Impact of Annealing on Susceptibility to Acid Hydrolysis and Physico-Chemical Properties of Cassava Starch

Abstract

Native cassava starch was subjected to modifications by annealing and acid hydrolysis. The effects of annealing on the susceptibility to acid hydrolysis, granular morphology and size distribution, molecular structure and the physico-chemical properties of cassava starch were investigated. The acid hydrolyzed starch granule surface became slightly roughened with a preserved birefringence pattern. Smaller granules were obtained after acid hydrolysis with fragments of granules observed after prolonged hydrolysis for 16 and 32 d. The molecular weight distribution of cassava starch remained unchanged after annealing while degradation of starch components occurred to differing extents after acid hydrolysis. No difference in acid hydrolysis extent was observed between native and annealed cassava starches. Acid hydrolyzed starches possessed significantly lower pasting viscosity than native and annealed starches. In general, the swelling power of cassava starch decreased while solubility increased after longer hydrolysis time. Gelatinization temperatures slightly increased during the first phase of hydrolysis and then decreased accompanied with broader endotherms. A significant increase in gelatinization enthalpy was observed in starch hydrolyzed for 16 and 32 d. The extent of retrogradation of cassava starch increased progressively with decreasing molecular weight of the acid hydrolyzed starches. In addition, the glass transition temperatures of amorphous native and annealed cassava starches at limited moisture were depressed successively with increasing hydrolysis time.