Abstract:

[Objective] This study was conducted to characterize the changes in whey protein profile during the fermentation process of traditional koumiss from Inner Mongolia. [Method] Traditional koumiss was prepared using mare milk collected from Xianghuang Banner, Xilin Gol League, Inner Mongolia, with fermentation temperature at （22±2） ℃, and manual mixing 5 times per day, 300 beats each time. The koumiss samples were taken every 12 h during the 0-96 h fermentation process, and whey protein was collected by centrifugation. Variations in Koumiss whey protein profile during the fermentation process were analyzed by the optimized SDS-PAGE. [Result] The optimized SDS-PAGE conditions were as follows: the concentrations of separation gel and spacer gel were 12% and 5%, respectively; the electrophoresis voltage for separation gel was 180 V, and the electrophoresis time was 300 min; the sample loading amount and concentration were 16 μL and 0.5 μg/μL samples, respectively; the gel was stained with modified Coomassie brilliant blue for 12 h and then decolorized for 12 h. Within 0-12 h of fermentation, the koumiss whey protein contents increased and peaked （5.12 μg/μL） at 12 h, and then fell with the extension of fermentation time, decreasing to 3.92 μg/μL at 96 h of fermentation. SDS-PAGE analysis showed that a total of 13 effective bands of whey protein within the molecular weight range of 10-70 kDa were observed. During the fermentation process, the contents of 3 types of whey protein, β-lactoglobulin, lysozyme C, and α-lactalbumin, fluctuated to varying degrees. The sum of their contents peaked at 72 h of fermentation, accounting for 85.73% of the total whey protein contents and maintained high levels during the fermentation process. It was indicated that they were the main components of whey protein in traditional koumiss within the fermentation process of 96 h. Among them, the content of β-lactoglobulin was the highest, accounting for an average of 38.92% of the total whey protein contents. The content of casein with the molecular weight range of 20-40 kDa began to decrease after 24 h of fermentation, and the corresponding bands disappeared till 60 h. The protein with a molecular weight of 10.33 kDa was depleted within 12 h of fermentation and reappeared at 60 h, and its content gradually increased with the extension of fermentation time and peaked at 84 h, accounting for 9.84% of the total whey protein contents. The protein with a molecular weight of 49.80 kDa began to appear after 72 h of fermentation, and its content reached 4.11% of the total whey protein contents at 96 h. Compared to the other whey protein components, the content of β-lactoglobulin and immunoglobulin had minor changes during the fermentation process. [Conclusion] The whey protein contents with the molecular weight range of 10-70 kDa in traditional koumiss from Inner Mongolia had regular increase and decrease within 96 h of fermentation. The main protein that was digested and decomposed was casein. There were some differences in the composition and content of whey protein in different fermentation stages of koumiss, while the original main components β-lactoglobulin, lysozyme C, and α-lactalbumin maintained higher levels. From the middle stage of fermentation, the proportion of peptides with relatively small molecular weight （10.33 kDa） in the whey protein of koumiss gradually increased. Our results showed that the traditional koumiss not only retained the original nutritional value of whey protein in mare milk, but also added some easily absorbed small molecular weight proteins through fermentation.

Key words: koumiss, traditional fermentation, whey protein, SDS-PAGE, Inner Mongolia