Definition
Lactic acid bacteria (LAB) are a group of Gram positive bacteria that produce lactic acid as the main end product of carbohydrate metabolism. These non sporing organisms are generally non respiring and thrive in nutrient rich environments.
Explanation
Lactic acid bacteria include genera such as Lactobacillus, Lactococcus, Streptococcus, Leuconostoc and Pediococcus. They are facultative anaerobes or microaerophiles that ferment sugars via homofermentative or heterofermentative pathways, yielding lactic acid and, in some species, ethanol or carbon dioxide. LAB tolerate acidic conditions and compete with other microbes by producing organic acids and bacteriocins. They colonize human mucosal surfaces, especially the gastrointestinal and genitourinary tracts, where they contribute to barrier function and immune modulation. In industry, LAB are used to ferment dairy products, vegetables, meat and grains, transforming raw substrates into foods like yogurt, cheese, sauerkraut and sourdough bread. Some species have been developed as probiotics for their ability to survive gastric transit and adhere to epithelial cells. Molecular tools reveal substantial genetic diversity among LAB, which influences flavour, texture, safety and probiotic properties. They are also used in the production of recombinant proteins and as vectors for mucosal vaccines. Although generally regarded as safe, certain streptococcal LAB can be opportunistic pathogens and some strains cause dental caries by acidifying dental plaque.
Fermentation roles and notable points
• Lactococcus lactis is used to ferment milk into cheddar cheese and produces nisin, a bacteriocin used as a food preservative.
• Lactobacillus plantarum aids in the fermentation of vegetables like kimchi and contributes to their tangy flavour.
• Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus cooperate in yogurt starter cultures, converting lactose to lactic acid.
• Leuconostoc mesenteroides initiates sauerkraut fermentation, producing lactic acid and carbon dioxide that create an anaerobic environment.
• Pediococcus pentosaceus is important in cured meat fermentation and the production of sour beers.
Most LAB are safe and have been consumed for centuries. Their metabolic activities preserve foods, develop unique flavours and modulate host microbiota.
Related Terms: fermentation, probiotics, lactic acid, Lactobacillus, Lactococcus