Various functional oligosaccharides, such as lactulose, galacto-oligosaccharides (GOS) 72 , cyclodextrins or oligodextran (5-8 kDA) , are known to have potential applications in the fine chemicals and pharmaceutical industries. β-galactosidase can catalyze the direct obtention of GOS (Figure ) and lactulose from lactose via transgalactosylation reactions . Lactose (a disaccharide composed of glucose and galactose) is generated in high contents in the dairy by-product of many (bio)chemical processes 78 , and acts as a renewable feedstock to produce such building blocks.