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

Actomyosin (AM, 5mg/ml) extracted from ordinary (white) muscle of tilapia (Orechromis niloticus) was subjected to thermal treatments (25-95 degrees 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 degrees 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 degrees C were still soluble in 0.6 mol/l KCI-20mmol/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 degrees C treatments, and those decreased almost 50% by heating at 95 degrees C. Total sulfhydryl groups (T-SH) contents of AM decreased with elevating temperatures. This study revealed that thermal treatments beyond 45 degrees C induced AM to form a cluster of aggregates with noncovalent bonds; however, those beyond 75 degrees 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. (C) 2006 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.