Synthesis of prebiotic carbohydrates derived from cheese whey permeate by a combined process of isomerisation and transgalactosylation

Background Lactose from cheese whey permeate ( WP ) was efficiently isomerised to lactulose using egg shell, a food‐grade catalyst, and the subsequent transgalactosylation reaction of this mixture with β ‐galactosidase from Bacillus circulans gave rise to a wide array of prebiotic carbohydrates derived from lactose and lactulose.Results Lactulose obtained by efficient isomerisation of WP (16.1% by weight with respect to the initial amount of lactose) showed great resistance to the hydrolytic action of β ‐galactosidase from B. circulans , which preferentially hydrolysed lactose, acting as a galactosyl donor and acceptor. Lactulose had capacity as an acceptor, leading to the formation of lactulose‐derived oligosaccharides. The enzymatic synthesis was optimised by studying reaction conditions such as pH , temperature, time, enzyme concentration and carbohydrate concentration. The maximum formation of galactooligosaccharides with degrees of polymerisation from 2 to 4 was achieved after 5 h of reaction at pH 6.5 and 50 °C with 300 g kg −1 carbohydrates and 3 U mL −1 β ‐galactosidase.Conclusion These findings indicate that the transgalactosylation of isomerised WP with β ‐galactosidase from B. circulans could be a new and efficient method to obtain a mixture with 50% of potentially prebiotic carbohydrates composed of lactulose, and galactooligosaccharides derived from lactose and lactulose.