Effects of various sterilization treatments on the structural and functional alterations of the epigallocatechin-3-gallate-casein complex.

The effects of dairy sterilization techniques (65 °C/30 min, 72 °C/15 s, 85 °C/15 s, 100 °C/5 min, and 121 °C/5 s) on the epigallocatechin-3-gallate-casein (EGCG-CS) complexes were investigated through the structural and functional characteristics in this work. Fourier transform infrared spectroscopy (FT-IR) detection showed the redshirting of the absorption peak suggested structural changes in the amide I area. Field emission scanning electron microscopy (FESEM) and viscosity measurements proved that treatments above 85 °C broke non-covalent bonds, leading to instability and low viscosity of EGCG-CS. Moreover, the values of surface hydrophobicity, solubility, and sulfhydryl group content appeared the same phenomenon of first rising then falling at higher temperatures, resulting from the CS protein exhibited obvious peptide chain stretch and hydrophobic residue exposure. Notably, the 15-s thermal treatment at 85 °C enhanced the structural stability, foaming, and emulsifying abilities of the EGCG-CS complexes, providing important technology information for industrial applications.