Kinetics, stereospecificity, and expression of the malolactic enzyme

Mass spectrometric measurement of carbon dioxide production was used to stu dy malolactic fermentation (MLF) in Lactobacillus collinoides isolated from cider. The kinetics and stereospecificity of the malolactic enzyme (MLE) w ere studied, and the stoichiometry of the reaction sequence mas investigate d. The optimum pH for activity of the MLE was 4.9. MLF was more rapid (in b oth intact cells and cell extracts) when L-malic acid was used than when D- malic acid or the racemic mixture was added. The enzyme was found to be con stitutively present in L. collinoides. Addition of L-malic acid (37 mM) to the growth medium resulted in increased MLE activity; addition of the D iso mer alone or the racemic mixture resulted in lower activities. Addition of the main sugars in apple juice (fructose, sucrose, and glucose) to the grow th medium in the presence of malic acid repressed production of MLE to simi lar extents in all three cases; in the absence of melic acid, instead of in hibiting MLF, addition of sugars to the growth medium somewhat increased th e residual MLE activity.