Effects of actomyosin dissociation on the physicochemical and gelling properties of silver carp myofibrillar protein sol during freeze–thaw cycles

Myofibrillar protein (MP) system with different dissociation degrees of actomyosin was constructed by addition of ATP and the effects of actomyosin dissociation on the physicochemical and gelling properties of MP sol during freeze-thaw cycles were investigated. The results showed that the salt soluble protein content of the dissociated sample with 5 mM ATP (5-pH 6.2 group) was lower than that of other groups under unfrozen state, while the fluorescence intensity and hardness of all dissociated groups were significantly lower (P＜0.05) than that of the control group. After five freeze-thaw cycles, the low-field nuclear magnetic resonance (LF NMR) revealed that the immobile water (T22b) in MP sol with 5 mM ATP (pH 6.9) has lower fluidity compared with the control group. In addition, rheological studies revealed that the G' (storage modulus) value at 90℃ of MP sol with 5 mM ATP (pH 6.9) showed less decrease than that of the other groups after five freeze-thaw cycles. Meanwhile, after five freeze-thaw cycles, scanning electron microscope (SEM) showed that the gel of the control group has large holes and rough structure, while the microstructure of sample with 5 mM ATP (pH 6.9) was more compact and uniform. The heat-induced gel of 5-pH 6.9 group had highest hardness and lowest cooking loss among the groups after five freeze-thaw cycles. Briefly, the dissociation of actomyosin before freezing could slow down the rate of MP denaturation and improve the gelling properties after freeze-thaw cycle.