Abstract

The aim of this research was to investigate essential groups of amino acids and effect of amino acid supplementation. P. acidilactici culture was grown in chemically defined medium (CDM) with initial pH 6.35 and at 30°C. To minimize the number of experiments, the experimental design was based on grouping the metabolic amino acid pool. The selected amino acid groups were the following: a) phenylalanine and tyrosine; b) lysine, methionine, isoleucine; c) leucine and valine and d) histidine. The concentration of each selected amino acid in original CDM was 50 mg/l while its concentration in the modified CDM was reduced to 25 mg/l. Concentrations of biomass, lactic acid, glucose, and selected amino acids were measured. It was found that amount of Ile, Met, and Lys added in CDM-grown P. acidilactici was directly affected lactic acid production rate. Limitation of Phe, Tyr, Leu, Val, and His concentration added had the largest effect on cell growth and lactic acid production. The maximum specific growth rate (µ_max) and the lactic acid production rate obtained from fermentation in modified CDM with 25 mg/l of Phe and Tyr (Run # A) and  Leu  and  Val (Run # C), as compared with fermentation in original CDM, were improved by a factor of 3.4 and a factor of 2.7, respectively. The sub-optimal composition of amino acids in modified CDM was 25 mg/l of Phe, Tyr, Leu and Val at pH 5.5-5.8.

Key words: Lactic acid bacteria, Pediococcus acidilactici, lactic acid, amino acid.