Traditional Kefir Research Articles

Evaluation of the probiotic, technological, safety attributes, and GABA-producing capacity of microorganisms isolated from Iranian milk kefir beverages.

Kefir beverage has beneficial microorganisms that have health-giving properties; therefore, they have a good potential to be probiotic. This study evaluated the probiotic potential, technological, and safety characteristics of Enterococcus faecalis, Lactococcus lactis, and Pichia fermentans isolated from traditional kefir beverages. First, isolates were evaluated in terms of resistance to acid, alkali, bile salts, trypsin, and pepsin of the gastrointestinal tract. The auto-aggregation and co-aggregation ability of isolates were measured using spectrophotometry. Antimicrobial activities were assayed against important food-borne pathogens using the agar well diffusion method. Moreover, gamma-aminobutyric acid (GABA) production was investigated by thin-layer chromatography (TLC). Among the isolates, P. fermentans had an 85% total survival rate, but its amount reached below 6 log CFU/ml which is considered non-resistant, and it showed the highest auto-aggregation (74.67%). Moreover, only L. lactis showed antimicrobial activity and had the highest co-aggregation with E. coli PTCC 1338 (54.33%) and L. monocytogenes ATCC 7644 (78%). Finally, an evaluation of the technological and safety characteristics of the strains showed that the strains produced GABA and were safe. Although the isolates were not resistant to the gastrointestinal tract, their supernatant contained valuable natural compounds, including antioxidants, GABA, and antimicrobials, which can be used to produce functional foods and medicines. In addition, other approaches, such as increasing the initial number of strains, using foods as carriers of isolates, and encapsulating the isolates, can effectively increase the survivability of isolates in the gastrointestinal tract.

Evaluation of kefir grain microbiota, grain viability, and bioactivity from fermenting dairy processing by-products

Four dairy foods processing by-products (acid whey permeate (AWP), buttermilk (BM), sweet whey permeate (SWP), and sweet whey permeate with added milk fat globule ingredient (SWP+MFGM)) were fermented for 4 weeks and compared with traditional kefir milks for production of novel kefir-like dairy products. AU: Sweet whey permeates and SWP supplemented with 1.5% milk fat globule membrane (MFGM) showed to be the most viable by-products for kefir grain fermentation, exhibiting diverse abundance of traditional kefir microorganisms and positive indicators of bioactive properties. Grain viability was assessed with shotgun metagenomics, texture profile analysis, live cell counts, and scanning electron microscopy. Assessed bioactivities of the kefir-like products included antibacterial, antioxidant, potential anticancerogenic properties, and membrane barrier effect on human colorectal adenocarcinoma Caco-2 cells. All kefir grains were most abundant in Lactobacillus kefiranofaciens when analyzed with shotgun metagenomics. When analyzed with live cell counts on selective media, AWP kefir-like product had no countable Lactococcus spp. indicating suboptimal conditions for kefir grain microbiota survival and application for fermented dairy starter culture bacterium. Live cell counts were affirmed with kefir grain surface scanning electron microscopy images. SWP had the most adhesive kefir grain surface while SWP+MFGM had the largest exopolysaccharide (EPS) yield from grain extraction. All kefir and kefir-like products were able to achieve a 6-log reduction against Listeria innocua and Escherichia coli. Traditional milk kefirs had the highest antioxidant capacity for 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. AWP had a significantly higher DPPH antioxidant activity and SWP had the lowest Trolox equivalence concentration in the ABTS assay. Sweet whey and supplemented milk fat sweet whey had upregulation of Cldn-1 and Ocln-1 gene expression, which correspond with a significant increase in transepithelial electrical resistance.

Use of reconstituted kefir consortia to determine the impact of microbial composition on kefir metabolite profiles

Kefir is fermented traditionally with kefir grains, but commercial kefir production often relies on fermentation with planktonic cultures. Kefir has been associated with many health benefits, however, the utilization of kefir grains to facilitate large industrial production of kefir is challenging and makes to difficult to ensure consistent product quality and consistency. Notably, the microbial composition of kefir fermentations has been shown to impact kefir associated health benefits. This study aimed to compare volatile compounds, organic acids, and sugar composition of kefir produced through a traditional grain fermentation and through a reconstituted kefir consortium fermentation. Additionally, the impact of two key microbial communities on metabolite production in kefir was assessed using two modified versions of the consortium, with either yeasts or lactobacilli removed. We hypothesized that the complete kefir consortium would closely resemble traditional kefir, while the consortia without yeasts or lactobacilli would differ significantly from both traditional kefir and the complete consortium fermentation. Kefir fermentations were examined after 12 and 18 h using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) to identify volatile compounds and high performance liquid chromatography (HPLC) to identify organic acid and sugar composition. The traditional kefir differed significantly from the kefir consortium fermentation with the traditional kefir having 15–20 log2(fold change) higher levels of esters and the consortium fermented kefir having between 1 and 3 log2(fold change) higher organic acids including lactate and acetate. The use of a version of kefir consortium that lacked lactobacilli resulted in between 2 and 20 log2(fold change) lower levels of organic acids, ethanol, and butanoic acid ethyl ester, while the absence of yeast from the consortium resulted in minimal change. In summary, the kefir consortium fermentation is significantly different from traditional grain fermented kefir with respect to the profile of metabolites present, and seems to be driven by lactobacilli, as evidenced by the significant decrease in multiple metabolites when the lactobacilli were removed from the fermentation and minimal differences observed upon the removal of yeast.

Comparison of the relative impacts of acute consumption of an inulin-enriched diet, milk kefir or a commercial probiotic product on the human gut microbiome and metabolome

It has been established that the human gut microbiota is central to health, and, consequently, there has been a growing desire to positively modulate its composition and/or function through, for example, the use of fermented foods, prebiotics or probiotics. Here, we compare the relative impact of the daily consumption of an inulin-enriched diet (n = 10), a commercial probiotic-containing fermented milk product (FMP) (n = 10), or a traditional kefir FMP (n = 9), over a 28-day period on the gut microbiome and urine metabolome of healthy human adults. None of the treatments resulted in significant changes to clinical parameters or biomarkers tested. However, shotgun metagenomic analysis revealed that kefir consumption resulted in a significant change in taxonomy, in the form of an increased abundance of the sub-dominant FMP-associated species Lactococcus raffinolactis, which further corresponded to shifts in the urine metabolome. Overall, our results indicated that daily consumption of a single portion of kefir alone resulted in detectable changes to the gut microbiota and metabolome of consumers.

Iranian traditional kefir beverage: isolation and identification of beneficial microorganisms and evaluation of antimicrobial activity against food-borne pathogens

Purpose Kefir is a traditional fermented dairy beverage that has numerous health benefits due to the presence of bacteria and yeasts in an exopolysaccharide matrix. This study aims to isolate and identify beneficial microorganisms and evaluate the antimicrobial activity of kefir beverage against two important food-borne pathogens including Salmonella Typhimurium and Listeria monocytogenes. Design/methodology/approach Microorganisms were identified by the polymerase chain reaction with specific primers, and antimicrobial activity was evaluated by the disk diffusion method. Findings The following microorganisms were identified as natural inhabitants of the kefir grains: Leuconostoc lactis, Lactococcus lactis subspecies lactis, Streptococcus cremoris, Enterococcus faecalis, Enterococcus faecium, Lactobacillus helveticus, Leuconostoc mesenteroides, Lactobacillus fermentum, Lactobacillus reuteri, Lactobacillus plantarum, Lactobacillus casei, Bifidobacterium langum, Saccharomyces cerevisiae and Pichia fermentas. Also, the results obtained from the disk diffusion method showed the inhibitory effect of kefir milk on Salmonella Typhimurium and Listeria monocytogenes with an inhibitory average diameter of 8.3 ± 4–9.1 ± 2.8 and 3.4 ± 3–6.6 ± 3 mm, respectively. Originality/value The results of this study showed that Iranian traditional kefir beverage contained different species of lactic acid bacteria and yeasts and has antimicrobial activity against two important food-borne pathogens, Salmonella Typhimurium and Listeria monocytogenes, which the highest inhibitory effect was observed against Salmonella Typhimurium.

Proximate Composition and Antimicrobial Activity of Kefir Produced from Cow’s and Almond Milk

Fermented foods are an important diet component of people around the world. Kefir, or fermented milk, is popular worldwide due to its high nutritional value, with cow's milk being the common substrate for traditional kefir fermentation. However, the scarcity of animal-based milk in some countries, plus cultural, religious, and health reasons, have seen non-dairy milk kefir from almond milk gaining popularity among consumers globally. This study aimed to evaluate and compare the proximate composition and anti-microbial activity of kefir produced from 100% cow or 100% almond or an equal (1:1) mixture of both kinds of milk. This study used the AOAC 2000 method for the proximate analysis, while the agar well diffusion method examined the anti-microbial activity of the milk samples against Escherichia coli, Staphylococcus aureus, and Salmonella typhi. Results revealed that the three kefir samples showed significantly different (p<0.05) moisture, total dietary fiber, and fat contents and were within the CODEX acceptable range for kefir. All samples exhibited varying degrees of inhibition between the different pathogens. The diameters of the inhibition zone of the tested kefir samples were significantly different toward Salmonella typhi (p<0.05), with the mixture of almond and cow milk notably producing better inhibition towards all tested bacteria. The above-said milk mixture also gave a better overall nutrient profile (lower fat and higher fibre). While almond milk might be a suitable substrate for kefir, it was not effectively inhibitory for all bacteria. The overall results thus conveyed the promising use of almond and cow milk mixture as an alternative substrate for kefir fermentation, further supporting its potential use as a probiotics source.

Consumption of kefir made with traditional microorganisms resulted in greater improvements in LDL cholesterol and plasma markers of inflammation in males when compared to a commercial kefir: a randomized pilot study.

Kefir has long been associated with health benefits; however, recent evidence suggests that these benefits are dependent on the specific microbial composition of the kefir consumed. This study aimed to compare how consumption of a commercial kefir without traditional kefir organisms and a pitched kefir containing traditional organisms affected plasma lipid levels, glucose homeostasis, and markers of endothelial function and inflammation in males with elevated LDL cholesterol. We utilized a crossover design in n = 21 participants consisting of two treatments of 4 weeks each in random order separated by a 4-week washout. Participants received either commercial kefir or pitched kefir containing traditional kefir organisms for each treatment period. Participants consumed 2 servings of kefir (350 g) per day. Plasma lipid profile, glucose, insulin, markers of endothelial function, and inflammation were measured in the fasting state before and after each treatment period. Differences within each treatment period and comparison of treatment delta values were performed using paired t tests and Wilcoxon signed-rank test, respectively. When compared to baseline, pitched kefir consumption reduced LDL-C, ICAM-1, and VCAM-1, while commercial kefir consumption increased TNF-α. Pitched kefir consumption resulted in greater reductions in IL-8, CRP, VCAM-1, and TNF-α when compared to commercial kefir consumption. These findings provide strong evidence that microbial composition is an important factor in the metabolic health benefits associated with kefir consumption. They also provide support for larger studies examining these to assess whether traditional kefir organisms are necessary to confer health benefits to individuals at risk of developing cardiovascular disease.

Application of Ultrafiltration to Produce Sheep's and Goat's Whey-Based Synbiotic Kefir Products.

Membrane filtration technologies are the best available tools to manage dairy byproducts such as cheese whey, allowing for the selective concentration of its specific components, namely proteins. Their acceptable costs and ease of operation make them suitable for application by small/medium-scale dairy plants. The aim of this work is the development of new synbiotic kefir products based on sheep and goat liquid whey concentrates (LWC) obtained by ultrafiltration. Four formulations for each LWC based on a commercial kefir starter or traditional kefir, without or with the addition of a probiotic culture, were produced. The physicochemical, microbiological, and sensory properties of the samples were determined. Membrane process parameters indicated that ultrafiltration can be applied for obtaining LWCs in small/medium scale dairy plants with high protein concentration (16.4% for sheep and 7.8% for goats). Sheep kefirs showed a solid-like texture while goat kefirs were liquid. All samples presented counts of lactic acid bacteria higher than log 7 CFU/mL, indicating the good adaptation of microorganisms to the matrixes. Further work must be undertaken in order to improve the acceptability of the products. It could be concluded that small/medium-scale dairy plants can use ultrafiltration equipment to valorize sheep's and goat's cheese whey-producing synbiotic kefirs.

Determining the safety of kefir grains for public health

In this study, kefir grains and kefir produced from contaminated grains were investigated in terms of food safety. For this aim, traditional kefir grains were collected from distinct parts of Turkey, and their pathogenicity was examined. Typical and non-typical colonies were isolated on Violet Red Bile Agar and identified for the first time at species level. Antibiotic resistance and hemolytic activity of the isolates were also determined. Coliform and pathogenic bacteria was found in 19 out of 30 kefir grains tested (63.33%). Although Hafnia paralvei was the predominant group, Klebsiella oxytoca, Citrobacter freundii, Serratia liquefaciens, and Escherichia coli were also identified among the 27 strains as the pathogenic bacteria. It was found that the bacterial count of kefir produced from two kefir grains containing pathogenic bacteria was 8.44 log CFU/mL and 8.20 log CFU/mL at the end of the 10th day. All isolates were sensitive to ciprofloxacin, nalidixic acid, meropenem, and ertapenem but resistant to ampicillin and vancomycin. Furthermore, all strains were found to be β-hemolytic in that study. As a result, it was determined that traditionally produced kefir can be risky in terms of food safety due to contaminated kefir grains and this risk continues throughout consumption.

Therapeutic and Dietary Support for Gastrointestinal Tract Using Kefir as a Nutraceutical Beverage: Dairy-Milk-Based or Plant-Sourced Kefir Probiotic Products for Vegan and Lactose-Intolerant Populations

Kefir is a fermented milk beverage different in consistency and taste from other popular milk-product yogurt. Unlike yogurt prepared using lactic acid bacteria in fermentation, milk is fermented for kefir production using preculture in the form of kefir grains. Therefore, the metabolic activities of a mixed culture, including strains of bacteria and yeast, contribute to the probiotic characteristics in kefir. This article is based on the review of published studies on the functionality and nutraceutical properties of kefir. The therapeutic and dietary properties of kefir beverage and its probiotic strains have been discussed for their several health benefits. Concise selected information mostly from recent reports has been presented for two categories of kefir products: milk used for the production of dairy-based traditional kefir beverages for the lactose-tolerant population, and the plant-sourced substrates used for the production of dairy-free kefir beverages for lactose-intolerant and vegan consumers.

Physical and chemical properties, structural characterization and nutritional analysis of kefir yoghurt.

Scanning electron microscopy (SEM), Confocal laser scanning microscopy (CLSM) and low field nuclear magnetic resonance (LF-NMR) were used to analyse the relationship between the chemical, texture, rheology, microstructure and water distribution of kefir (yeast, acetic acid bacteria and Lactobacillus plantarum) yoghurt fermented by mixed bacteria and L. plantarum L1 fermented yoghurt. This work was conducted to prepare a real champagne yoghurt and explore the difference between it and ordinary yoghurt. The nutritional evaluation of the two treatment groups was carried out by amino acid analysis, and the volatile flavour substances of the two treatment groups were detected by solid phase microextraction (SPME)-gas chromatograph (GC)-mass spectrometry (MS). Results showed that the addition of acetic acid bacteria and yeast increased the water content of kefir, resulting in a decrease in its water-holding rate. Moreover, the increase in acidity weakened the connection between the protein networks, the flocculent protein structure was not more densely stacked than the L1 group, and the internal bonds were unstable. The rheological results showed that the apparent viscosity decreased faster with the increase in shear force. The CLSM and LF-NMR showed that the hydration and degree of freedom of kefir yoghurt protein decreased, resulting in an increased protein network density. The SEM showed that the cross-linking between kefir casein clusters was considerably tight to form small chains, the pore distribution was uneven, and a weak cheese structure was formed. In addition, the volatile flavour substances in the kefir group increased the phenylethyl alcohol, isobutanol, and isoamyl alcohol compared with those in the L1 group, with a slight refreshing taste brought by alcohol and special soft malt alcohol aroma and rose aroma not found in ordinary yoghurt, which was more in line with the characteristics and taste of traditional kefir champagne yoghurt. Graphical Abstract.

Effects of commercial and traditional kefir supplementation on apparent total tract macronutrient digestibility and the fecal characteristics, metabolites, and microbiota of healthy adult dogs.

Kefir is a fermented dairy beverage that has been consumed by humans for centuries, but poorly studied in pets. The objective of this study was to determine the effects of commercial or traditional kefir supplementation on apparent total tract macronutrient digestibility (ATTD) and fecal characteristics, microbiota populations, and metabolite and immunoglobulin (Ig) A concentrations of healthy adult dogs. Twelve healthy adult dogs (5.67 ± 1.72 yr, 7.27 ± 1.15 kg) were used in a replicated 3 × 3 Latin square design (n = 12/group). All dogs were fed a commercial diet and allotted to 1 of 3 treatments (60 mL/d): 2% reduced-fat milk treated with lactase [CNTL; 4.57E + 03 lactic acid bacteria (LAB) colony-forming units (CFU)/mL], commercial kefir (C-Kefir; 6.95E + 04 LAB CFU/mL), or traditional kefir brewed daily from 2% reduced-fat milk and kefir grains (T-Kefir; 1.79E + 09 LAB CFU/mL). The experiment was composed of three 28-d periods, with each consisting of a 22-d transition phase, a 5-d fecal collection phase, and 1 d for blood collection. Fecal samples were collected for determination of ATTD and fecal pH, dry matter, microbiota, and metabolite, and IgA concentrations. Data were analyzed using the Mixed Models procedure of SAS 9.4. The main effects of treatment were tested, with significance set at P ≤ 0.05 and trends set at P ≤ 0.10. Kefir products differed in microbial density and profile, but fecal microbiota populations were weakly impacted. Bacterial alpha diversity tended to be greater (P = 0.10) in dogs fed T-Kefir than those fed CNTL. Bacterial beta diversity analysis identified a difference (P < 0.0004) between dogs-fed CNTL and those fed C-Kefir. Dogs-fed C-Kefir tended to have a greater (P = 0.06) relative abundance of Fusobacteriota than those fed CNTL or T-Kefir. Dogs-fed T-Kefir had a greater (P < 0.0001) relative abundance of Lactococcus than those fed CNTL or C-Kefir. Dogs-fed T-Kefir also tended to have a lower (P = 0.09) relative abundance of Escherichia Shigella and greater (P = 0.09) relative abundance of Candidatus stoquefichus than dogs-fed CNTL or C-Kefir. Dogs-fed C-Kefir tended to have lower (P = 0.08) fecal valerate concentrations than those fed CNTL or T-Kefir. All other measures were unaffected by kefir treatments. Our results suggest that kefir supplementation had minor effects on the fecal microbiota populations and fecal metabolite concentrations of healthy adult dogs without impacting ATTD, fecal characteristics, or fecal IgA concentrations.

Differences of the Polysaccharides in Kefir Grains from Different Origins Subcultured in Goat Milk

Polysaccharides are one of the major building blocks of traditional kefir grains, and their properties are often affected by the geographical origin and substrates used. After subculturing in goat milk for 4 months, spectroscopic, chromatographic, and microscopic imaging techniques were employed for the analysis of the structure of polysaccharides in kefir grains originated from different countries. Fourier transform infrared spectroscopy showed that all polysaccharides were classified into β-d-glucopyranose, and the sugar configuration was β-type. The particle size, molecular weight distributions, and thermal stability of the polysaccharides from kefir grains of CN and DE were apparently higher than those from the USA. The surface structure of polysaccharides in kefir grains of CN and DE was smoother than that of the one from the USA. The results of this study indicated that the molecular and conformational characteristics of polysaccharides were different for kefir grains originated from the three countries when subcultured in goat milk.

Consumption of the cell-free or heat-treated fractions of a pitched kefir confers some but not all positive impacts of the corresponding whole kefir.

Kefir consumption can have many metabolic health benefits, including, in the case of specific kefirs, improvements in plasma and liver lipid profiles. Our group has previously shown that these health benefits are dependent on the microbial composition of the kefir fermentation, and that a pitched kefir (PK1) containing specific traditional microbes can recapitulate the health benefits of a traditional kefir. In this study we investigated how different preparations of kefir impact cholesterol and lipid metabolism and circulating markers of cardiovascular disease risk and determine if freeze-drying impacts health benefits relative to past studies. Eight-week-old male and female C57Bl/6 mice were fed a high fat diet (40% kcal from fat) supplemented with one of 3 freeze-dried kefir preparations (whole kefir, cell-free kefir, or heat-treated kefir) for 8 weeks prior to analysis of plasma and liver lipid profiles, circulating cardiovascular disease (CVD) biomarkers, cecal microbiome composition, and cecal short-chain fatty acid levels. These groups of mice were compared to others that were fed a control low-fat diet, control high fat diet or high fat diet supplemented with milk, respectively. All kefir preparations lowered plasma cholesterol in both male and female mice, while only whole kefir lowered liver cholesterol and triglycerides. Plasma vascular cell adhesion molecule 1 (VCAM-1) was lowered by both whole kefir and heat-treated kefir in male mice but not females, while c-reactive protein (CRP) was unchanged across all high fat diet fed groups in males and females. These results indicate that some of the metabolic benefits of consumption of this kefir do not require whole kefir while also indicating that there are multiple compounds or components responsible for the different benefits observed.

Isolation and screening of high‐quality lactic acid bacteria and yeast strains in kefir grains and preparation of kefir compound fermentation starter

In this study, a total of ten strains of kefir grains were isolated. Lactic acid bacteria and yeast were the research subjects. The final compound fermentation starter was produced using Leu. Mesenteroides, Lactobacillus kefir, Lactobacillus casei, and K. marxianus. The fermented milk of the compound fermentation starter and kefir grains were compared in curding time, acidity, water holding capacity (WHC), ethanol content, the viability of strains, and sensory score. The results showed that the quality of the fermented milk was similar, but the kinds of volatile aroma components in the kefir produced by the compound strain starter were significantly more than those of the kefir grains. The result of this study will help simplify and stabilize the industrial production of kefir, and provide a reference for the development of different flavored yogurt products. Novelty impact statement The dominant kefir grain strains were divided to create the strain compound starter, which can be used in place of kefir grains. It can ferment and produce a milk drink with similar characteristics to traditional kefir grains. The dairy industry can develop using strain starters to overcome the limitations of kefir grains and produce kefir products with consistently high quality.

Investigation of changes in culturable lactic microflora during freeze storage in cow and goat milk kefirs by high‐throughput sequencing

This study determined changes in the live lactic microflora of cow and goat milk kefirs, traditionally produced using kefir grain and freeze stored for 30 days, using high-throughput sequencing. In kefir grains, 71.29% Lactococcus, 16.27% Enterococcus, and 12.3% Serratia were found in the M17 agar, and 69.93% Lacticaseibacillus and 24.54% Lactobacillus were found in MRS agar. In the M17 agar of cow milk kefir, 78.26% Lactococcus was found on day 0, and this rate was 91.68%, 87.98%, and 88.14%, on the 7th, 14th, and 30th days, respectively. As for goat milk kefir, Lactococcus levels were 82.98%, 93.28%, 87.77%, and 84.92%, respectively. On the MRS agar in cow milk kefirs, Lacticaseibacillus levels were found as 56.98%, 61.21%, 87.54%, and 75.50%, on days 0, 7, 14, and 30 of storage, respectively, while the rates were 48.95%, 77.02%, 87.85%, and 83.38% for goat milk kefirs, respectively. As a result, although kefir beverages frozen at −25°C contain sufficient levels of Lactobacillus and Lactococcus, it has been determined that the genus Serratia, which is one of the main spoilage factors in dairy products, is also increasing. Novelty impact statement In this study, the changes in the living lactic microflora during the frozen storage of traditional kefir beverages, whose production is increasing, were determined by high-throughput sequencing. It is thought that it is important to determine the effect of the freezing process on the viability of lactic acid bacteria, which are thought to have probiotic properties, for the long-term storage of these beverages. However, while lactic acid bacteria maintain their viability, it should be taken into account that microorganisms that are resistant to freeze conditions and cause spoilage can also develop.

Traditional Grain-Based vs. Commercial Milk Kefirs, How Different Are They?

Traditional kefir, which is claimed for health-promoting properties, is made from natural grain-based kefir, while commercial kefirs are made of defined mixtures of microorganisms. Here, approaches are described how to discriminate commercial and traditional kefirs. These two groups of kefirs were characterized by in-depth analysis on the taxonomic and functional level. Cultivation-independent targeted qPCR as well as next-generation sequencing (NGS) proved a completely different microbial composition in traditional and commercial kefirs. While in the traditional kefirs, Lactobacillus kefiranofaciens was the dominant bacterial species, commercial kefirs were dominated by Lactococcus lactis. Volatile organic compounds (VOCs) analysis using headspace-gas chromatography-ion mobility spectrometry also revealed drastic differences between commercial and traditional kefirs; the former built a separate cluster together with yogurt samples. Lactose and galactose concentrations in commercial kefirs were considerably higher than in traditional kefirs, which is important regarding their health properties for people who have specific intolerances. In summary, the analyzed commercial kefirs do not resemble the microbial community and metabolite characteristics of traditional grain-based kefir. Thus, they may deliver different functional effects to the consumers, which remain to be examined in future studies.

Volatilomics-Based Microbiome Evaluation of Fermented Dairy by Prototypic Headspace-Gas Chromatography-High-Temperature Ion Mobility Spectrometry (HS-GC-HTIMS) and Non-Negative Matrix Factorization (NNMF).

Fermented foods, such as yogurt and kefir, contain a versatile spectrum of volatile organic compounds (VOCs), including ethanol, acetic acid, ethyl acetate, and diacetyl. To overcome the challenge of overlapping peaks regarding these key compounds, the drift tube temperature was raised in a prototypic high-temperature ion mobility spectrometer (HTIMS). This HS-GC-HTIMS was used for the volatilomic profiling of 33 traditional kefir, 13 commercial kefir, and 15 commercial yogurt samples. Pattern recognition techniques, including principal component analysis (PCA) and NNMF, in combination with non-targeted screening, revealed distinct differences between traditional and commercial kefir while showing strong similarities between commercial kefir and yogurt. Classification of fermented dairy samples into commercial yogurt, commercial kefir, traditional mild kefir, and traditional tangy kefir was also possible for both PCA- and NNMF-based models, obtaining cross-validation (CV) error rates of 0% for PCA-LDA, PCA-kNN (k = 5), and NNMF-kNN (k = 5) and 3.3% for PCA-SVM and NNMF-LDA. Through back projection of NNMF loadings, characteristic substances were identified, indicating a mild flavor composition of commercial samples, with high concentrations of buttery-flavored diacetyl. In contrast, traditional kefir showed a diverse VOC profile with high amounts of flavorful alcohols (including ethanol and methyl-1-butanol), esters (including ethyl acetate and 3-methylbutyl acetate), and aldehydes. For validation of the results and deeper understanding, qPCR sequencing was used to evaluate the microbial consortia, confirming the microbial associations between commercial kefir and commercial yogurt and reinforcing the differences between traditional and commercial kefir. The diverse flavor profile of traditional kefir primarily results from the yeast consortium, while commercial kefir and yogurt is primarily, but not exclusively, produced through bacterial fermentation. The flavor profile of fermented dairy products may be used to directly evaluate the microbial consortium using HS-GC-HTIMS analysis.

Nutritional value, sensory properties, and antioxidant activity of a traditional kefir produced with Arthrospira platensis

Arthrospira platensis is a microalgae generally known as a source of bioactive compounds and protein. The aim of this study is to evaluate the nutritional value, sensory characteristics, and antioxidant activity of traditional kefir by addition of A. platensis. In the study, the traditional kefir samples were prepared by the addition of A. platensis at 0.05%, 0.1%, 0.5%, 1%, and 2% (w/v) by considering generally recommended daily intake rate and consumer's acceptability. The sensory analysis scores showed that kefir with 0.05% and 0.1% A. platensis have the highest score, in which case the protein in the kefir slightly increased from 27 to 37 mg/ml. The addition of 1% A. platensis to kefir was found to increase amino acid contents. Some slight differences in calcium content were observed; however, there was a fourfold increase in iron. Palmitic and oleic acids (28.94% and 19.04%) were the most abundant fatty acids. The result indicated that A. platensis addition increased the antioxidant activities (FRAP and DPPH) of kefir, and addition of traditional kefir by A. platensis is a suitable way to increase the nutritional value of kefir. Practical applications Kefir is well-known, nutritional and functional fermented beverage that has a unique taste and high nutritional quality. Arthrospira platensis also is known to have been consumed since ancient times and has come to the fore especially in recent years due to its essential amino acids, fatty acids, vitamins, and minerals. Although both, kefir and A. platensis, have strong and weak sides, adding different levels of A. platensis to traditional kefir increased amino acid contents, iron, fatty acid, and antioxidant activities. In this study, the nutritional effects of the addition of an acceptable level of A. platensis to traditional kefir were reported.

Probiotics in the gut-skin axis – the case of kefir

The intestinal microbiota is linked to important functions in the host. Alterations in its composition and/or its by-products, causing loss of homeostasis, contribute to dysfunctions in other organic systems, including the skin, hence suggesting a gut-skin relationship. The oral administration of probiotics, widely associated with improved intestinal health, can act through an immunomodulatory response, both locally and systemically, presenting itself as potentially beneficial in inflammatory skin diseases such as atopic dermatitis. Traditional kefir, consumed for centuries as a health-promoting natural food, has its biological activity attributed both to the presence of a complex microbiota and to the action of the metabolites released during fermentation. The biological activity of kefir has been demonstrated in part by its ability to positively impact the intestinal microbiota, mainly based on animal models and in vitro, thus providing limited information. The nutritional and microbiological value of kefir makes its application as a probiotic in the gut-skin relationship a topic of of significant interest. This review aimed to explore the impact of probiotics as regulators of the gut-skin axis, focusing on the current knowledge of kefir as a health-promoting food. Keywords: kefir, probiotic, gut-skin axis, skin health, atopic dermatitis