Diversity of phenolics including hydroxycinnamic acid amide derivatives, phenolic acids contribute to antioxidant properties of proso millet

Profile of phenolic compounds and antioxidant activity of proso millets were studied. Twelve phenolic derivatives were identified in the free extract, including N′-caffeoyl-N″-feruloylspermidine, N′, N″-dicaffeoylspermidine and N-(p-coumaroyl) serotonin reported for the first time in proso millets. Fifteen phenolic acid derivatives were found in the bound fraction with p-coumaric acid and ferulic acid being the major phenolic acids, as well as four ferulic acid dimers (DFAs) detected for the first time in proso millets. The total phenolic content (TPC) of the soluble and insoluble phenolic fractions varied from 592 to 1510 mg ferulic acid equivalents (FAE)/kg dry weight (DW) and 1146–2436 mg FAE/kg DW, respectively. The total flavonoid content (TFC) of the proso millets ranged from 284 to 978 mg rutin equivalents (RE)/kg DW. DPPH, ABTS and FRAP assays were applied to determine in vitro antioxidant activities for all the phenolic extracts, and the antioxidant levels were attributed to TPCs. The diverse phenolics contributed to the antioxidant properties of proso millet, which can serve as viable functional food ingredients.