Study on heat-induced aggregation and gelation behaviours of myofibrillar protein/casein mixtures

In this study, the aggregation and gelation behaviours of heat-induced fish myofibrillar protein (MP)/casein mixtures prepared with different mixing ratios (MP: casein = 1:0, 5:1, 1:1, 0:1) were investigated. The rheological results showed that casein significantly affected the rheological behaviour of MP, and the storage modulus decreased as the mixing ratio changed from 1:0 to 0:1. Results in turbidity, particle size, scanning electron microscopy, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis indicated that MP and M:C = 5:1 groups exhibited higher cross-linking aggregation, especially under high-temperature heating. From 40 °C to 90 °C, the mixed systems showed higher total sulphydryl contents and bromophenol blue binding amounts (p < .05) compared with individual systems, suggesting that hydrophobic interaction and disulphide bonds were probably the main forces for the formation of binary MP-casein complexes. Additionally, the M:C = 5:1 group presented an obvious transition from α-helix to β-sheet, with the α-helix decreasing from 15.58% to 9.00% and β-sheet increasing from 48.68% to 57.62%. Overall, when the mixing ratio of MP to casein was 5:1, it was more conducive to the formation of a superior gel network. The present study helps to elucidate the correlation between protein aggregation behaviours in solution and the network structure in gel, providing a theoretical basis for the textural regulation of gel food based on a binary protein system.