Enzymatic synthesis of galacto-oligosaccharides and other lactose derivatives (hetero-oligosaccharides) from lactose

Non-digestible oligosaccharides are applied as functional food ingredients to replace sucrose and to exploit specific biological functions, particularly low cariogenicity, low caloric content, prebiotic activity, and their ability to prevent adhesion of pathogens and toxins to eukaryotic cells. Oligosaccharides derived through enzymatic synthesis from lactose, i.e., galacto-oligosaccharides, lactulose and lactosucrose, account for a major part of the annual oligosaccharide production. Enzymatic production of oligosaccharides employs lactose as galactosyl-donor to transfer the galactosyl-moiety of lactose to suitable acceptor carbohydrates through the activity of β-galactosidases, or employs lactose as a galactosyl-, glucosyl- or fructosyl-acceptor through the activity of β-galactosidases, glucansucrases and fructansucrases. This communication provides an overview on the structural diversity of galacto-oligosaccharides and hetero-oligosaccharides that are produced by enzymatic conversion of lactose, and reviews the strategies used to optimize enzymatic transglycosylation with lactose as glycosyl donor or glycosyl acceptor.