Modification of steviol glycosides using α-amylase

Stevia extract usually contains a high content of stevioside which produces a significant bitter aftertaste, thus limiting its commercial application as a high-potency sweetener in foods. In order to improve its organoleptic properties, the stevia extract (containing 90 g/100 g stevioside) was modified by α-amylase from Aspergillus oryzae (TAKA), with soluble starch as substrate. Stevioside was found to be an efficient acceptor substrate and has been transglycosylated during the reaction. The mono-glycosylated stevioside was the major product. The influences of reaction conditions on the conversion yield of stevioside, including pH, reaction temperature, weight ratio of stevioside to starch, substrate and enzyme concentrations, were investigated. With 2 g/100 mL stevioside and 20 g/100 mL soluble starch in 0.05 mol/L potassium phosphate buffer, pH 6.4 and 50 U/mL TAKA, 48.2% conversion yield of stevioside was obtained in 0.5 h at 70 °C. For the enzymatically modified steviol glycosides, the bitter aftertaste was significantly decreased and the sweetness potency was significantly improved.