Acid modified starch refers to the modified starch treated with acid. It is a kind of soluble starch, which still retains the granular state of starch after dissolution. The solution has good transparency and fluidity, so it is also called soluble modified starch. Starch depolymerization will occur in the process of acid treatment of starch. In order to control the degree of depolymerization, under the premise of controlling the acid addition, the treatment temperature generally does not exceed the gelatinization temperature. Under the action of protons, the glycoside bond breaks, accompanied by the emergence of low molecular weight polymer fragments. The amount of acid depends on the desired conversion degree. In the reaction process, amylopectin is partially degraded first, and then protons attack amylose. The hydrolysis efficiency is high at the initial stage of the reaction. After the starch suspension was modified with acid, the base number, critical absorption value of sodium hydroxide, water holding capacity and gelatinization temperature of the product increased, while the hot paste viscosity, intrinsic viscosity and iodine affinity decreased.
Compared with dextrin, the production technology and product properties of acid modified starch are very different. It is a soluble starch, but still retains the granular state of starch. In fact, the effect of acid on starch molecules has been known for many years. In 1874, Naegeli and Linther prepared acid treated starch respectively. At that time, the starch was treated with 7.5% hydrochloric acid or 15% sulfuric acid at room temperature for 12 days, and the modified starch obtained was heated and boiled at 2% concentration to obtain a completely transparent solution with good fluidity. Therefore, it is usually called soluble modified starch.