Purification of the malolactic enzyme from a Leuconostoc oenos strain and use in a membrane reactor for achieving the malolactic fermentation of wine

Malolactic fermentation is carried out by lactic acid bacteria which convert L-malic acid, present in wine after alcoholic fermentation, into L-lactic acid and CO2 in the presence of NAD(+) and cofactor. Many studies have tried to improve the control and the yield of this conversion with different systems (i,e. selection of strains, stimulating bacteria, hyperproducing modified strains, bioreactors with free or gel-entrapped bacteria, bioreactors with immobilized enzyme), We propose in this paper a membrane reactor with free enzyme and cofactor to carry out malolactic fermentation, First of all we have purified the malolactic enzyme of Leuconostoc anos 84 06 and studied its properties, The specific activity of this malolactic enzyme was increased 7.5-fold from 1.7 units/mg to 12.8 units/mg of protein, An M(r) of 131 000 was determined by gel-filtration chromatography, The apparent K-m vales for L-malic acid, NAD(+) and Mn2+ were respectively 4.2 mM, 18 mu M and 4 mu M for the better purified fraction. Maximum enzymic activity was observed at 35 degrees C and at a pH of 5.5 in 0.05 M phosphate buffer. A reactor was designed in order to obtain a maximal conversion rate as a function of the operating conditions, We can assert that a conversion rate of 70% is reached after 1 week.