Non-starter lactic acid bacteria.

In cultured dairy products, non-starter lactic acid bacteria (NSLAB) are only important in ripening and ripened cheeses. They mainly comprise facultatively homofermentative lactobacilli, e.g., Lactobacillus casei, Lb. paracasei. Lb. curvatus and Lb. plantarum, although pediococci and enterococci are found in lower numbers in some cheeses. Some obligate heterofermentative species, e.g.. Lb. brevis are occasionally found. During ripening the NSLAB grow from low numbers of c. 102to 108 cfu/g over several weeks or months depending on the cheese and its ripening temperature. NSLAB require an energy source for growth but lactose has been metabolised completely to lactate by the time exponential growth of NSLAB occurs. Citrate, arginine, sugars in lysed starter cells and in the milk fat globule membrane have been suggested as energy sources in cheese. The chromosome of at least one strain has been completely sequenced. Generally it is believed that their source is post pasteurisation contamination from equipment and air. However, many strains resist pasteurisation implying that raw milk is also a major source. The effect of NSLAB on cheese flavour has been studied for over 120 years with variable results. More recent studies have generally shown a positive effect of selected strains on cheese flavour formation. During ripening, they are responsible for converting L lactate to D lactate and cause development of white spots on aged Cheddar cheese due to calcium-D-lactate formation. Many NSLAB metabolise citrate to formate and acetoin; they also metabolise and amino acids, especially methionine to potent S containing flavour compounds like niethanethiol and its degradation compounds, as well as various S containing esters. These and other aspects of NSLAB will be discussed in the presentation. [ABSTRACT FROM AUTHOR]