The dar gene from Lactococcus lactis subsp. cremoris MG1363, encoding the enzyme diacetyl reductase (DAR) was cloned into the expression vector pMG36e under the control of the P32 promoter, and Lc. lactis MG1363 was transformed with this recombinant plasmid by electroporation. Metabolic end products (e. g., pyruvate, lactate, formate, acetoin) of this strain grown in glucose medium were analyzed by HPLC. The overexpression of the plasmid-encoded dar gene in Lc. lactis MG1363 led to the shift from homolactic to mixed acid fermentation and the production of a high level of acetoin, confirming the overexpression of the diacetyl reductase. In addition, the strains overexpressing dar gene and wild type were used as starter cultures in cheese. Different levels of metabolic end products were detected in cheese during the two weeks of ripening compared to the wild type strain.