Enzymatic Glucosylation of Salidroside from Starch by α-Amylase

alpha-Amylases are among the most important and widely used industrial enzymes for starch processing. In this work, an alpha-amylase from Bacillus subtilis XL8 was purified and found to possess both hydrolysis and transglycosylation activities. The optimal pH and temperature for starch hydrolysis were pH 5.0 and 70 degrees C, respectively. The enzyme could degrade soluble starch into beneficial malto-oligosaccharides ranging from dimer to hexamer. More importantly, it was able to catalyze alpha-glycosyl transfer from the soluble starch to salidroside, a medicinal plant-derived component with broad pharmacological properties. The transglycosylation reaction catalyzed by the enzyme generated six derivatives in a total high yield of 73.4% when incubating with 100 mg/mL soluble starch and 50 mM salidroside (pH 7.5) at 50 degrees C for 2 h. These derivatives were identified as alpha-1,4-glucosyl, maltosyl, maltotriosyl, maltotetraosyl, maltopentaosyl, and maltohexaosyl salidrosides, respectively. They were novel promising compounds that might integrate the bioactive functions of malto-oligosaccharides and salidroside.