Optimization of lactulose synthesis from whey lactose by immobilized β-galactosidase and glucose isomerase.
In the present study, commercially available whey was used as a lactose source, and immobilized β-galactosidase and glucose isomerase were used to synthesize lactulose from whey lactose in the absence of fructose. Optimal reaction conditions, such as lactose concentration, temperature, ionic strength of the buffer, and ratio of immobilized enzymes, were determined to improve lactulose synthesis using immobilized enzymes. Lactulose synthesis using immobilized enzymes improved markedly after optimizing the reaction conditions. When the lactulose synthesis was carried out at 53.5°C using 20% (w/v) whey lactose, 12U/ml of immobilized β-galactosidase and 60U/ml of immobilized glucose isomerase in 100mM sodium phosphate buffer at pH 7.5, the lactulose concentration and specific productivity were 7.68g/l and 0.32mg/Uh, respectively. Additionally, when the immobilized enzymes were reused for lactulose synthesis, their catalytic activity was 57.1% after 7 repeated uses.
Department of Chemical and Biological Engineering, Korea University, 5 Ga, Anam-dong, Sungbuk-gu, Seoul 136-701, Republic of Korea.
Yoon-Seok
YS
Song
Hee-Uk
HU
Lee
Chulhwan
C
Park
Seung-Wook
SW
Kim
D019747:Aldose-Ketose Isomerases / Q000737:chemistry / Q000378:metabolism*; D004800:Enzymes, Immobilized / Q000737:chemistry / Q000378:metabolism*; D007785:Lactose / Q000378:metabolism*; D007792:Lactulose / Q000378:metabolism*; D001616:beta-Galactosidase / Q000737:chemistry / Q000378:metabolism*
D004800:Enzymes, Immobilized; D007792:Lactulose; D001616:beta-Galactosidase; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase; D007785:Lactose