Evaluation of the Amino Acid Composition and Content of Organic Acids of Complex Postbiotic Substances Obtained on the Basis of Metabolites of Probiotic Bacteria Lacticaseibacillus paracasei ABK and Lactobacillus helveticus H9

In this article, the probiotic strains of Lacticaseibacillus paracasei ABK and Lactobacillus helveticus H9 were cultured in reconstituted skim milk (RSM medium) and MRS broth, and the cell biomass was removed at the end of fermentation in order to obtain postbiotic substances. In postbiotics, the composition of total amino acids, and also the content of free amino acids and organic acids were analyzed. It was shown that in all RSM-based postbiotic substances the concentration of all free amino acids increased. On the contrary, in the MRS-based postbiotics free amino acids were mostly consumed during fermentation; however, a substantial, two-fold, decrease in methionine concentration was observed in postbiotics obtained with L. paracasei ABK. Both L. paracasei ABK and L. helveticus H9 strains showed change in their fermentation profile from homofermentative in MRS broth to mix-acid fermentation in RSM medium. Both strains produced lactic acid in the investigated media and produced lactate together with acetate in RSM. L. helveticus H9 additionally synthesizes succinic acid on both media. Thus, it has been shown that RSM is more preferable than MRS for fermentation with L. paracasei ABK and L. helveticus H9 for obtaining postbiotics enriched with free amino acids and organic acids.