Production of isomalto-oligosaccharides by cell bound α-glucosidase of Microbacterium sp.

Isomalto-oligosaccharides (IMOs), one of the emerging prebiotics, were synthesized by transglycosylation activity of the cell bound α-glucosidase of a novel strain of Microbacterium sp. using maltose as a glycosyl donor. Parameters affecting yield were optimized and a yield of 85 g/l was obtained at 40% (w/v) initial substrate concentration after 24 h using whole cells (∼25 IU α-glucosidase activity). A mixture of isomaltotriose, isomaltotetraose, isomaltopentaose and isomaltohexaose were obtained as determined by electrospray ionization mass spectrometry. Addition of 0.5 M LiCl to the reaction mixture lead to a further 15% increase in the yield. The synthesized IMOs were purified for structure analysis by preparative thin layer chromatography and structures elucidated by 1H and 13C NMR. The chemical shift values of 13C NMR clearly confirmed that the products formed were isomaltotriose and isomaltotetraose (α-1,6 linked). The reactions were scaled up in a column to 100 ml level using immobilized cells. An increase in productivity by 4.2 times was achieved in this system with a conversion efficiency of 24%.