Abstract: The fluorescence spectra and antioxidant properties of casein non-phosphopeptides-soybean peptide complex (CNPSPC) prepared under different pH conditions were analyzed. The results showed that with the increase of pH, the content of surface-exposed Trp residues buried in hydrophobic environment in CNPSPC was became lower than in the raw protein, and the microenvironment polarity of Trp residues was decreased. The results of thioflavin T (ThT) fluorescence assay showed that the fluorescence intensity of CNPSPC was maximum at pH 6.0, which represented β-sheet was the dominant secondary structure of CNPSPC. The microenvironment of Trp residues was changed by the assembly, thereby changing the molecular conformation of CNPSPC. Compared with casein non-phosphopeptides (CNPP) and soybean peptide (SP), the antioxidant capacity of CNPSPC was improved. The scavenging activities of CNPSPC against 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide anion and hydrolxyl radicals were maximum at pH 6.0, which increased by 3.34, 1.12 and 1.08 times compared to soybean protein respectively.

Key words: soybean polypeptide, casein non-phosphorylated peptide, assembly, fluorescence spectrum, antioxidant activity