Antioxidant properties of free and bound phenolic acids from bran, spent grain and sorghum seeds

Background and objective Sorghum by-products contain important amount of phenolic compounds and may be used as sources of phenolic antioxidants. This study aims to investigate the phenolic contents and the antioxidant activities of free and bound phenolic extracts from sorghum bran, spent grain, and seeds as potential sources of natural antioxidants agents. Findings Among the six extracts, the free phenolic acids (PA) mixture from bran with the highest total phenolic contents (291.50 ferulic acid equivalents/g flour) showed the highest antioxidant activity with all three tests (FRAP, ABTS, and DPPH). Syringic (0.06-2.65 mg/100 g of flour), vanilic (0.47-2.63 mg/100 g), and p-hydroxybenzoic (0.38-1.75 mg/100 g) acids were the major free PAs. Ferulic acid (1.20-6.37 mg/100 g) was the major bound PA. PA content and composition in the mixtures greatly contribute to their antioxidant activity. Conclusions Free and bound PA from sorghum by-products, especially the free PA from bran, have significant antioxidant and free radical scavenging activities. These could be potentially used as important sources of natural antioxidants. Significance and novelty This finding encourages the exploration of sorghum by-products (bran and spent grain) in the production of natural phenolic antioxidants for functional food preparations.