BACTERIOCINS, GROWTH-INHIBITORY SUBSTANCE S, OF LACTIC-ACID BACTERIA

Lactic acid bacteria have been traditionally used for the fermentation of foods and beverages because of their contribution to flavor and ar oma development and to spoilage retardation. The preservative effect o f lactic acid bacteria during the manufacture and subsequent storage o f fermented foods is mainly due to the acidic conditions that they cre ate in converting carbohydrates to organic acids (lactic acid and acet ic acid) in the food during their development. Recently, it has become clear that lactic acid bacteria can produce and excrete inhibitory su bstances, such as hydrogen peroxide, diacetyl, and bacteriocins, in ad dition to organic acids. Bacteriocins can be biologically active prote ins or protein complexes displaying a bactericidal mode of action towa rds Gram-positive bacteria, and particularly towards closely related s pecies. Because bacteriocins are degraded and inactivated in the human alimentary canal and lactic acid bacteria have been used in foods sin ce ancient times, bacteriocins are used as natural food preservatives. As such, they have been the subject of a considerable amount of resea rch. We outline here recent studies on bacteriocins, mainly nisin prod uced by Lactococcus lactis subsp. lactis.