Batch synthesis of galactooligosaccharides from co-products of milk processing using immobilized β-galactosidase from Bacillus circulans

Milk whey (MW) and milk whey permeate (MWP) constitute the main part of co-products derived from milk processing. The use of the transgalactosylation activity of beta-galactosidases is an excellent alternative to add value to these co-products since this is the route for the synthesis of galactooligosaccharides (GOS), a valuable prebiotic sugar. Hereby, we immobilized a beta-galactosidase from Bacillus circulans onto glutaraldehyde-activated chitosan beads. The immobilized enzyme was characterized and the parameters affecting GOS synthesis (pH, temperature, and concentration of MW and MWP) were evaluated. The optimum pH and temperature of activity for the immobilized beta-galactosidase were 50 degrees C and pH 6.0, respectively. The immobilization improves enzyme thermal stability by 2.9 times. In the batch process, the immobilized enzyme exhibited excellent operational stability at 40 degrees C, being able to hydrolyze 91% lactose after 17 cycles of reuse. Regarding GOS synthesis, the immobilized enzyme could be reused for 10 consecutive cycles retaining 74% of the initial activity at 50 degrees C. The maximum concentration of GOS achieved, using MW and MWP, was 159.4 g L-1 and 168.8 g L-1, respectively. Therefore, these results proved that it was possible to obtain, in high concentration, a useful and valuable prebiotic sugar from co-products of milk processing.