Genetic, enzymatic and metabolite profiling of the Lactobacillus casei group reveals strain biodiversity and potential applications for flavour diversification.

The Lactobacillus casei group represents a widely explored group of lactic acid bacteria, characterized by a high level of biodiversity. In this study, the genetic and phenotypic diversity of a collection of more than 300 isolates of the Lact. casei group and their potential to produce volatile metabolites important for flavour development in dairy products, was examined. Following confirmation of species by 16S rRNA PCR, the diversity of the isolates was determined by pulsed-field gel electrophoresis. The activities of enzymes involved in the proteolytic cascade were assessed and significant differences among the strains were observed. Ten strains were chosen based on the results of their enzymes activities and they were analysed for their ability to produce volatiles in media with increased concentrations of a representative aromatic, branched chain and sulphur amino acid. Volatiles were assessed using gas chromatography coupled with mass spectrometry. Strain-dependent differences in the range and type of volatiles produced were evident. Strains of the Lact. casei group are characterized by genetic and metabolic diversity which supports variability in volatile production. This study provides a screening approach for the knowledge-based selection of strains potentially enabling flavour diversification in fermented dairy products.