Bioactive peptides derived from milk proteins are an active research area. Exhibiting numerous positive physiological effects on digestive, cardiovascular, immune and nervous systems, these peptides thought to be one of the most promising ingredients for functional food. Generally, these peptides are inactive within the parent proteins and can be liberated during milk fermentation by the specific proteolytic systems of various Lactobacillus spp. Here we present the study of milk fermentation by Lactobacillus helveticus NK1, Lactobacillus rhamnosus F and Lactobacillus reuteri LR1 strains. It was demonstrated that the antioxidant activity of the milk fermented by these strains concomitantly increased with the strains’ proteolytic activity. For the angiotensin I-converting enzyme (ACE) inhibitory activity, the same tendency was not observed. Although the proteolytic activity of L. helveticus NK1 was two times higher than that of L. rhamnosus F, the milk fermented by these strains showed comparable ACE inhibition. The analysis of the peptide profiles of the fermented milk samples allowed us to hypothesize that some previously unreported peptides can be produced by L. rhamnosus F. In addition, it was demonstrated that these potential ACE-inhibiting peptides originated from the C-terminus of α_S2-casein.

The expansion of multiple drug resistant (MDR) strains of Klebsiella pneumoniae presents an immense threat for public health. Annually, this microorganism causes thousands of lethal nosocomial infections worldwide. Currently, it has been shown that certain strains of lactic acid bacteria (LAB) can efficiently inhibit growth of K. pneumoniae and the formation of its biofilms; however, the active principle of such action remains unknown. In the current article, the growth inhibition of MDR K. pneumoniae by two LAB—Limosilactobacillus reuteri LR1 and Lacticaseibacillus rhamnosus F—is demonstrated, and the nature of this inhibition studied at the level of exoproteome. This article shows that the exoproteomes of studied LAB contains both classically and non-classically secreted proteins. While for L. reuteri LR1 the substantial portion of classically secreted proteins was presented by cell-wall-degrading enzymes, for L. rhamnosus F only one out of four classically secreted proteins was presented by cell-wall hydrolase. Non-classically secreted proteins of both LAB were primarily metabolic enzymes, for some of which a possible moonlighting functioning was proposed. These results contribute to knowledge regarding antagonistic interaction between LAB and pathogenic and opportunistic microorganisms and set new perspectives for the use of LAB to control the spread of these microorganisms.

Lacticaseibacillus paracasei (formerly Lactobacillus paracasei) is a nomadic lactic acid bacterium (LAB) that inhabits a wide variety of ecological niches, from fermented foodstuffs to host-associated microenvironments. Many of the isolated L. paracasei strains have been used as single-strain probiotics or as part of a symbiotic consortium within formulations. The present study contributes to the exploration of different strains of L. paracasei derived from non-conventional isolation sources—the South African traditional fermented drink mahewu (strains MA2 and MA3) and kefir grains (strains KF1 and ABK). The performed microbiological, biochemical and genomic comparative analyses of the studied strains demonstrated correlation between properties of the strains and their isolation source, which suggests the presence of at least partial strain adaptation to the isolation environments. Additionally, for the studied strains, antagonistic activities against common pathogens and against each other were observed, and the ability to release bioactive peptides with antioxidant and angiotensin I-converting enzyme inhibitory (ACE-I) properties during milk fermentation was investigated. The obtained results may be useful for a deeper understanding of the nomadic lifestyle of L. paracasei and for the development of new starter cultures and probiotic preparations based on this LAB in the future.

The work presents the results of studies on the creation of a combined starter culture based on lactic and propionic acid bacteria and the functional properties of products based on it. It...

As a natural, symbiotic consortium of bacteria and yeasts, kefir grains provide a unique source of new probiotic microorganisms. In this work, three new isolates of lactobacilli, Lactobacillus helveticus and two strains of Lacticaseibacillus paracasei, were isolated from kefir grains originating from the North Caucasus region of Russia, and they were identified with biochemical and genetic methods. The enzyme-activity profiles were described for all strains, and the antimicrobial resistance and genetic determinants of antibiotic resistance were screened. During fermentation of cow’s milk, all three strains showed lower acid-forming activity but comparable proteolytic, antioxidant, and hypotensive activities in comparison with kefir starter culture.

This article presents new data on Bifidobacterium longum MC-42—a strain that has been actively used for the preparation of commercial dairy products in Russia for almost 40 years. It was demonstrated that this strain possesses high activities of β-galactosidase, α-glucosidase, and leucine arylaminidase; inhibits the growth of pathogens such as Salmonella typhimurium, Staphylococcus aureus, and Escherichia coli; and can efficiently remove cholesterol from the cultural medium. The resistance of B. longum MC-42 determined for 15 commonly used antibiotics was in agreement with those previously reported for Bifidobacterium spp. The absence of frequently transmittable antibiotic resistance genes in the genome and the lack of undesirable activity of β-glucuronidase proved the safe use of B. longum MC-42 as a probiotic and starter culture. Additionally, the impact of two growth-promoting additives—yeast extract or milk protein hydrolysate containing supplementation—on the B. longum MC-42 fermentation profile was assessed. The introduction of these additives increases the maximum attainable viable cell count by orders of magnitude, significantly changed the profile of aminopeptidase activities in extracellular extracts, and influenced the antioxidant and antihypertensive properties of the obtained fermented products.