Cross-linking activity of oxidised tannic acid towards mackerel muscle proteins as affected by protein types and setting temperatures

Cross-linking activity of oxidised tannic acid (OTA) at different levels (0–0.3% of protein content) towards natural actomyosin (NAM), sarcoplasmic protein (SP) and NAM/SP (65:35) mixture from mackerel (Rastrelliger kanagurta) muscle incubated at different temperatures for 30 min was investigated. NAM solution showed an increase in turbidity, surface hydrophobicity and disulphide bond contents as OTA added increased up to 0.2%. The higher aggregate formation of NAM solution containing 0.2% OTA was found when incubated at 40 °C, compared with at room temperature (26–28 °C). The lower aggregation of NAM was noticeable in the presence of SP, which was more preferably cross-linked by OTA via weak bonds. Thus, SP showed the interfering effect on NAM cross-linking induced by OTA. Myosin heavy chain (MHC) band intensity was decreased and a highly ordered dense protein network of NAM was obtained when 0.2% OTA was incorporated. Conversely, coagulation was formed in the NAM/SP mixture added with 0.2% OTA. Thus, the cross-linking efficiency of OTA varied with the type of muscle protein and setting temperature.