Mechanism Of Thermal Aggregation Of Mixed Myofibrillar Protein And Myosin From Hypophthalmichtys Molitrix And Nemipterus Virgatus

Hypophthalmichtys molitrix and Nemipterus virgatus were researched as raw materials.This paper was focused on the investigation of the effect of different ratios on the gel properties,water holding capacity,whiteness,water distribution and composition,thermal stability,Raman spectra,microstructure and Sodium dodecyl sulfates-polyacrylamide gel electrophoresis spectra of mixed myofibrillar protein gels.Additionally,the changes in particle size,turbidity,surface hydrophobicity,free sulfhydryl content,microstructure,secondary structure of protein,tryptophan intrinsic fluorescence spectrum and ultraviolet spectrum of mixed fish muscle myosin were also studied before and after two-step heating(40°C/30 min,90°C/20min).This paper is aimed to understand the synergistic mechanism about thermal aggregation of Hypophthalmichtys molitrix and Nemipterus virgatus myofibrillar protein.Moreover,it also provides an evident theoretical foundation for the development of high-value utilization technology of freshwater fish.Results of this study were as following:1.When the mixed mass ratio of Hypophthalmichtys molitrix and Nemipterus virgatus was 3:1 and 5:1,the gel strength and water holding capacity of mixed myofibrillar protein extracted reached optimum level,and the whiteness of mixed myofibrillar protein gel under the same conditions was close to that of pure Hypophthalmichtys molitrix myofibrillar protein gel.Meanwhile,the mixed myofibrillar protein hadthe highly thermal stability when the mixed mass ratio was 3:1 and 5:1.The network structure of mixed myofibrillar protein gel was uniform and ordered,which was consistent with the change of gel strength.Additionally,myosin was the main protein involved in gel formation and disulfide bonds mainly contributed to the formation of cross-linking.2.The particle size,turbidity,surface hydrophobicity,free sulfhydryl group and appearance morphology of myosin in each experimental group were not significantly different before heating.The main characteristics were as follows: uniform particle size distribution,lower turbidity and surface hydrophobicity,higher free sulfhydryl contents,and myosin was mostly present in the form of monomer according to microstructure analysis.After the process of two-step heating,the particle size of myosin significantly in 5:1 and 1:0 groups increased,and the changes of turbidity and surface hydrophobicity also showed the same trend.The free sulfhydryl group decreased,and the 5:1group had the largest decline compared with other groups.Additionally,microstructural images proven that myosin formed large aggregates.3.The secondary structure of myosin in natural state was mainly?-helix and ?-sheet before heating.The maximum fluorescence intensity,fluorescence peak wavelength of tryptophan and the intensity of characteristic absorption band of UV spectrum in all experimental groups were different.The microstructure of myosin illustrated that myosin existed as monomer or oligomer.After two-step heating,the ?-sheet content of myosin increased,accompanied by a loss of fluorescence intensity in all experimental groups.Myosin was cross-linked and formed a large area of aggregates,especially in the 5:1 group.