Enzymatic production of l-menthol by a high substrate concentration tolerable esterase from newly isolated Bacillus subtilis ECU0554

Article abstract of DOI:10.1002/adsc.200800412

Enzymatic preparation of l-menthol has been attracting much attention in the flavor and fragrance industry. A new ideal strain, Bacillus subtilis ECU0554, which exhibited high hydrolytic activity and excellent enantioselectivity towards l-menthyl ester, has been successfully isolated from soil samples through enrichment culture and identified as Bacillus subtilis by 16S rDNA gene sequencing. The esterase extracted from B. subtilis ECU0554 (BSE) showed the best catalytic properties (E > 200) for dl-menthyl acetate among the five menthyl esters examined. Enantioselective hydrolysis of 100 mM dl-menthyl acetate at 30°C and pH 7.0, using crude BSE as biocatalyst and 10% ethanol (v/v) as cosolvent, resulted in 49.0% conversion (3 h) and 98.0% ee for the l-menthol produced, which were much better than those using commercial enzymes tested. Moreover, BSE exhibited strong tolerance against high substrate concentration (up to 500 mM), and the concentration of l-menthol produced could reach as high as 182 mM, and more importantly, the optical purity of l-menthol produced was kept above 97% ee, which were not found in previous reports. These results imply that BSE is a potentially promising bio-catalyst for the large-scale enzymatic preparation of l-menthol. Using this excellent biocatalyst, the enzymatic production of l-menthol will become a mild, efficient, inexpensive and easy-to-use "green chemistry" methodology.