Dissimilation of organic acids by dairy lactic acid bacteria

One hundred and eleven different strains of lactic acid bacteria, belonging to the genera Leuconostoc, Streptococcus and Lactobacillus, were examined for their ability to degrade 10 organic acids by detecting CO₂ production, using the conventional Durham tube method. All the strains did not break down succinate, glutarate, 2-oxoglutarate, or mucate. Malate, fumarate, citrate, gluconate, tartrate and pyruvate were variably attacked. A malo-lactic fermentation was brought about by two thirds of S. cremoris and S. lactis strains as well as L. casei but not by L. buchneri or L. brevis. One third of the lactic streptococci examined, i.e. S. cremoris AM₂, ML₈ and SK₁₁ were capable of diacetyl production. They required glucose for cleavage of citrate, whereas Leuconostoc citrovorum and S.faecalis did not. S. cremoris differed from S. lactis in not producing CO₂ from gluconate. From all the lactic acid bacteria examined, only L. plantarum dissimilated tartrate. Production of acetoin and diacetyl is a more reliable evidence for assessing the degradation of pyruvate, compared to detection of evolved CO₂. Facultatively heterofermentative lactobacilli and Leuconostoc citrovorum produced acetoin and diacetyl from pyruvate, whereas the obligately heterofermentative lactobacilli did not, a character that would be of taxonomic value. Glucose fermented by both the facultatively and obligately heterofermentative lactobacilli did not prove to be a metabolic source of acetoin and diacetyl. The facultative heterofermenters degraded pyruvate in the presence of glucose with lactate as the major product together with a mean of acetate of 4.1%, ethanol of 7.9%, acetoin of 1.7% and diacetyl of 2.6% yield on a molar basis after 60 days at 30°C. L. brevis produced acetate and lactate. The role of S. cremoris and the facultatively and obligately heterofermentative lactobacilli in flavour development during the ripening of many cheese varieties has been confirmed.