Effects of rinsing and mashing on physical and chemical properties of myosin in sea bass

The physicochemical properties, such as total sulfhydryl (T-SH) group, active sulfhydryl (R-SH) group, surface hydrophobicity and turbidity, were determined for the myosin that extracted separately from the raw materials, rinsed- and simmer surimi in sea bass, while the secondary structure and surface morphology of the myosin were analyzed using the combined techniques including the infrared spectroscopy and atomic force microscopy (AFM). The experimental results showed that the content of total sulfhydryl (T-SH) groups in the myosin of the rinsed surimi decreased by 19.5% from 8.51 to 6.85 mol/105 g, whereas the active sulfhydryl group increased by 63.9% from 1.39 to 3.86 mol/105 g, compared with the raw materials. The content of total sulfhydryl (T-SH) and active sulfhydryl (R-SH) groups in the myosin of the simmer surimi decreased to 5.3 and 1.28 mol/105 g compared with the raw materials, indicating decrease by 22.6% and 66.8%, respectively. The ratio of the active sulfhydryl (R-SH) to the total sulfhydryl (T-SH) group in the myosin of the rinsed surimi is the largest than others, inferring that the myosin of the rinsed surimi can be the most deformed in this case. The turbidity and surface hydrophobicity, the indictor for the aggregation and degree of denaturation in proteins, in the myosin of the surimi increased after the treatment of rinsing and simmering. Specifically, the turbidity of the myosin in the surimi increased by 12.5% after rinsing and 22.2% after simmering, compared with raw materials , whereas the surface hydrophobicity increased by 47.9% after rinsing and 5% after simmering. The data reveal that the treatment of the rinsing and simmering can significantly affect the denaturation and aggregation of proteins in the varying level. The rinsing has a greater influence on the surface hydrophobicity, while the mixing effect has a greater influence on the turbidity. The simmering can cause the slight aggregation of the myosin to form a sort of microgel. There was a much more obvious effect of the rinsing on the secondary structure of the myosin. In Fourier transform of the infrared spectroscopy the α-helix relative content of the myosin that extracted can decreased by 33.16%, while the random curl relative content increased by 79.42%, β-fold and β-turn increased by 1.11% and 10.38%, respectively, after the rinsing of raw materials in the sea bream. After rinsing, the change rate of the secondary structure in the surimi myosin was smaller, and the α-helix and random curl content decreased by 1.16% and 7.95%, β-fold and β-turn increased by 4.16% and 1.92%, respectively. Generally, the decrease in the α-helix content can be conducive to the aggregation of proteins, and the increase in β-sheet and β-turn can be beneficial to the formation of the good gel structure. The characterized results from atomic force microscopy (FAM) showed that the myelin myosin exhibited a sort of protein bundle under the natural conditions, and the distribution of the protein bundle in the suspension was uniform without obvious granularity. Both treatment of the rinsing and simmering can change the surface morphology of the myosin in the sea bass, indicating reduce significantly the aggregation clusters of the myosin, while increase the height of the aggregates in the myosin suspension from 14 nm to 25 nm. After mixing, the height of the myosin aggregates did not change significantly. These findings demonstrate that the treatment of the rinsing and simmering have a great influence on the physicochemical properties of the myosin in rinsed and simmer surimi of the sea bass, as well as a certain effect on the degeneration and aggregation of the myosin suspension. This study can be expected to provide potential reference for the future development on the formation mechanism of surimi gel in food industry.