Yeast-bacteria interactions in kefir fermentation. An integrated metabolomic and metagenomic approach

The multiple types of relationship that can occur between microorganisms in fermented foods lead to different patterns of metabolic products. Both yeasts and bacteria are frequently isolated from fermentation products and possess traits that may improve the quality of the food product itself, bringing benefits to the consumer. Probiotic bacteria have been long studied, and lately also commercialised as health promoting food ingredients. In recent years the use of yeasts as probiotic agents in food has also received increased attention. Kefir is a fermented milk produced from grains that comprise a specific and complex mixture of bacteria and yeasts that live in a symbiotic association. Since it has raised interest in the scientific community due to its numerous beneficial effects on health, in this study we isolated both bacteria and yeast strains from a locally-produced kefir in order to screen them based on their ability to grow in human gastrointestinal-related conditions in vitro. Then, we compared the differences in the ability of selected strains to release metabolic products with proven beneficial effects for the host such as short chain fatty acids (SCFA) during a month of co-culture in both rich and chemically defined media.