Pasting, flow, thermal and molecular properties of maize starch modified with crude phenolic extracts from grape pomace and sorghum bran under alkaline conditions

Abstract

This study determined the effects of phenolic extracts from grape pomace and sorghum bran, reaction time and washing with aqueous ethanol on the pasting, flow, thermal and molecular properties of maize starch. The starch modification was carried out under alkaline conditions. The phenolic extracts increased the peak viscosity of the starch. Reaction time had no significant effect on starch properties. Washing with aqueous ethanol significantly increased the peak, final, and setback viscosities of the phenolic modified maize starches. DSC of phenolic modified starches showed higher enthalpy (ΔH) before and after washing with aqueous ethanol in comparison with starch without phenolic extract. FTIR spectra suggested the possible formation of hydrogen and ether (covalent) bonds between starch and phenolic compounds. It can be concluded that the pasting, flow and thermal properties of maize starch can be modified with phenolic extract under alkaline conditions to produce "clean label" starch-phenolic complex.

Keywords: Grape pomace; Pasting properties; Phenolic extracts; Sorghum bran; Starch-phenolics interactions; Tannin/proanthocyanidins.