L. plantarum is auxotrophic for L-tyrosine , and indeed L. plantarum IR BL0076 could not grow in the synthetic medium used in this study without the inclusion of tyrosine. Therefore, the synthetic peptides in medium
2 were presumably metabolized even during the early stages of culture to release tyrosine and to allow the growth. This is consistent with the demonstration that two Lactobacillus strains (Lactobacillus homohiochii and Lactobacillus curvatus) isolated from sausages, express tyrosine and ornithine decarboxylase activities allowing growth at early stages of culture ; both strains display extracellular proteolytic activity which reaches a maximum in the early exponential growth. This activity is higher when the cells Compound Library cost were grown in a peptide-rich medium. However, peptide transport and a subsequent intracellular hydrolysis is also compound screening assay plausible. Although LAB proteinases have a broad specificity and release oligopeptides in the range of 4 to 8 AA, intracellular peptidases are required for the complete degradation of peptides . Figure 2 Influence of tyrosine or tyrosine containing peptides on growth and tyramine production by Lactobacillus plantarum IR BL0076. Lactobacillus plantarum IR BL0076 was grown in MRS medium (control curve; dashed line), synthetic medium with free tyrosine (continuous line) or in medium containing synthetic peptides as the sole
tyrosine sources (dotted line). Tyramine was assayed by HPLC after various times of growth of L. plantarum IR BL0076 (OD600nm = 1.0; 1.6; 1.8), in both culture media. Each value is the mean ± SD of three independent selleck products experiments. Tyramine production by lactobacillus plantarum IR BL0076 Supernatant harvested from the cultures after various times of growth was analyzed by HPLC to determine tyramine production (Figure 2). From Gomez-Alonso et al. , the detection limit for aminoenone derivative of tyramine is 0.02 mg.L-1. Tyramine was identified by HPLC-MS (Table 1). At culture OD600nm = 0.2, L-gulonolactone oxidase no tyramine was detected in any culture. Tyramine was detected, at similar concentrations, in cultures
in both media from OD600nm = 1.0. Concentrations of tyramine for both media were measured between 1.6 and 5.1 mg.L-1 (minimal and maximal measures respectively). The concentrations measured in both media are usually found in wine. Indeed in red wines, tyramine concentration can reached 28 mg.L-1 which is the upper limit, but most of time these concentrations are lower than 2.5 mg.L-1. Therefore, L. plantarum was able to synthesize tyramine similarly from free tyrosine and from peptides containing tyrosine. Table 1 Identification of tyrosine and tyramine by HPLC-MS Amine Derivated mass Molecular ion Caracteristic ions Tyramine 307 306 306,260,214,186 Tyrosine 351 350 350, 306, 260 Tyramine was produced throughout growth and it accumulated as the biomass increased.