Improvement of functional properties of a thermostable ?-glycosidase for milk lactose hydrolysis

In this work, a new exploitation of the thermostable ?-glycosidase from Sulfolobus solfataricus expressed in Saccharomyces cerevisiae to create functional foods for low lactose diets was evaluated. For this purpose, the lactose hydrolysis reaction using immobilized and soluble enzymes was investigated. Activity and stability at different conditions of pH and temperature were tested. The immobilization process had a big impact on the catalysis performance, leading to an enhancement of the enzymatic reaction rate on lactose, as demonstrated by the increasing of 2 and 2.5 folds of Kcat and Kcat/KM, respectively. Moreover, the maximal activity for the immobilized form was referred at pH 6.5 instead of 7.0, leading to an improvement of the catalytic performance at milk pHs. Although the soluble enzyme was already weakly inhibited by the reaction products, the immobilization further reduced the inhibitory action of glucose increasing the Ki from 96.7 to 110.4 mM. Finally, the immobilized enzyme showed high hydrolysis rate in whole milk that yielded 99% of lactose breakdown in 10 and 30 min at 60 and 40°C, respectively. These results support the application of the immobilized ?-glycosidase for the development of new functional foods particularly suitable to the alleviation of lactose intolerance.