Acetaldehyde Production by Strains Used as Probiotics in Fermented Milk

Lactic acid bacteria have diverse shunts for the metabolism of acetaldehyde, which is involved in the metabolism of carbohydrates, proteins and nucleic acids. In Lactobacillus acidophilus and Lactobacillus casei , strains isolated from feces of healthy children, acetaldehyde can be formed from different sources. Phosphotransacetilase, acetate kinase, aldehyde dehydrogenase and 2-deoxiriboaldolase activities were found in both strains. α-Carboxilase and threonine aldolase activities only occurred in L. acidophilus . In contrast, phosphoketolase activity was present in L. casei , but absent in the other strain studied. The accumulation of acetaldehyde in the growth medium is possible because the enzymes specific activities to form it are higher than those able to convert it to ethanol.