Study on the mechanism of ultrasound-accelerated enzymatic hydrolysis of starch: Analysis of ultrasound effect on different objects

Enzymatic hydrolysis of starch is an important process in the food industry. In the present work, ultrasound was introduced in glucoamylase pretreatment, starch pretreatment and mixed reaction system treatment to enhance starch hydrolysis efficiency. These different processes were studied to explore the mechanism of ultrasound in promoting enzymatic reactions. The hydrolysis degree of starch was determined via measuring the reducing sugar yield. Ultrasound caused enzyme inactivation under high temperatures, high ultrasonic power and long-time treatment, especially at high temperatures exceeding 65 °C. Ultrasound pretreatment of starch before enzymolysis led to the furtherance of starch hydrolysis degree. Meanwhile, sonicating the mixed enzymatic reaction system below 65 °C promoted starch hydrolysis significantly, inducing more than five- fold growth in the degree of starch hydrolysis as much as the ultrasound pretreatment caused. Molecular weights analysis conducted by the MALLS system reflected the enormous damage of starch molecules caused by ultrasound. The amylose contents and chain length distributions of samples were separately analyzed by iodine binding method and size exclusion chromatography. The results of the two experiments illustrate that ultrasound could promote the enzymatic hydrolysis of amylopectin, which is harder for glucoamylase to hydrolyze compared to amylose.