Investigation of changes in milk protein n-glycan and free milk oligosaccharide profiles during kefir fermentation and storage processes

Kefir is an ancient food source based on the Caucasus mountains. Kefir is mainly produced by fermentation of kefir microorganisms using cow's milk. There are many studies showing the benefits of kefir to human health. The changes that occur in important components of milk during kefir production are not clearly known. In this study, it was aimed to examine the differences of N-glycans found in milk glycoproteins and free milk oligosaccharides in the process during the fermentation and storage of kefir. For this purpose, N-glycans were extracted from milk glycoproteins by an enzymatic process for each period during the fermentation and storage of kefir and their analyzes were performed by MALDI-MS. Similarly, free milk oligosaccharides in milk were also extracted from samples during fermentation and storage of kefir and analyzed. In total, 57 N-glycans and 19 free milk oligosaccharides were characterized in the analysis, and their changes in the process were determined. Statistical analyzes showed that there were significant changes in 7 different N-glycan types H5N4, H8N2, H5N4F1, H4N5F1, H3N6F1, H9N2, H4N5S1F1, and two different oligosaccharide types (lactose, Hex2, and triose, Hex3) during the process (p<0.05). This study is expected to assist in the detailed evaluation of clinical and mechanistic studies on kefir.