Free Phenolic Acids in Shanxi Aged Vinegar: Changes During Aging and Synergistic Antioxidant Activities

Shanxi aged vinegar (SAV) is the most famous one among the four typical famous vinegars in China, which is produced by spontaneous solid-state fermentation using sorghum, bran, and millet chaff and Daqu. In this study, free phenolic acids (FPAs) species and changes during SAV aging, and the synergistic antioxidant activities between FPAs was investigated. The results revealed that eight FPAs, including protocatechuic acid, p-hydroxybenzoic acid, salicylic acid, dihydro sinapic acid, p-coumaric acid, sinapic acid, dihydro ferulic acid, and ferulic acid, stably existed during SAV 0–5 year aging periods, whereas during the aging time evaporation of water and FPAs combining with melanoidins made prediction of precise FPAs contents difficult. With regard to FPAs synergistic antioxidant activities, it was observed that the FPAs antioxidative interrelations were antagonism in antiradical activity experiments. And, only a few groups of FPAs mixtures showed antagonism in reduction experiments.