Biotransformation of stevioside by Leuconostoc citreum SK24.002 alternansucrase acceptor reaction.

Stevioside (13-O-β-sophorosyl-19-O-β-d-glucosyl-steviol) is a non-cariogenic and low-calorigenic diterpenoid glycoside. It has a slightly bitter taste and bad aftertaste. Enzymatic modification by alternansucrase from Leuconostoc citreum SK24.002 was utilised in the biotransformation of stevioside to fully or partially remove the bitter taste of the stevioside. The effect of the reaction conditions including, time (1-24h), temperature (20-40°C), pH (4-7), donor concentration (10-100mg/ml) and enzyme concentration (0.5-2.5U/ml) were investigated in order to maximise the transglucosylation yield. The highest transglucosylation yield of approximately 43.7% was achieved at 20°C, pH 5.4 for 24h using sucrose at 10mg/ml and alternansucrase at 1U/ml. LC/MS analysis confirmed that the product was composed of mono-di- and tri- glucosylated stevioside and their isomers.