Up to date, the molecular mechanisms allowing the growth of L. rhamnosus in cheese are still poorly understood. NSLAB development during ripening can be attributed to their ability to use the major nutrient sources available in ripened cheese, that is lactose-free. The nutrient sources available include milk components modified by technological treatment check details (rennet addition and curd cooking) and starter LAB development, starter LAB metabolites and cell lysis products. Potential substrate for microbial growth are represented

by small peptides or amino acids [4], citrate, lactate, and free fatty acids [12]. Additionally, sugars and phospholipids, nucleic acids and peptides can be released in the cheese matrix when SLAB autolysis starts to occur [13–15]. These compounds represent selleck chemical carbon sources that could yield intracellular pyruvate

(i.e. through metabolism of citrate, lactate, amino acids, and nucleotides) or be converted into different metabolites. To investigate the metabolic pathways occurring in L. rhamnosus during cheese ripening, Bove and colleagues [16] recently compared the proteomic profiles of 10 L. rhamnosus strains grown in MRS and a cheese-like medium (Cheese Broth, CB). Differently from MRS, which is the standard laboratory medium for lactobacilli [17] and is considered to be a rich substrate with glucose as the primary carbon source for microbial growth, CB is an experimental medium formulated with 20-month-ripened PR cheese [10, 16, 18], that tries to mimic the nutritional composition of PR cheese during ripening. PR cheese, and thus CB, is considered to be a substrate poor in carbohydrates and characterized selleckchem by the absence of milk sugar, lactose. During the curd acidification step of PR cheese production, the conversion of lactose into lactic acid is the main biochemical process that occurs. Lactose is completely depleted within 24 to 48 h [12]. The composition of CB, prepared as the protocol of Neviani et al. [10], is the following

(g/l): proteins, 80.92; lactose, 0.00; glucose, 0.00; galactose, 0.00; lactic acid, 3.82; NaCl, 3.4; sodium citrate, 20.64. According to the findings of Bove et al. [16] compared to the cultivation in MRS, the differentially expressed proteins under cheese-like conditions were mainly linked to protein biosynthesis and catabolism, nucleotide and carbohydrate metabolisms, citrate metabolism, cell Montelukast Sodium wall and exopolysaccharide biosynthesis, cell regulation, oxidation/reduction processes, and stress response [16]. Notably, L. rhamnosus produced lactic acid as the primary end product when growing in MRS, whereas in CB low levels of lactic acid together with high levels of acetic acid were detected for all strains. Despite this common trend, the authors also observed strain-specific physiological responses, suggesting a strain variability in the adaptation to changing environmental conditions in accordance with genetic polymorphism studies [11]. Among all strains, L.