Studies on Preparation of β-Galactosidase and Optimization of Reaction Conditions for the Galactooligosaccharides Production

Abstract:

Previously，a recombinant straincontaining the encoding gene of Bacillus circulans β-galactosidase，E.coli BL21 （DE3）/pET-20b-lac，was constructed in our laboratory. In this study，the strain was cultured in shake flask for 24 h，reaching an extracellular enzyme activity of 15 U/mL. The crude enzyme was used for the preparation of oligosaccharides. The reaction conditions，including initial pH，reaction temperature，lactose concentration，enzyme dosage and reaction time，forthe yield of galactooligosaccharides was optimized. The optimal conditions for the conversion was as the following：initial pH 6.5，reaction temperature 55 ℃，initial lactose concentration 700 g/L，enzyme concentration 8 U/mL. When the reaction was performed under this specified conditions，the galactooligosaccharide yield reached the maximum of 57% at 16 h.