h altitudes is richer in PUFA, namely CLA. As such, the resulting cheese and dairy products will have value-added nutraceutical functions.

Yak milk casein has been hydrolyzed to generate antihypertensive peptides, such as YQKFPQY (αs2-CN; f89-95), LPQNIPPL (β-CN; f70-77), SKVLPVPQK (β- CN; f168-176), LPYPYY (κ-CN; f56-61) and FLPYPYY (κ-CN; f55-61), and two novel ACE-inhibiting peptides [33,34]. These peptides are multifunctional bioactives with potential use for producing value-added functional foods and proteins [34]. Compared to cow milk fat, n-3 PUFA in yak milk fat is extremely higher (e.g., 3.2 times) [35]. The n-3 PUFA to n-6 PUFA ratio in yak cheese was 0.87, but only 0.20 in cow cheese. Based on the minimum healthy set ratio of >0.25 [36], yak cheese is considered a highly healthy food for humans. Greater CLA cis-9, trans-11 relative to cow cheese suggests more anticarcinogenic effects of yak cheese and dairy products. The amounts of CLA cis-9, trans-11 and CLA trans-11- C18:1 in yak cheese have been found to be respectively 4.2 and 4.6 times greater than that in cow cheese [33]. Research data indicate that considerable amount of CLA cis-9, trans-11 originates directly from the rumen. To supply adequate amount of CLA cis-9, trans-11, inclusion of 100 g yak cheese in daily human diets should suffice [33].

The milk yield of yak and its hybrid, “khainag”, is 300 and 470 kg, respectively. The larger diameter of fat globule (5 to 6 μm) eases butter separation in yak milk, thus being suitable for milk cream making. Due to high carotene content, its butter is yellowish and quite delicious. Along with high proteins, yak milk has high acidity. Saturated and unsaturated FA comprise respectively 22% and 55.2% of total fat, with greater content of low molecular weight volatile acids, compared to cow milk [37]. Mongolians produce from yak milk butter as well as fermented and protein products. Butter products include milk membrane (orom), and yellow and white butter. The fermented products include yoghurt and koumiss (airag). Wet and dried curds (aaruul) are among protein products. Yak milk has greater contents of total proteins (4.6% - 5.8%), total casein (4.0%) and individual caseins than cow milk. The higher β-casein (45%) and the lower α-s-casein (40%) along with somewhat higher κ-casein (15%) make yak milk a favorable food for infants as traditionally consumed by Tibetan nomads [37]. Yak milk’s whey proteins, β-lactoglobulin and serum albumin compositions are rather similar to homologous cow whey proteins. Nonetheless, more research is needed to figure out how to optimize yak milk utilization in humans of extreme climatic environ-ments.

China may be the largest producer of naturally fermented yak milk called “kurut”. Kurut is an important food for people of Qinghai [38]. Kurut includes products produced by natural fermentation of yak milk in a specially treated big jar for at least 7 - 8 days at 10˚C - 15˚C. These conditions generate enough acid, alcohol and flavor. A common property of kurut is the presence of alcohol and lactic acid. Kurut is almost known in all regions of Qinghai as an indigenous fermented milk product with economic and nutritional importance to the people of Qinghai [39]. Kurut is rich in casein, immunoglobulins, serum albumin, β-lactoglobulin, α-lactalbumin, and two unknown fractions [40,41]. Kurut contains greater numbers of lactic acid bacteria and yeast than other traditional fermented milks (lactic acid bacteria counts of 9.18 ± 0.851 log cfu/ml; yeast counts of 8.33 ± 0.624 log cfu/ml) [40].

4. Conclusions and Implications

Milk is the most functional natural liquid because it 1) is produced from the most abundant, least digestible nutrients and 2) generously hosts numerous bioactives that function beyond calculated nutritional values. Camel milk contains less short-chain FA than cow, sheep and buffalo milks, and has about 3 times greater vitamin-C than cow milk. One kg camel milk meets 100% of daily human requirements for calcium and phosphorus, 57.6% for potassium, 40% for iron, copper, zinc and magnesium, and 24% for sodium. Camel milk has long been used to treat liver problems, lower bilirubin output, reduce vitamin inadequacy and nutrient deficiency, and boost immunity. Camel milk reduces food allergies caused by cow milk and milk products. Camel milk has low milk fat content with increased PUFA proportions. Camel milk lacks β-lactoglobulin and is rich in immunoglobulins, thus being compatible with human milk. Yak milk has greater solids, protein and fat, and is richer in PUFA and casein than cow milk. Yak cheese has about 4 times more CLA than Canadian cheddar. Yak milk casein has been hydrolyzed to produce antihypertensive peptides with multiple bioactive functions and capacities for producing value-added functional foods and proteins. More research is needed to further characterize biophysical and biochemical properties of camel and yak milks as functional substitutes for cow milk and other animal products. Persistent education and data dissemination will be a commitment for such milk natural health implications to be optimally perceived by science and public communities worldwide.

5. Acknowledgements

The Ministry of Science, Research and Technology (Tehran, Iran) and University of Zanjan (Iran) are thankfully acknowledged for supporting the author’s programs of optimizing science education in the new millennium.

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