Enzymatic production of lactulose

Lactulose has received much attention in recent years because of its therapeutic and health-promoting properties, being considered as one of the most valuable compounds derived from lactose. Lactulose has been used for decades as a medicine in the treatment of chronic constipation and hepatic encephalopathy, but its prebiotic condition has opened also a field for it in the functional food business. Lactulose is produced by chemical synthesis with alkaline catalysts. Being a poorly specific reaction, pure lactose is needed as raw material and complex downstream operations are required, waste disposal being also an issue. The synthesis of lactulose by enzyme catalysis appears as an interesting technological option to overcome the limitations inherent to chemical synthesis but to date no enzymatic process is competitive. Two enzyme strategies have been proposed considering β-galactosidase transgalactosylation of fructose with lactose and lactose epimerization with cellobiose 2-epimerase. The former has the drawback of producing lactulose galacto-oligosaccharide mixtures, so it is not an option if pure lactulose is the required product; the latter is a more attractive and straightforward strategy, but the enzyme is produced in a non-generally recognized as safe organism and apparently is not yet available commercially. The chapter also reviews current and potential applications of lactulose.