Scientists at the APC Microbiome Institute in Cork, Ireland, used DNA sequencing technologies to characterise the microbial populations present in kefir. They said the analysis yielded “interesting insights” regarding the presence of genes considered important for probiotics.
“We found genes such as EPS synthesis proteins, bile salt transporter proteins, adhesion proteins, mucus binding proteins and bacteriocins. These are all genes that would be sought after within probiotic strains and so it is notable that they are also present in kefir microbes,” Dr Paul Cotter, principal investigator at the APC Microbiome Institute and Teagasc Food Research Centre, told NutraIngredients.
The presence of these genes suggests that the Lactobacillus kefiranofaciens strains present in the kefirs have the potential to survive gastric transit, colonise the gut and inhibit the growth of pathogens, wrote the researchers.
Now that the presence of these genes in kefir has been established, Dr Cotter said that the next step was to conduct feeding studies to determine how kefir impacts on the composition and function of the gut microbiota, and health in general.
“The presence of the aforementioned genes is notable, however, we want to now back these up through feeding studies in a scientifically controlled manner to more specifically assess the health benefits,” he explained.
Kefir is a dairy beverage that is produced when a kefir grain, consisting of a consortium of micro-organisms, is added to milk to initiate natural fermentation. The grains ferment the milk, imparting their ‘friendly’ organisms to create the cultured product.
The consumption of kefir has been associated with various health benefits, including anti-carciogenic, anti-inflammatory and anti-pathogenic effects, as well as the alleviation of the symptoms of lactose intolerance and the reduction of cholesterol.
There is mounting evidence to suggest that the micro-organisms present in kefir exert at least some of these benefits, but there is a lack of understanding of the mechanisms responsible.
Historically, in order to study the micro-organisms that make up a product such as kefir, it was necessary to grow or ‘culture’ the microorganisms on agar plates. However, to get a good insight into an entire microbial community would require a “vast area of different agar-based approaches”, said Dr Cotter.
This research used sophisticated DNA sequencing technologies combined with metabolomics and flavour analysis to investigate how the microbial composition, gene content and flavour of kefir change over the course of 24-hour fermentation.
Microbial succession patterns observed
Besides detecting genes associated with probiotic functionalities, the study revealed that different microbes become dominant at different stages in the fermentation process. For example, metagenomic sequencing revealed that Lactobacillus kefiranofaciens was the dominant bacterial species in kefir during the early stages of fermentation, but that Leuconostoc mesenteroides became more prevalent in later stages.
Explaining why these changes in microbial structure occur, Dr Cotter said: “We established that it comes down to the metabolic pathways that different microbes have. One microbe may dominate at the beginning as it uses the raw materials in milk but will become less dominant as they are used up. This first microbe may produce by-products that another microbe can use and so it will become dominant then…so there are multiple layers of succession.”
The practical significance of this is that the flavour is dictated by the genes encoded with these dominant species. By changing the ratios of certain microbes, it is possible to optimise the flavour of the milk.
“Different kefirs - and the microbes therein - produce different flavours, for example fruity versus cheesey versus vinegar-life, so if the flavour is not pleasant, it can be altered by changing the microbiota composition,” said Dr Cotter.
The researchers said this finding could also be applied to optimise the health related attributes of kefir and other fermented foods.
“Microbial Succession and Flavor Production in the Fermented Dairy Beverage Kefir”
Authors: Aaron M. Walsh, Fiona Crispie, Kieran Kilcawley, Orla O’Sullivan, Maurice G. O’Sullivan, Marcus J. Claesson and Paul D. Cotter