Physicochemical characterization of enzymatically hydrolyzed heat treated granular starches

Abstract

The effect of heat treatment below gelatinization temperature on the susceptibility of sweet potato and cassava granular starches towards bacterial α-amylase hydrolysis was investigated. Granular starches treated at 60°C showed significantly higher degree of hydrolysis compared to those treated at 45°C, which were 17 and 32% for sweet potato and cassava starches, respectively. SEM showed a smooth granule surface for the native starches. Hydrolyzed heat treated starches at 60°C showed rougher surface and more porous granules compared to those treated at 45°C. The native and hydrolyzed heat treated starches showed no significant difference in their average granule size. Swelling power and syneresis of the starches decreased after hydrolysis. FTIR showed extensive degradation of the starches amorphous structure in hydrolyzed heat treated starches. Native and hydrolyzed heat treated cassava and sweet potato starches showed an A-type XRD pattern with strong peaks at 2θ = 15° and 23° and a dual peak at 17° and 18°. The hydrolyzed heat treated starches showed sharper peaks suggesting that hydrolysis occurred on the amorphous domains. In all, starches treated at 60°C showed higher degree of hydrolysis compared to those treated at 45°C with both exhibiting modified physicochemical characteristics.