Food grade fungal stress on germinating peanut seeds induced phytoalexins and enhanced polyphenolic antioxidants.

The effects of food grade fungus Rhizopus oligosporus stress on phytochemicals and phytoalexins of germinating peanut seeds were investigated by comparing the metabolic profiles of ungerminated (UG), germinated (G), and germinated seeds under fungal stress (GS). Three types of peanut seeds with different skin color (red, reddish brown, and black) were compared in the process. The polyphenolic contents were analyzed and correlated with antioxidant capacity for specific free radicals including peroxyl radical ROO• (ORAC), hydroxyl radical HO• (HORAC), superoxide radical O2•– (SORAC), and DPPH radical. The polyphenolic fingerprints analyzed by HPLC and LC-MSn showed that phenolic acids (coumaric, sinapinic, and ferulic acids derivatives) were the major group of phenolic compounds in ungerminated seeds. G or GS increased the level of phenolic acids, phytoalexins, and antioxidant capacity values in reddish and red peanuts but not in black peanuts. From the LC-MSn spectral data, 45 compounds were identified ten...