Effect of the addition of amino acids in relation to the growth of the strain of Lactobacillus plantarum in natural orange juice.

PERÉZ MB, SAGUIR FM Y MANCA DE NADRA MC

Rosario, Argentina

Congreso; V CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL. SAMIGE.; 2008

Sociedad Argentina de Microbiología General

In a previous study we demonstrated the amino acids requirements of the strains of Lactobacillus plantarum N4 and N8 isolated from oranges. Six common amino acids were necessary for growth of both strains. The N4 strain other two amino acids required in addition to the six amino acids necessary for growth. The objective of this study was to evaluate the growth parameters of Lactobacillus plantarum N4 and N8 from oranges from Tucumán, Argentina, in orange juice and in the same medium added with the sulphur amino acids methionine (non-essential) and cysteine (essential) and the aromatic amino acid phenylalanine (stimulatory). The physical and chemical changes produced in the natural media due to microbial growth were evaluated. Natural orange juice was clarified and autoclaved at 1 atm of overpressure. Amino acids were individually added at 0.2, 0.5 and 1g/l. Bacterial cultures were inoculated at a rate of 2%, and incubated at 30°C for 24 h. Bacterial growth was determined by counting cfu/ml. In samples of culture supernatants residual glucose was determined during growth in the different conditions. Lactobacillus plantarum N4 and N8 developed in natural medium with a growth rate of 0,30 and 0.36 h -1 reaching a final cell concentration of 8,6 x10 8 and 3.2x10 8 cfu/ml, respectively. No change in growth parameters of the strain N4 was observed by the addition of cysteine, methionine or phenylalanine to the natural medium. In presence of 0.5 and 1g/l of cysteine the N8 strain growth rate diminished to 0.15 and 0.14 h -1, respectively. By contrast, 0.2g/l of cysteine increased its growth rate, reaching the maximum cell concentration at 14 h of incubation. Methionine enhanced the growth parameters of the N8 strain in all assayed concentrations. In presence of 1 g/l, the maximum final biomass (4.52x10 8 cfu/ml) and growth rate (0.42 h -1) were reached. Phenylalanine also stimulated the N8 strain growth rate, especially when concentrations of 0.5 and 1 g/l were present. In these conditions the final biomass also increased. Initial glucose consumption was about of 11.8 % for the N4 strain and about of 14 % for the N8 strain, except in the medium with phenylalanine where it corresponded to 25%. The initial pH diminution during growth in the different assayed media was correlated with the N4 and N8 strains fermentative metabolisms. Considering the growth responses in the natural medium and added with amino acids, it possible to infer that the nitrogen composition of orange juice could be enough to satisfy the Lactobacillus plantarum N4 amino acids requirements, independently of their categories as essential, non-essential or stimulatory amino acid. However, the Lactobacillus plantarum N8 growth was more effective in the natural medium with amino acids, principally methionine or phenylalanine than without them.