Effect Of Ultrasound Pre-treatment On The Nutrition And Structure Properties Of Myofibrillar Protein

Grass carp is one of the higher yield of freshwater fish in China, and its protein content is rich. Myofibril protein(MP) is the main composition of fish protein, and has important effects on the fish processing. But because of its poor thermal stability and solubility, and worse gel features than ocean fish, extensive application of fish protein is seriously restricted. In order to improve the function properties of the myofibril protein and improve the utilization rate of grass carp, it is necessary to modify grass carp protein. In this paper, myofibril protein as raw material, ultrasonic technology was applied to the modification. Effect of ultrasonic treatment on the physical and chemical properties and forces between the molecules was studied, and ultrasonic modification mechanism was preliminarily discussed. At the same time, influence of the ultrasonic on myofibril protein gel was studied, and the mechanism of gelation was preliminarily explored. Results are as follows.1. Emulsification and foaming ability of ultrasonic treated myofibril protein were significantly improved, compared with untreated sample. Emulsification increased as ultrasonic power and ultrasonic time increased, foaming ability increased at first then decreased. The proposed reason may be that protein molecules unfolded after ultrasonic treatment, and surface hydrophobicity enhanced, particle size decreased. After ultrasonic treatment, viscosity of myofibril protein solution decreased, thermal denaturation temperature increased and heat enthalpy decreased. Structure stability of myofibril protein molecular is improved. Ultrasonic treatment did not cause any change of protein molecules weight and nutrition.2. The particle size of myofibril protein decreased after treated by ultrasonic; particle size distribution was more homogeneous and the endogenous fluorescence intensity was reduced, hydrophobic sites buried in the molecule gradually exposed, leading to increasing surface hydrophobicity. Ultrasonic weakened the function of heating on degeneration and aggregation of myofibril protein in diluent solution, and inhibited the covalent and non covalent crosslinking in diluent solution between protein and protein. The content of sulfhydryl groups were declined after treated by ultrasonic.3. The intensity of ultraviolet absorption of the myofibril protein solution increased after treated by ultrasonic; the alpha helix and beta folded structure content decreased, while beta turn and random curl content increased. This indicated that ultrasonic treatment weakened rigid structure and enhanced the flexible structure of myofibril protein molecules, molecular became disordered, and secondary structure changed.4. Texture properity such as gel strength, hardness, viscosity, chewiness and water and oil holding capacity of myofibril protein treated by ultrasonic was better than non-ultrasonic myofibril protein. Gel strength increase from 57.41±1.34 g to 57.41±2.86 g. Myofibril protein gel properties mixed with the soy protein isolate is better than that of myofibril protein alone. Mixed gel properties prepared from myofibril protein treated by ultrasonic was enhanced, and had the best gel characteristics at the power of 600 w.5. The sulfhydryl group decreased after treated by ultrasonic. Environmental scanning electron microscopy(SEM) image shown that myofibril protein gel became more fine, dense and uniform after ultrasonic treatment, and had better quality. Ultrasonic samples had lower viscosity, shear rate and shear stress of samples presented nonlinear relationship, namely, the solution was non-newtonian fluid. G ’ and G " were obviously higher than untreated sample, while tan sigma values were less. Dynamic viscoelasticity test shown the three steps of the formation of myofibril protein thermal gels. Namely: gel formation, gel cracking, gel strengthening, and temperature range of each stage was 20 ~ 46 ℃, 56 ~ 46 ℃, 56~85 ℃. The value of G ’was always higher than G " in the whole heating process, indicating that elastic components were more than viscous component during the forning process of protein gel network structure. G ’and G "were higher than non-ultrasonic samples in the heating process, and the bigger the ultrasonic power, the more obvious this phenomenon, indicating that ultrasonic treatment lead to better elastic gel network structure.