The role of lactate on the immunomodulatory properties of the nonbacterial fraction of kefir

The identification of components responsible for the bioactive properties of functional foods is of central interest in the food industry. In particular, fermented dairy products that are of a health benefit to the consumer may exert those salutary effects through the constituent microorganisms per se and/or through other bioactive components. Kefir is a beverage obtained by the fermentation of milk with kefir grains containing different lactic- and acetic-acid bacteria plus yeasts. We studied the immunomodulatory capacity of the nonbacterial fraction of kefir through approaches involving biochemistry and cell biology. Lactate, a major microbial metabolic product, was identified as the component responsible for the modulation of certain innate immune epithelial response: At the concentrations found in kefir-fermented milk, lactate inhibits the activation of intestinal epithelial cells triggered by interleukin-1β, tumor necrosis factor-α, or flagellin. Lactate treatment furthermore abrogates NF-κB signaling in the cells, whose action could be responsible for the observed modulation of the inflammatory response. These findings provide a new perspective in the analysis of the biologic properties of kefir-fermented-milk products.