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.

Effects of the incorporation of ultrasound with varied intensities (0-800 W) into the thermal-induced gelation process on the gelling properties of myofibrillar protein (MP) were explored. In comparison with single heating, ultrasound-assisted heating (<600 W) led to significant increases in gel strength (up to 17.9%) and water holding capacity (up to 32.7%). Moreover, moderate ultrasound treatment was conducive to the fabrication of compact and homogenous gel networks with small pores, which could effectively impair the fluidity of water and allow redundant water to be entrapped within the gel network. Electrophoresis revealed that the incorporation of ultrasound into the gelation process facilitated more proteins to get involved in the development of gel network. With the intensified ultrasound power, α-helix in the gels lowered pronouncedly with a simultaneous increment of β-sheet, β-turn, and random coil. Furthermore, hydrophobic interactions and disulfide bonds were reinforced by the ultrasound treatment, which was in support of the construction of preeminent MP gels.

To investigate the role of sulfhydryl groups and disulfide bonds in different protein-stabilized emulsions, N-ethylmaleimide (NEM) was used as a sulfhydryl-blocking agent added in the emulsion. The addition of NEM to block the sulfhydryl groups resulted in a reduction in disulfide bond formation, which enabled the internal structure of the protein molecule to be destroyed, and then decreased the restriction of protein membrane on the oil droplets. Furthermore, with the NEM content increasing in the emulsion, a reduction in the protein emulsifying activity and emulsion stability also occurred. At the same time, the intermolecular interaction of the protein on the oil droplet interface membrane was destroyed, and the emulsion droplet size increased with the NEM content in the emulsion. Although NEM blocking sulfhydryl groups from forming disulfide bonds has similar effects on three types of protein emulsion, the degree of myofibrillar protein (MP), egg-white protein isolate (EPI), and soybean protein isolate (SPI) used as emulsifiers had a subtle difference.