Protein structure and sulfhydryl group changes affected by protein gel properties: process of thermal-induced gel formation of myofibrillar protein

The study investigated the change in protein structure upon thermo-induced gelation of myofibrillar protein (MP, 2%) under different temperatures (30–80°C) at 0.6 M NaCl and pH 6.2. The results showed that heating from 45°C led to changes in physicochemical properties and intermolecular forces involved during MP gelation, which are related to each other. During the heating process, the free sulfhydryl content slowly increased and reached the highest value at 45°C (10.23 ± 0.13 μmol/g protein). When the temperature exceeded 50°C, Ellman's titration and SDS-PAGE results indicated that MP gel began to form with the formation of disulfide bonds, which contributed to stabilize the gel structure. Gel strength of the heat-induced MP gel formed at 60°C was significantly higher than that at other temperatures (P < .05), reaching 1.12 ± 0.02 N. Strictly speaking, myofibrillar protein gelatinized after 60°C, and water-holding capacity of the MP gel decreased from 60-80°C, and reached a relatively low value at 80°C. Furthermore, Raman spectra showed that the α-helix content decreased with increasing temperature, β-sheets and random coil contents increased, and the content of the twist-twist-trans conformation increased steadily.