Microbial transglutaminase promotes cross-linking for enhancing gelation of myofibrillar protein in frozen Litopenaeus vannamei through deamination reaction

In this paper, the effects of different microbial transglutaminase (mTGase) treatments (0–0.5% w/w) on the structural and functional characteristics of frozen shrimp (Litopenaeus vannamei) were investigated to explore the changes in myofibrillar protein (MP) during the catalytic process of mTGase, and further enhance the gel properties of shrimp surimi products. Fourier transform infrared spectroscopy showed that mTGase treatment caused a shift from α-helix to β-turn and β-sheet in the secondary structure of the protein, while chemical force results indicated that moderate addition of enzyme could promote the formation of disulfide bonds in the gel system, contributing to the formation of a stable three-dimensional spatial structure. These structural changes led to a significant increase in gel strength, WHC and storage modulus (G′) after mTGase-induced protein gelation, resulting in an increase in the solid properties of the gel; and the relaxation time T22 was significantly shortened, indicating a gradual decrease in water freedom in the protein gel network. In addition, scanning electron microscopy results showed that the gel with 0.4% mTGase had a denser network structure and more uniform pores. Simultaneously, mTGase facilitated the reduction of free amino groups through deamination reaction, resulting in an elevated cross-linking degree and a reduced hydrolysis rate of pepsin. The above results indicated that appropriate mTGase treatment could improve the structure and functional properties of shrimp, benefit the quality of shrimp surimi products, and provide some references for the highly processed frozen Litopenaeus vannamei.