Efficient synthesis of enantiomeric ethyl lactate by Candida antarctica lipase B (CALB)-displaying yeasts.

The whole-cell biocatalyst displaying Candida antarctica lipase B (CALB) on the yeast cell surface with alpha-agglutinin as the anchor protein was easy to handle and possessed high stability. The lyophilized CALB-displaying yeasts showed their original hydrolytic activity and were applied to an ester synthesis using ethanol and L: -lactic acid as substrates. In water-saturated heptane, CALB-displaying yeasts catalyzed ethyl lactate synthesis. The synthesis efficiency increased depending on temperature and reached approximately 74% at 50 degrees C. The amount of L: -ethyl lactate increased gradually. L: -Ethyl lactate synthesis stopped at 200 h and restarted after adding of L: -lactic acid at 253 h. It indicated that CALB-displaying yeasts retained their synthetic activity under such reaction conditions. In addition, CALB-displaying yeasts were able to recognize L: -lactic acid and D: -lactic acid as substrates. L: -Ethyl lactate was prepared from L: -lactic acid and D: -ethyl lactate was prepared from D: -lactic acid using the same CALB-displaying whole-cell biocatalyst. These findings suggest that CALB-displaying yeasts can supply the enantiomeric lactic esters for preparation of useful and improved biopolymers of lactic acid.