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.