Acid modification of starch granules in alcohols: effects of temperature, acid concentration, and starch concentration

The acid modifications of potato, amylomaize-7, and waxy maize starches were conducted in methanol, ethanol, 2-propanol, and 1-butanol using a wide range of acid concentrations (0.36 to 5.0%, w/v) and temperatures of 5 to 65 °C. It was found that limiting degrees of polymerization (dp) values were obtained in 72 h of reaction. The resulting products were modified starch granules that contained new types of limit dextrins. It also was found that the dp values of the limit dextrins were dependent on the concentration of the starch in the alcohol suspension. At a constant concentration of acid, the degree of hydrolysis was inversely proportional to the concentration of the starch suspended in the alcohol. This is explained as due to a decrease in the concentration of acid inside the starch granules as the number of starch granules are increased. We further explore the scope of preparing modified starches with different limiting dp values by studying the reaction of potato starch in the four alcohols with 0.36 to 5% w/v HCl at different temperatures from 5 to 65 °C in 10°C intervals. The study shows that by the selection of the alcohol, the acid concentration, the temperature, and the starch concentration, a wide range of limit dextrins, with selected dp values, can be produced.