Physicochemical properties and microstructure of fish myofibrillar protein-lipid composite gels: Effects of fat type and concentration

The effects of fat type and concentration on silver carp myofibrillar protein-lipid composite gels were investigated. Two types of pre-emulsification lipids, lard and camellia seed oil were incorporated into myofibrillar proteins (MPs) solution, with final concentrations of 1-3% (based on the solid content of the composite gels). Compared to a gel without fat, composite gels showed significant (P < 0.05) increases in breaking force, deformation, whiteness, water-holding capacity (WHC), storage modulus (G') and loss modulus (G ''). Raman spectroscopy studies showed that there was a decreasing trend in the alpha-helix content and an increasing trend in the beta-sheet, beta-turn, and random coil content in composite gels, and the highest alpha-helix content was found in gels made with 2% camellia seed oil. Changes in disulfide bonds and analysis of the microenvironment relating to tryptophan residues and tyrosine doublet bands also revealed that lipids improved the stability of the gel structure and increased hydrophobic interactions in composite gels, and also, camellia seed oil showed better results than lard, which might due to their differences in emulsifying properties. Microstructure studies revealed that more compact three-dimensional network structures were observed in composite gels containing 2% lard or camellia seed oil than those of the controls. It was concluded that lipids can act as active filler in the MP network, where gel and lipid globules are stabilized by a membrane coating mainly formed by salt-soluble MPs. The mobility of fat and water is likely restricted by physicochemical interactions between protein-coated lipid globules and the protein matrix.