromis niloticus) was subjected to thermal treatments (25–95 °C, 10–60 min) to investigate the changes of sulfhydryl groups and conformation. Aggregates of AM were found by the thermal treatments at 42 and 45 °C, and the aggregates could be removed by centrifuging at 15,000g for 5 min. Otherwise, the AM aggregates induced by the other thermal treatments beyond 35 °C were still soluble in 0.6 mol/l KCl-20 mmol/l Tris-maleate buffer (pH 7.0) even after centrifugation. Reactive sulfhydryl groups (R-SH) contents of AM showed the greatest amount in this study by 42 and 45 °C treatments, and those decreased almost 50% by heating at 95 °C. Total sulfhydryl groups (T-SH) contents of AM decreased with elevating temperatures. This study revealed that thermal treatments beyond 45 °C induced AM to form a cluster of aggregates with noncovalent bonds; however, those beyond 75 °C induced AM to aggregate mostly attributed by disulfide bonds. Also, thermal treatments at different temperatures would produce fish protein-related products with various characteristics.