Characterization of a novel cellobiose 2-epimerase from thermophilic Caldicellulosiruptor obsidiansis for lactulose production

Publication Type

Journal contribution (peer reviewed)

Authors

Chen, Q.; Levin, R.; Zhang, W.; Zhang, T.; Jiang, B.; Stressler, T.; Fischer, L.; Mu, W.

Year of publication

2016

Published in

Journal of the Science of Food and Agriculture

DOI

10.1002/jsfa.8148

BACKGROUND: Lactulose, a bioactive lactose derivative, has been widely used in food and pharmaceutical industries. Isomerization of lactose to lactulose by cellobiose 2-epimerase (CE) has recently attracted increasing attention, since CE produces lactulose with high yield from lactose as a single substrate. In this study, a new lactulose-producing CE from Caldicellulosiruptor obsidiansis was extensively characterized.

RESULTS: The recombinant enzyme exhibited maximal activity at pH 7.5 and 70 °C. It displayed high thermostability with T_m of 86.7 °C. The half-life was calculated to be 8.1, 2.8, and 0.6 h at 75, 80, and 85 °C, respectively. When lactose was used as substrate, epilactose was rapidly produced in a short period, and afterwards both epilactose and lactose were steadily isomerized to lactulose, with a final ratio of 35: 11: 54 for lactose: epilactose: lactulose. When the reverse reaction was investigated using lactulose as substrate, both lactose and epilactose appeared to be steadily produced from the start.

CONCLUSION: The recombinant CE showed both epimerization and isomerization activities against lactose, making it an alternative promising biocatalyst candidate for lactulose production.