Addition of glutamine to milk during fermentation by individual strains of lactic acid bacteria and the effects on pyroglutamic and butyric acid

Lactic acid bacteria fermentation generates pyroglutamic and butyric acid, two metabolites that influence the flavour of foods and could significantly benefit human health. In literature, data on the ability of lactic acid bacteria to produce these molecules is limited. Therefore, in this study, single strains were inoculated in milk to determine the quantity of butyric and pyroglutamic acid produced and the effect of glutamine enrichment substrate was evaluated. In addition to Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, which are used in traditional yoghurt, other strains (including some probiotics) isolated from different sources were studied. L. bulgaricus E1 and the probiotic L. casei ATCC393 generated the most butyric acid (110 and 108 mg 100 g-1 d.m., respectively) in media without glutamine. The highest quantity of pyroglutamic acid was produced by Lactobacillus delbruekii subsp. bulgaricus MY (700 mg 100 g-1 d.m.) and the probiotic Lacticaseibacillus casei Shirota (1786 mg 100 g-1 d.m.), respectively. Most of the inoculated strains produced a greater quantity of pyroglutamic acid in the substrate with glutamine. These results are an interesting starting point for researchers to utilize selected strains of lactic acid bacteria to develop new dairy products with functional properties due to the presence of pyroglutamic and butyric acid.