Purification and characterisation of a beta-galactosidase from Aspergillusaculeatus with activity towards (modified) exopolysaccharides from Lactococcus lactis subsp cremoris B39 and B891

beta-Galactosidase from Aspergillus aculeatus was purified from a commercia l source for its hydrolytic activity towards (modified) exopolysaccharides (EPSs) produced by Lactococcus lactis subsp. cremoris B39 and B891. The enz yme had a molecular mass of approximately 120 kDa, a pi between 5.3 and 5.7 and was optimally active at pH 5.4 and 55-60 degrees C. Based on the N-ter minal amino acid sequence, the enzyme probably belongs to family 35 of the glycosyl hydrolases. The catalytic mechanism was shown to be retaining and transglycosylation products were demonstrated using lactose as a substrate. The beta-galactosidase was also characterised using its activity towards t wo EPSs having lactosyl side chains attached to different backbone structur es. The enzyme degraded O-deacetylated EPS B891 faster than EPS B39. Furthe rmore, the presence of acetyl groups in EPS B891 slowed down the hydrolysin g rate, but the enzyme was still able to release all terminally linked gala ctose. (C) 2000 Elsevier Science Ltd. All rights reserved.