Stressful conditions and metabolism of Lactobacillus sakei: impact on the characteristics of fermented products

Lactobacillus sakei is an important food-associated lactic acid bacterium commonly isolated from spontaneously fermented salamis and, it is often used as selected starter cultures in industrial fermented sausage production. L. sakei is highly specialized for a specific ecological niche (meat), where the presence of free amino acids makes the synthesis of these substances superfluous, as demonstrated by its auxotrophy for 18 amino acids. This species exhibits a great ability to colonize salamis from the beginning of production to the end of ripening. Following the carbohydrates’s depletion, the metabolism of L. sakei is redirected to secondary pathways that can affect the texture, nutritional value and aromatic profile. The main activities concern the metabolism of amino acids, sugar products and these metabolic pathways allow gaining energy. These different metabolic features can be exploited to obtain innovative fermented products or to impart well-defined aromatic connotations to traditional ones. This research highlighted the need to improve the use of starter cultures in food industry, in order to guarantee the quality and safety of the final products. The research was focused on different strains of L. sakei to assess their phenotypic and metabolic features, in term of growth performances, amino acids consumption and accumulation of metabolites. Then, one strain was selected to further study its adaptation in relation to the carbon sources added to the growth medium. The use of different analytical approaches (traditional microbiological methods, flow cytometry, HPLC analysis and metabolome analyses by 1H-NMR) allowed to evidence different metabolic and physiological behaviours in relation to the different sugars as active response to harsh conditions. This can be helpful to optimize the use L. sakei as starter culture for the industrial production of fermented sausage, since stressful conditions can affect the microbial technological performances as well as the sensorial features of the final product.