Abstract: The microscopic features of riboflavin-binding peptide, prepared from the pine nut peptide Ac-QWFCT and riboflavin, were examined by scanning electron microscope, and the immunomodulatory activity was evaluated by measuring cell viability, neutral red phagocytosis rate and NO production. Moreover, the antioxidant activity was evaluated by determining the scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radicals, and Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance were used to determine the interaction between the peptide and riboflavin. The absorption characteristics of riboflavin-binding peptide were studied by the rat everted gut sac method. The results showed that the microstructure of Ac-QWFCT changed from reticular to flocculent after binding with riboflavin. The neutral red phagocytosis rate and NO release rate of riboflavin-binding peptide were higher than those of Ac-QWFCT and riboflavin, reaching the maximum value at a concentration of 25 μg/mL. At 0.1 and 0.2 mg/mL, the DPPH radical and ABTS cation radical scavenging capacities of riboflavin-binding peptide were significantly higher than those of Ac-QWFCT and riboflavin. Tryptophan and phenylalanine residues in the peptide bound to riboflavin through hydrophobic interactions. Binding to the peptide Ac-QWFCT could increase the absorption of riboflavin in the intestine of rats. This study can provide a theoretical basis for the development of new vitamin B2 supplements.

Key words: pine nut peptide; riboflavin; immunomodulatory activity; antioxidant activity; structural characterization