Mobility and redistribution of waters within bighead carp (Aristichthys nobilis) heat-induced myosin gels

Water-holding capacity is closely related to gel microstructure, and is a very important quality trait in surimi and surimi product. The changes in the secondary structure, gel microstructure, and the migration of water in bighead carp (Aristichthys nobilis) myosin gel induced by different temperatures (50–90°C) were investigated. The α-helical structure of myosin decreased at temperatures of 40°C or higher. The fractal dimension of the gels increased at 40, 50, and 60°C, but decreased at temperatures over 60°C. The pore size of the gels increased with temperatures up to 50°C, decreased at 60°C, and then increased with temperatures up to 90°C again. The transverse relaxation times also varied; T21 remained constant at temperatures over 40°C; T22 decreased at temperatures lower than 50°C, increased at 60°C, and then decreased with temperatures up to 90°C; and T23 increased at temperatures lower than 50°C and then remained constant until 90°C. Principal component analysis showed that the proportion of T22 water (PT22) was inversely correlated with the unfolding of myosin, whereas directly correlated with the pore size. The proportion of T23 water (PT23) was positively correlated with the fractal dimensions of the gels, whereas negatively correlated with the pore size. The migration of the secondary layer of water was mainly caused by hydrophobic force and the physical space formed by the myosin backbone, and the migration of water within the third layer was mainly caused by capillary pressure. Therefore, the mobility and redistribution of waters depend on the water retention mechanism, which is determined by the physical structure of gels. This study provides further information about the relationship between the NMR data, gel microstructure, water mobility, and distribution.