High-yield purification of commercial lactulose syrup

Abstract A simple process for purifying lactulose in commercial lactulose syrups was developed. The objective was to establish a selective enzymatic hydrolysis of lactose and epilactose and further removal of monosaccharides by activated charcoal and water/ethanol solutions. Four commercial β-galactosidases from different microorganisms were tested obtaining significant differences in their activities towards the three disaccharides present in the lactulose syrup. β-galactosidases from Bacillus circulans (Biolactasa® NTL*2) and Bifidobacterium bifidum (Saphera® 2600 L) showed a reduced enzymatic activity towards lactulose and a high enzymatic activity towards lactose. These two enzymes were chosen to optimize the lactose hydrolysis methodology using Response Surface Methodology (RSM). Once chosen the optimum enzymatic conditions to selectively hydrolyse lactose present in the lactulose syrup, the hydrolysed sample was treated with activated charcoal and water/ethanol solutions to eliminate all monosaccharides. The proposed method offers a product with high purity (>94%) and high recovery (>80%) of lactulose.