STS molecular marker for rapid screening of Lactobacillus casei group as secondary adjunct starter

Flavour perception is very important in the differentiation of fermented dairy products as ripened cheese. Ripened cheese is a dynamic environment involving microbial and biochemical changes which lead to the formation of products characteristics and flavour. The formation of flavours proceeds a rather slowly through several chemical and biochemical reactions during aging. This complex process involves three major metabolic pathways: (1) metabolism of lactate and citrate, (2) liberation of free fatty acids (FFA) and their subsequent metabolism, (3) degradation of the casein matrix of the curd to a range of peptides, followed by degradation to free amino acids (FAA), and ultimately FAA catabolism. These biochemical reactions may be affected by the entire spectrum of cheese microbiota, which is composed of starter LAB (SLAB) and adventitious species including non-starter LAB (NSLAB). NSLAB dominate during ripening thank to their ability to use the major compounds of cheese, such as organic acid (lactic acid produced by SLAB, citric acid of milk), small peptides and FAA, as nutrient sources for grow. The metabolism of NSLAB can lead to the production of different compounds that contribute to the flavour of cheese. Among NSLAB, Lactobacillus casei group participate in cheese aroma formation through reactions which rely on the hydrolytic action of enzymes to lactate, citrate and amino acids. In this research work, L. casei group metabolic capabilities to form flavour compounds were investigated developing STS (sequence tagged site) molecular marker for identification of genes encoding flavour-related enzymes. Lactate and citrate catabolic pathways of the group were considered.