Type and concentration of acid on solubility and molecular size of acid–methanol-treated rice starches differing in amylose content

Abstract

Rice starches differing in amylose content were treated in methanol with acid at 45 °C for 1 h, effects of acid type and concentration on the solubility and molecular size of starch were investigated. Significant differences were found in solubility and weight-average degree of polymerization (DP w) among starches treated with different acids at the equal normality. Starch treated with HCl had lower DP w than treated with H 2SO 4 or HNO 3. The hydrogen-ion concentration in methanol was negatively correlated ( p < 0.001) with the DP w of starch despite of type and concentration of acid used. The increment in degradation extent of waxy rice starch with increasing hydrogen-ion concentration in methanol was lower than that of non-waxy rice starch. Results indicate that the distinct deionization extent of acids in methanol influences the degradation of starch, and that the hydrogen-ion concentration can be used to monitor the degradation of rice starch during acid-treatment in methanol.