Lactic acid bacteria as starter cultures: An update in their metabolism and genetics

Lactic acid bacteria (LAB) are members of an heterogenous group of bacteria which plays a significant role in a variety of fermentation processes. The general description of the bacteria included in the group is gram-positive, non-sporing, non-respiring cocci or rods. An overview of the genetics of lactococci, Streptococcus thermophilus, lactobacilli, pediococci, leuconostocs, enterococci and oenococciis presented with special reference to their metabolic traits. The three main pathways in which LAB are involved in the manufacture of fermented foods and the development of their flavour, are (a) glycolysis (fermentation of sugars), (b) lipolysis (degradation of fat) and (c) proteolysis (degradation of proteins). Although the major metabolic action is the production of lactic acid from the fermentation of carbohydrates, that is, the acidification of the food, LAB are involved in the production of many beneficial compounds such as organic acids, polyols, exopolysaccharides and antimicrobial compounds, and thus have a great number of applications in the food industry (i.e. starter cultures). With the advances in the genetics, molecular biology, physiology, and biochemistry and the reveal and publication of the complete genome sequence of a great number of LAB, new insights and applications for these bacteria have appeared and a variety of commercial starter, functional, bio-protective and probiotic cultures with desirable properties have marketed.