Abstract
Production of 1-lactulose and lactulose using commercial β-galactosidase DSM Maxilact® 5000 in the presence of fructose was investigated. Experiments were performed at 40°C and pH 7.5. Lactose starting concentration was constantly 250g/l. A novel transgalactosylation product 1-lactulose was detected besides lactulose. Effects of fructose concentration, reaction time and enzyme concentration on transgalactosylation reactions were discussed. In all reactions, the yield ratio 1-lactulose:lactulose was close to 3:1 due to the regioselectivity of β-galactosidase. The maximum production of 1-lactulose and lactulose was approximately 22 and 8g/l, respectively, when fructose concentration was increased to 100g/l. Lactose hydrolysis was significantly retarded since fructose strongly attracted water molecules. Higher enzyme concentration can accelerate transgalactosylation reactions without affecting the maximum production of transgalactosylation products. Fructose was a more preferred galactosyl acceptor than lactose, since the synthesis of galactooligosacchairdes was found to be absolutely inhibited in the presence of fructose.
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