Seasonal Changes in the Protein Composition of Khainak Milk

Abstract

The qualitative composition of commercial milk is a relevant issue of the food industry. The khainak, or yattle, is a hybrid between the yak and domestic cattle. The research objective was to study the seasonal protein composition of khainak milk from the Northern Kyrgyzstan highlands. The study featured samples of khainak milk obtained from farms located in the Issyk-Kul region at an altitude of 2840 m above sea level. Standard research methods included high pressure liq uid chromatography and capillary electrophoresis. Khainak milk has more protein than cow milk, and the mass fraction of protein in it is 3.91–4.39%. In this research, the mass fraction of protein in khainak milk obtained in spring, summer, and autumn exceeded that of cow milk by 0.54, 1.02, and 0.84%, respectively. The total nitrogen content correlated with the mass fraction of protein, i.e., it was at its highest in summer (0.689 ± 0.004%). The content of non-protein nitrogen remained almost the same (0.0489–0.0496%). Spring milk contained by 0.2% more whey protein than summer milk (0.94 ± 0.05%) and autumn milk (0.97 ± 0.05%). Summer milk demonstrated a 1% increase in casein proteins, compared to spring and autumn samples. The average β-lactoglobulin content was 2.35 mg·mL–1, while α-lactoalbumin was 2.12 mg·mL–1 of the total albumin fraction. In terms of amino acid composition, khainak milk was balanced except for tryptophan. In the warm season, the content of essential amino acids was higher than in the cold season, which corresponded to the changes in total protein co ntent. Khainak milk is richer in protein and some other components than cow milk, which makes it a valuable non-traditional dairy raw material for such protein products as cheese or cottage che ese, including their functional variants.

Keywords

• milk
• khainak
• season
• protein content
• non-protein nitrogen
• whey protein
• amino acids