Cellular antioxidant activities of phenolic extracts from five sorghum grain genotypes

Measurement of antioxidant activity using biologically relevant methods is important for screening natural products for their potential health product development. The cellular antioxidant activities (CAA) based on Caco-2 cells and in vitro antioxidant activities (IAA; including ABTS, DPPH and FRAP assays) of free and bound phenolic extracts from both bran and kernel fractions of five coloured sorghum grain genotypes were examined. The CAA results were highly consistent with the IAA results, and both demonstrated a phenolic concentration dependent manner and were highly correlated with the contents of flavonoids (3-deoxyanthocyanidins and flavanones) and tannins (proanthocyanidins). The antioxidant activity of sorghum grain was mainly contributed by its readily extractable free form phenolics from the bran. Brown and black sorghums showed potent antioxidant activity, in which the brown-bran-free and black-bran-free phenolic extracts had the highest antioxidant activity. In addition, the black-bran-free phenolics had high cellular antioxidant quality, and the brown-bran-free phenolics had a high degree of the cell membrane and intracellular antioxidant effects. This study first investigated the CAA of sorghum phenolic extracts and the results demonstrated that brown and black sorghum bran has great potential to be developed as a natural antioxidant for food and nutraceutical applications.