Free sugars and non-starch polysaccharides–phenolic acid complexes from bran, spent grain and sorghum seeds

Abstract

Free sugars and non-starch polysaccharide-phenolic acid complexes were isolated from sorghum seeds and their major by-products namely bran and spent grain. Total sugar (12.56%) and reducing sugar (10.47%) in free sugars were highest in spent grain. The major soluble sugars identified in materials were maltose, glucose, sucrose, fructose, and raffinose. Hemicelluloses B (2.95–10.82%) and calcium hydroxide extractable polysaccharides (CHEP) (2.20–5.22%) were obtained with the highest yields. The CHEP fractions were completely water-soluble. The major sugars identified in non-starch polysaccharides (NSP) fractions were arabinose, xylose, galactose, and glucose. The Pentose/Hexose ratio was highest in CHEP, in spent grain, it was fourteen-fold that of bran. Ferulic, coumaric and p-hydroxybenzoic acids were present in all the NSP and absent in the alkali-insoluble residues, ferulic acid (56.31–100.73 mg/100 g sample) being the major phenolic acid present. Ferulic, coumaric and vanillic acids were identified as the major phenolic acids in CHEP fractions. Based on their solubility, pentose and phenolic acid contents, NSP from sorghum by-products especially CHEP could exhibit high functional properties when added to foods.