Non-starch polysaccharides derived from sorghum grains, bran, spent grain and evaluation of their antioxidant properties with respect to their bound phenolic acids

Sorghum bran (SB) and sorghum spent grain (SSG), the main by-products of sorghum grains (SG) processing, are important sources of dietary fibre (DF). In this research communication, the proximate composition of materials and the antioxidant activities of non-starch polysaccharides (NSP) derived from SB, SSG and SG were evaluated by the reducing power and the scavenging capacities by the DPPH and ABTS radical methods. SSG contained higher amount of proteins (23.85 g/100g), lipids (8.24 g/100g), ash (6.80 g/100g) and total dietary fibre (56.25 g/100g); SB and SSG contained respectively two and three-times more fibres than the SG. Among isolated NSP, the calcium hydroxide extractable polysaccharides (CHEP) were found to be richer in total phenolic contents (580.40–1183.17 Ferulic acid equivalents/g sample) and exhibited the highest antioxidant activities (210.25–249.35 μmol Fe2+E/g sample, 311.35–381.10 μmol TE/g sample and 0.29–0.34 mg/mL for the FRAP, ABTS and DPPH IC50 values, respectively). The study revealed that NSP from sorghum by-products especially the CHEP fractions have significant antioxidant and free radical scavenging activities. These non-starch polysaccharide–phenolic acid complexes from bran and spent grain can be used in various fibre depleted foods while contribute preventing their oxidation. The high antioxidant activity exhibited by NSP isolated from sorghum by-products is mainly due to their high bound phenolic acid contents. This is an added advantage in using these DF as food additives.