Selective production of rubusoside from stevioside by using the sophorose activity of β-glucosidase from Streptomyces sp. GXT6.

In order to produce rubusoside, enzymes with preferential specificity for the saccharide sophorose were tested for ability to produce rubusoside from stevioside. We identified BGL1, a β-glucosidase from Streptomyces sp. GXT6, as an enzyme for rubusoside production. Out of several saccharide substrates, BGL1 showed the most affinity to sophorose. This enzyme only hydrolyzes the glucose moiety of the sophoroside at C-13 in stevioside. Production of rubusoside was determined by (1)H and (13)C nuclear magnetic resonance (NMR). Thus, rubusoside was produced from stevioside and the stevioside conversion rate was 98.2 %. The production yield of rubusoside was 78.8 % in 6 h.