Hydrolysis and antioxidant activity of starch modified with phenolic extracts from grape pomace and sorghum bran under alkaline conditions

The effect of modification with phenolic extracts from grape pomace (GPE) and sorghum bran (SBE) under alkaline conditions for 6 and 12 h, with and without washing with aqueous ethanol (post modification) on the enzymatic hydrolysis as measured by viscosity decrease and antioxidant activity of maize starch was studied. Phenolic-modified starches showed lower rate of starch hydrolysis. The DSC of residues after enzyme hydrolysis showed the conversion of type I inclusion complexes in the unwashed to type II inclusion complexes in the washed phenolic-modified starches. FTIR suggests the presence of covalent bonds in the residues of the phenolic-modified starches due to the retention of starch-bound phenolics. Phenolic-modified starches showed ABTS radical scavenging activity. Ultra-fast liquid chromatography showed polymerisation of monomeric and dimeric procyanidins to oligomeric procyanidins in GPE and SBE-modified starches. It can be concluded that phenolic-modified starches with relatively low hydrolysis and antioxidant activity can be produced under alkaline conditions.

Keywords: FTIR; Proanthocyanidins; Radical scavenging activity; Thermal properties; Viscosity.