Probiotics have been used for decades to alleviate the negative side-effects of oral antibiotics, but our mechanistic understanding on how they work is so far incomplete. Here, we performed a metagenomic analysis of the fecal microbiota in participants who underwent a 14-d Helicobacter pylori eradication therapy with or without consumption of a multi-strain probiotic intervention (L. paracasei CNCM I-1518, L. paracasei CNCM I-3689, L. rhamnosus CNCM I-3690, and four yogurt strains) in a randomized, double-blinded, controlled clinical trial. Using a strain-level analysis for detection and metagenomic determination of replication rate, ingested strains were detected and replicated transiently in fecal samples and in the gut during and following antibiotic administration. Consumption of the fermented milk product led to a significant, although modest, improvement in the recovery of microbiota composition. Stratification of participants into two groups based on the degree to which their microbiome recovered showed i) a higher fecal abundance of the probiotic L. paracasei and L. rhamnosus strains and ii) an elevated replication rate of one strain (L. paracasei CNCMI-1518) in the recovery group. Collectively, our findings show a small but measurable benefit of a fermented milk product on microbiome recovery after antibiotics, which was linked to the detection and replication of specific probiotic strains. Such functional insight can form the basis for the development of probiotic-based intervention aimed to protect gut microbiome from drug treatments.

Healthy plant-based diets rich in fermentable residues may induce gas-related symptoms, possibly mediated by the gut microbiota. We previously showed that consumption of a fermented milk product (FMP) containing Bifidobacterium animalis subsp. lactis CNCM I-2494 and lactic acid bacteria improved gastrointestinal (GI) comfort in response to a flatulogenic dietary challenge in healthy individuals. To study the effects of the FMP on gut microbiota activity from those participants, we conducted a metatranscriptomic analysis of fecal samples (n = 262), which were collected during the ingestion of a habitual diet and two series of a 3-day high-residue challenge diet, before and following 28-days of FMP consumption. Most of the FMP species were detected or found enriched upon consumption of the product. FMP mitigated the effect of a flatulogenic diet on gas-related symptoms in several ways. First, FMP consumption was associated with the depletion of gas-producing bacteria and increased hydrogen to methane conversion. It also led to the upregulation of activities such as replication and downregulation of functions related to motility and chemotaxis. Furthermore, upon FMP intake, metabolic activities such as carbohydrate metabolism, attributed to B. animalis and S. thermophilus, were enriched; these activities were coincidentally found to be negatively associated with several GI symptoms. Finally, a more connected microbial ecosystem or mutualistic relationship among microbes was found in responders to the FMP intervention. Taken together, these findings suggest that consumption of the FMP improved the tolerance of a flatulogenic diet through active interactions with the resident gut microbiota.

Since ancient times, mare\'s milk has been widely used by many peoples. Thanks to its unique composition, it is now used in the nutrition of people with allergies to cow\'s milk, in the technologies of foods for special dietary uses, etc. To expand the range of products with useful properties, it is advisable to develop fermented milk products based on mare\'s milk. Numerous studies indicate that the use of fermented milk products provides various health benefits. And the use of probiotic cultures in the composition of starter cultures for fermented milk products allows you to add a number of functional properties to the product. However, the only fermented milk product available on the market from mare\'s milk is koumiss. Therefore, the development of new fermented milk products based on mare\'s milk is relevant and in demand. The aim of the study was to develop a fermented milk product based on mare\'s milk using an association consisting of yogurt starter culture and a probiotic strain of L. rhamnosus F. Material and methods. For the development of a fermented milk product based on mare\'s milk, the yogurt starter STBp (S. thermophilus and L. delbrueckii subsp bulgaricus) and the probiotic culture L. rhamnosus F (GenBank MN994629) from the collection of lactic acid and probiotic microorganisms of VNIMI were chosen. As a basis for the fermented milk product, mare\'s milk was used with the addition of dry mare\'s or dry cow\'s milk, pre-pasteurized at a temperature of 65±1 °C with a holding time of 30 min and cooled to a fermentation temperature of 37±1 °C. In the course of the work, the activity of acid formation during product fermentation, the duration of fermentation and the dynamics of the number of lactic acid bacteria and L. rhamnosus F probiotic strain during fermentation were studied, depending on the ratio of cultures in the ferment, the dose of the ferment introduced and the base for fermentation. The antimicrobial activity of the product was determined by agar well diffusion assay. Results. It was found that L. rhamnosus F has a low acid-forming activity, so the use of a combined starter culture (association) was proposed. It was determined that the addition of cow\'s milk powder to mare\'s milk positively affects the activity of acid formation; after 6 hours of fermentation, the pH value varied in the range of 4.6-4.83, and after 8 hours pH was 4.44-4.65. When dry mare\'s milk was added, the pH value after 8 hours of fermentation was in the range of 4.71-4.98 pH units. The influence of the amount of combined starter culture (association) and its cultures ratio, the duration of fermentation on the content of lactic acid bacteria, including the probiotic strain L. rhamnosus F in the fermented milk product based on mare\'s milk, was established. The largest amount of L. rhamnosus F was contained in the product fermented by 7% association with the ratio of cultures 1/4 and 1/6 and after 8 h it amounted to 7-9.5×108 CFU/cm3. Conclusion. Summarizing the results of the research, the technology of a fermented milk product based on mare\'s milk was developed: the amount of starter culture (associations) - 7%, the ratio of cultures - 1 part of the starter culture for yogurt and 6 parts of L. rhamnosus F (1/6), the fermentation temperature - 37±1 °C, the duration of fermentation - 6 hours with the addition of cow\'s milk powder and 8 hours with the addition of mare\'s milk powder. The developed fermented milk product has antimicrobial activity against opportunistic and pathogenic microorganisms E. coli ATCC 25922, S. aureus ATCC 6538, S. typhimurium ATCC 14028.

Machinery such as pumps used for the commercial production of fermented milk products cause vibrations that can spread to the fermentation tanks. During fermentation, such vibrations can disturb the gelation of milk proteins by causing texture defects including lumpiness and syneresis. To study the effect of vibrations on yogurt structure systematically, an experimental setup was developed consisting of a vibration exciter to generate defined vibrational states and accelerometers for monitoring. During the fermentation of skim milk, vibrations (frequency sweep: 25 to 1,005 Hz) were introduced at different pH (5.7 to 5.1, step width 0.1 units) for 200 s. Physical properties of set gels (syneresis, firmness) and resultant stirred yogurts (visible particles, rheology, laser diffraction) were analyzed. Vibrational treatments at pH 5.5 to 5.2 increased syneresis, gel firmness, and the number of large particles (d > 0.9 mm); hence, this period was considered critical. The particle number increased from 34 ± 5 to 242 ± 16 particles per 100 g of yogurt due to vibrations at pH 5.4. In further experiments, yogurts were excited with fixed frequencies (30, 300, and 1,000 Hz). All treatments increased syneresis, firmness, and particle formation. As the strongest effect was observed by applying 30 Hz, the amplitude was set to vibration accelerations of a = 5, 10, 15, 20, and 25 m/s2 in the final experiments. The number of large particles was increased due to each treatment and a positive correlation with the amplitude was found. We concluded that vibrations during gelation increase the collision probability of aggregating milk proteins, resulting in a compressed set gel with syneresis. Resultant stirred yogurts exhibit large particles with a compact structure leading to a reduced water-holding capacity and product viscosity.

We assessed the antimicrobial activity of reuterin produced in vitro in glycerol aqueous solutions in situ by Lactobacillus reuteri ATCC 53608 as part of a fermented milk product against starter (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus), spoilage (Penicillium expansum), pathogenic (Staphylococcus aureus Salmonella enterica ssp. enterica, and Listeria monocytogenes), and pathogen surrogate (Escherichia coli DH5α) microorganisms. We also assayed the influence of cold storage (28 d at 4°C) and reuterin on the color and rheology of the fermented milk product. We obtained maximum reuterin concentrations of 107.5 and 33.97 mM in glycerol aqueous solution and fermented milk product, respectively. Reuterin was stable throughout its refrigerated shelf life. Gram-positive microorganisms were more resistant to reuterin than gram-negative microorganisms. Penicillium expansum and Lactobacillus reuteri ATCC 53608 survived at concentrations up to 10 and 8.5 mM, respectively. Escherichia coli DH5α was the most sensitive to reuterin (0.9 mM). The presence of reuterin did not cause relevant changes in the quality parameters of the fermented milk product, including pH, acidity, soluble solids, color, and rheological aspects (storage and loss moduli and viscosity). This study demonstrated the viability of using Lactobacillus reuteri ATCC 53608 as a biopreservative in a fermented milk product through reuterin synthesis, without drastically modifying its quality parameters.