Analysis of antioxidant effect of two tripeptides isolated from fermented grains (Jiupei) and the antioxidative interaction with 4-methylguaiacol, 4-ethylguaiacol, and vanillin.

Jiupei (fermented grains) is the raw material for Baijiu distillation. The antioxidant activities of peptides Val-Asn-Pro (VNP) and Tyr-Gly-Asp (YGD) identified from Jiupei were evaluated according to in vitro chemical assays (e.g., 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, 1,1-diphenyl-2-picrylhydrazyl, and oxygen radical absorbance capacity) and 2,2'-azobis (2-methylpropionamide)-dihydrochloride-activated HepG2 cell model. The interaction on antioxidant activities between peptides (VNP and YGD) and three functional phenols (4-methylguaiacol, 4-ethylguaiacol, and vanillin) which were found in Baijiu was also measured. On the basis of the results, two peptides exhibited strong antioxidant ability in oxygen radical absorbance capacity (ORAC) assay. Furthermore, they suppressed the generation of reactive oxygen species. The intracellular antioxidant enzymatic system and nonenzymatic system were also regulated by VNP and YGD. In addition, it was confirmed that partial auxo-action between peptides and phenols appeared mostly in chemical assays. The findings above might indicate that VNP and YGD are potent natural antioxidants in Jiupei even in Baijiu through distillation process and lay the foundation for illustrating the interactions among different functional substances in Baijiu.