Effect of Protein Glutaminase on the Interface Properties of Zein

To improve the application of zein in the food industry, the present study explored the effect of adding different amounts (0, 10, 20, 30, 40, and 50 U/g) of protein glutaminase (PG) on the interfacial properties of zein by measuring solubility, protein structure, surface hydrophobicity, foaming, emulsification, surface tension, surface expansion modulus, and other indicators. As the amount of PG added was increased, the degree of zein deamidation gradually increased. When the amount of enzyme added was 40 U/g, the solubility increased by 504.38% compared with that of the control group. The secondary structure results showed that PG reduced the relative content of β-sheet and increased the relative content of β-turn. The endogenous fluorescence intensity and surface hydrophobicity first decreased and then increased, and the microstructure changed from blocks to flakes, forming a regular three-dimensional (3D) network structure. Raman spectral analysis showed that the peak intensity ratio of tyrosine residues (I850/I830) was enhanced, whereas the peak intensity ratio of tryptophan residues (I760/I1004) first decreased and then increased. In addition, PG reduced the surface tension of zein at the air-liquid interface, enhanced its surface expansion modulus, and significantly (P<0.05) improved its emulsification and foaming properties. In summary, the present study showed that PG treatment can change the structure of zein, improve its interfacial properties, and enhance its functional properties, which enables the improved use of zein in the food industry.