Bioconversion of L malic acid into L lactic acid using a high compacting multiphasic reactor (HCMR)

Biotransformation of L malic acid into L lactic acid was studied in a fluidised bed reactor using cells of Lactobacillus sp. 89 and Leuconostoc oenos ATCC 23278 immobilised in a calcium alginate matrix. The reactor was used in a batch or a continuous manner under a non‐oxidising atmosphere. It was shown that 3 mm diameter beads loaded with 6 and 30 mg dry matter per gram of gel were the best operating conditions for Leuconostoc and Lactobacillus respectively. The optimal working conditions were as follows: pH = 3.0–5.0, temperature = 30°C for Lactobacillus and pH = 3.0, temperature = 25°C for Leuconostoc. No inhibition due to lactic acid was observed and the internal diffusional effects were negligible. The short catalyst life that was initially observed with both strains resulted from a depletion in NAD and Mn 2+ , two basic cofactors for malolactic enzymes. To prevent this detrimental effect, a regeneration process for biocatalyst was proposed.