Highly efficient synthesis of ethyl hexanoate catalyzed by CALB-displaying Saccharomyces cerevisiae whole-cells in non-aqueous phase

A recombinant Saccharomyces cerevisiae displaying Candida antarctica lipase B (CALB) on the cell surface was constructed and used as a whole-cell biocatalyst to catalyze the esterification of hexanoic acid and ethanol for the preparation of ethyl hexanoate, a fragrance compound of liquor. Various reaction parameters affecting the esterification catalyzed by CALB-displaying S. cerevisiae whole-cells were investigated. The optimal reaction conditions were reaction temperature 40 °C, hexanoic acid concentration 0.2 M, the ratio of hexanoic acid to ethanol 1:1.25 and the amount of cells 60 g/l (17 U/g-dry cell). Molecular sieves (3 Å) were added to the reaction medium as the water absorbent. The yield reached 98.2% after reaction for 12 h under the optimal conditions. The CALB-displaying S. cerevisiae whole-cell biocatalyst exhibited quite a good operational stability in the esterification, and more than 95% of its original activity was retained after 10 batches reaction. Thus, CALB-displaying S. cerevisiae whole-cell biocatalyst is promising for esters synthesis in non-aqueous phase.