The thermostable 4,6-α-glucanotransferase of Bacillus coagulans DSM 1 synthesizes isomaltooligosaccharides

The 4,6-α-glucanotransferases of the glycoside hydrolase family 70 can convert starch into isomalto-oligosaccharides (IMOs). However, no thermostable 4,6-α-glucanotransferases have been reported to date, limiting their applicability in the starch conversion industry. Here we report the identification and characterization of a thermostable 4,6-α-glucanotransferase from Bacillus coagulans DSM 1. The gene was cloned and the recombinant protein, called BcGtfC, was produced in Escherichia coli. BcGtfC is stable up to 66 °C in the presence of substrate. It converts debranched starch into an IMO product with a high percentage of α-1,6-glycosidic linkages and a relatively high molecular weight compared to commercially available IMOs. Importantly, the product is only partly and very slowly digested by rat intestine powder, suggesting that the IMO will provide a low glycaemic response in vivo when applied as food ingredient. Thus, BcGtfC is a thermostable 4,6-α-glucanotransferase suitable for the industrial production of slowly digestible IMOs from starch.