Proteomic characterization of kefir milk by two dimensional electrophoresis followed by mass spectrometry

Kefir is a fermented milk beverage produced by the symbiotic action of some bacterial species and yeasts. This microbial association is naturally present in kefir grains, and the micro-organisms involved are held together by a matrix of complex sugars known as “kefiran”. Thanks to the fermentative process, the kefir milk is rich in nutraceutical substances such as amino acids, vitamins, and mineral salts. However, the most valuable compounds of kefir fermentation are mainly small bioactive peptides as the resulting products of proteolytic release from milk proteins (caseins and whey proteins). Much health-promoting and therapeutic effects have been attributed to bioactive peptides, which can reach the portal circulation, exerting several physiological functions, otherwise they remain intact in the intestinal tract, supporting the microbiota. For this reason, kefir milk is considered a natural probiotic. Many bioactive peptides are involved in the immunomodulation, antimicrobial, hypocholesterolemic, anticarcinogenic, and hypotensive effect. Therefore, considering the exciting properties of kefir milk, in this work, a proteomic analysis by two-dimensional electrophoresis followed by mass spectrometry, has been performed. As a result, milk-derived bioactive peptides were identified in commercial kefir milk from organic farming. In particular, fragments deriving from β-casein, αs1- and αs2-caseins with potential beneficial effects on human health, have been detected