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.

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.

The Gut Commensal Escherichia coli Aggravates High-Fat-Diet-Induced Obesity and Insulin Resistance in Mice.

Changes in the gut microbiota have been linked to metabolic endotoxemia as a contributing mechanism in the development of obesity and type 2 diabetes. Although identifying specific microbial taxa associated with obesity and type 2 diabetes remains difficult, certain bacteria may play an important role in initiating metabolic inflammation during disease development. The enrichment of the family Enterobacteriaceae, largely represented by Escherichia coli, induced by a high-fat diet (HFD) has been correlated with impaired glucose homeostasis; however, whether the enrichment of Enterobacteriaceae in a complex gut microbial community in response to an HFD contributes to metabolic disease has not been established. To investigate whether the expansion of Enterobacteriaceae amplifies HFD-induced metabolic disease, a tractable mouse model with the presence or absence of a commensal E. coli strain was established. With an HFD treatment, but not a standard-chow diet, the presence of E. coli significantly increased body weight and adiposity and induced impaired glucose tolerance. In addition, E. coli colonization led to increased inflammation in liver and adipose and intestinal tissue under an HFD regimen. With a modest effect on gut microbial composition, E. coli colonization resulted in significant changes in the predicted functional potential of microbial communities. The results demonstrated the role of commensal E. coli in glucose homeostasis and energy metabolism in response to an HFD, indicating contributions of commensal bacteria to the pathogenesis of obesity and type 2 diabetes. The findings of this research identified a targetable subset of the microbiota in the treatment of people with metabolic inflammation. IMPORTANCE Although identifying specific microbial taxa associated with obesity and type 2 diabetes remains difficult, certain bacteria may play an important role in initiating metabolic inflammation during disease development. Here, we used a mouse model distinguishable by the presence or absence of a commensal Escherichia coli strain in combination with a high-fat diet challenge to investigate the impact of E. coli on host metabolic outcomes. This is the first study to show that the addition of a single bacterial species to an animal already colonized with a complex microbial community can increase severity of metabolic outcomes. This study is of interest to a wide group of researchers because it provides compelling evidence to target the gut microbiota for therapeutic purposes by which personalized medicines can be made for treating metabolic inflammation. The study also provides an explanation for variability in studies investigating host metabolic outcomes and immune response to diet interventions.

Opportunities and Challenges of Understanding Community Assembly in Spontaneous Food Fermentation.

Spontaneous fermentations that do not rely on backslopping or industrial starter cultures were especially important to the early development of society and are still practiced around the world today. While current literature on spontaneous fermentations is observational and descriptive, it is important to understand the underlying mechanism of microbial community assembly and how this correlates with changes observed in microbial succession, composition, interaction, and metabolite production. Spontaneous food and beverage fermentations are home to autochthonous bacteria and fungi that are naturally inoculated from raw materials, environment, and equipment. This review discusses the factors that play an important role in microbial community assembly, particularly focusing on commonly reported yeasts and bacteria isolated from spontaneously fermenting food and beverages, and how this affects the fermentation dynamics. A wide range of studies have been conducted in spontaneously fermented foods that highlight some of the mechanisms that are involved in microbial interactions, niche adaptation, and lifestyle of these microorganisms. Moreover, we will also highlight how controlled culture experiments provide greater insight into understanding microbial interactions, a modest attempt in decoding the complexity of spontaneous fermentations. Further research using specific in vitro microbial models to understand the role of core microbiota are needed to fill the knowledge gap that currently exists in understanding how the phenotypic and genotypic expression of these microorganisms aid in their successful adaptation and shape fermentation outcomes. Furthermore, there is still a vast opportunity to understand strain level implications on community assembly. Translating these findings will also help in improving other fermentation systems to help gain more control over the fermentation process and maintain consistent and superior product quality.

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.

Introduction: 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. Materials and methods: 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. Results: 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. Conclusion: 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.

Kefir microbial composition is a deciding factor in the physiological impact of kefir in a mouse model of obesity.

Kefir consumption has been demonstrated to improve lipid and cholesterol metabolism; however, our previous study identified that benefits vary between different commercial and traditional kefir. Here, we investigate the ability of pitched culture kefir, that is, kefir produced by a small number of specific strains, to recapitulate health benefits of a traditional kefir, in a diet-induced obesity mouse model, and examine how microbial composition of kefir impacts these benefits. Eight-week-old female C57BL/6 mice were fed a high-fat diet (40 % energy from fat) supplemented with one of five kefir varieties (traditional, pitched, pitched with no Lactobacillus, pitched with no yeast and commercial control) at 2 ml in 20 g of food for 8 weeks prior to analysis of plasma and liver lipid profiles, and liver gene expression profiles related to lipid metabolism. Both traditional and pitched kefir lowered plasma cholesterol by about 35 % (P = 0·0005) and liver TAG by about 55 % (P = 0·0001) when compared with commercial kefir despite no difference in body weight. Furthermore, pitched kefir produced without either yeast or Lactobacillus did not lower cholesterol. The traditional and pitched kefir with the full complement of microbes were able to impart corresponding decreases in the expression of the cholesterol and lipid metabolism genes encoding 3-hydroxy-3-methylglutaryl-coenzyme A reductase, PPARγ and CD36 in the liver. These results demonstrate that traditional kefir organisms can successfully be utilised in a commercial process, while highlighting the importance of microbial interactions during fermentation in the ability of fermented foods to benefit host health.

Kefir in the Prevention and Treatment of Obesity and Metabolic Disorders.

PURPOSE OF REVIEW: This review summarizes recent animal and human trials examining the potential for kefir to improve obesity, type 2 diabetes, dyslipidemia, and non-alcoholic fatty liver disease (NAFLD). Evidence for pathways affected and suggestions of possible mechanisms of action are also considered. RECENT FINDINGS: Human trials examining the ability of kefir to recapitulate metabolic health benefits previously observed in rodent models have found mixed results. Kefir has long been associated with improvements in health including obesity, diabetes, NAFLD, and dyslipidemia in preventative animal trials. While recent evidence from human trials supports a positive role of kefir in modulating diabetes-related markers, the impact of kefir consumption on markers of dyslipidemia, NAFLD, and body composition has been for the most part contradictory to animal findings. Variability in organisms for kefir fermentation poses a significant challenge in making meaningful comparisons. Recommendations for future well-controlled animal and human research are provided.

The Microbiota and Health Promoting Characteristics of the Fermented Beverage Kefir.

Kefir is a complex fermented dairy product created through the symbiotic fermentation of milk by lactic acid bacteria and yeasts contained within an exopolysaccharide and protein complex called a kefir grain. As with other fermented dairy products, kefir has been associated with a range of health benefits such as cholesterol metabolism and angiotensin-converting enzyme (ACE) inhibition, antimicrobial activity, tumor suppression, increased speed of wound healing, and modulation of the immune system including the alleviation of allergy and asthma. These reports have led to increased interest in kefir as a focus of research and as a potential probiotic-containing product. Here, we review those studies with a particular emphasis on the microbial composition and the health benefits of the product, as well as discussing the further development of kefir as an important probiotic product.