Antioxidant Property Of Alpine Plants And Yak Milk On Qinghai-tibetan Plateau

The Qinghai-Tibetan plateau, the highest and largest plateau in the world, extends over 1.29 × 108 ha, accounting for one-third of the total grasslands in China. The area is known for its extremely harsh environment, being characterized by severe cold, hypoxia and strong ultraviolet radiation. The extremely harsh environment on the Qinghai-Tibetan Plateau is associated with high oxidative stress to the organisims. Furthermore, nutrition deficiency and physical activity exacerbate the extent of this stress. Animals could respond to oxidative stress by reducing physical activity and/or by increasing intake of dietary antioxidants. On the one hand, nutrion intake could depress the formation of free radicals, on the other hand, increase of antioxidants intake could repair free radical injury. Due to geographical location and unique culture, dietary of Tibetan pastoralists is tedious. They mainly live on highlandbarley and animal devired food such as Tibetan sheep and yak meat, milk, yoghourt, butter. From food chain approach, plant-animal-people, this study determined antioxiants and total antioxidant activity of alpine forage and yak milk on Qinghai-Tibetan to reveal the nutrition mechanism for forage, yak and pastoralists to adapt to the hostile environment, and dietary survey was conducted among Tibetan pastoralists to find out how would their dietary pattern chages affect their nutrion intake. The results are as follows:(1)Composition and total antioxidant capacities of 5 alpine plants growing at different altitudes on the Qinghai-Tibetan plateau. 5 plant species found at three altitudes: 3016 m, 3814 m and 4621 m on the Qinghai-Tibetan plateau was selected including one sedge, Kobresia tibetica; two forbs, Polygonum viviparum and Oxytropis ochrocephala; two forbs,Potentilla fruticosa and Salix oritrepha. Protein and fats in the five alpine plants generally increased with altitude while mineral content decreased. The Trolox equivalent antioxidant capacity increased with altitude in all plants(P<0.05), total phenols and tannins generally increased with altitude, the difference was not significant(P>0.05)except for Oxytropis ochrocephala and Potentilla fruticosa, polyunsaturated fatty acids, Monounsaturated fatty acids, linoleic acid and linolenic acid all increased with increasing altitudes(P<0.05), they all provide materials for yaks to produce products rich in functional nutrition especially for n-3 polyunsaturated fatty acids.(2) Composition and total antioxidant capacities of 18 alpine plants growing at different altitudes on the Qinghai-Tibetan plateau. Samples of 18 species were selected including 4 sedges, Kobresia tibetica, Kobresia humilis, Kobresia capillifolia and Kobresia royleana; 5 grasses, Elymus.nutans, Koeleria litwinowii, Poa pratensis, Helictotrichon tibeticum and Stipa breviflora; 5 forbs, Polygonum viviparum, Gentiana macrophylla, Iris lactea, Equisetum arvense and Oxytropis ochrocephala; 4 shrubs, Potentilla fruticosa, Salix oritrepha, Caragana jubata, Caragana brevifolia. Concentration of CP in 18 alpine plants ranged from 9.1 to 25.2 g/100 g DM with Potentilla fruticosa and Caragana brevifolia, both shrubs, having the lowest and highest concentrations, respectively. Average ash content of all 18 plants was 6.94 g/100 g DM, Studies at Wushaoling showed that concentrations of the minerals Ca, P, K, Mg, Cu, Fe, Mn, Zn in forage in July met the dietary requirements for yaks, except for Na which was considerably lower than requirements according to NRC. The fatty acids, α-linolenic acid(cis-9,cis-12, cis-15 C18:3), linoleic acid(cis-9, cis-12 C18:2), and palmitic acid(C16:0) composed ~83% of total fatty acids in the alpine plants. In general, sedges and grasses had higher PUFA contents than forbs and shrubs. The higher proportion of polyunsaturated fatty acids at higher elevations is a precursor to synthesis of conjugated linoleic acid and n-3 polyunsaturated fatty acids. Kobresia tibetica has low antioxidant activity and the other three sedges were classified as having medium level of Trolox Equivalent antioxidant capacity. In contrast, three of the four shrubs expect for Caragana brevifolia having high levels of antioxidants. Yet, the sedges are most consumed by yaks, nearly occupies 64% of DM intake of yaks, while shrubs are browsed when other forage is scarce. It should be noted that plants increase in nutritional value with altitude, including in antioxidant capacity, and it is conceivable that the antioxidant capacity in the high altitude in July and August, sedges was adequate for yaks.(3)Composition and total antioxidant activity of the milk of yaks raised at different altitudes on the Qinghai-Tibetan Plateau. Three sites on the mid-eastern part of the Qinghai-Tibetan Plateau were selected for the study: Wushaoling(37° 12’ 02 " N and 102° 51’ 38" E, altitude 3016 m), Tianzhu Tibetan Autonomous County, Gansu Province; Dawuzhen(34° 27’ 37 " N and 100° 12’ 35" E, altitude 3824 m), Guoluo Tibetan Autonomous Prefecture, Qinghai Province; and Gulu(30° 58’ 87 " N and 91° 37’ 39" E, altitude 4750m), Nagqu Prefecture, Tibet Autonomous Region. Twenty healthy, multiparous females(aged between 7 and 11 years, body weight from 250kg-280 kg, at the same lactating period) were selected at each altitude. We choose yaks which were managed under similar conditions at each altitude and were not offered any food supplements. The animals were of similar age, parity, time of lactation and health status to minimize these factors on milk composition. We found that the TEAC, vitamin A concentration, fat content, conjugated linoleic acid, γ-linolenic acid, total unsaturated fatty acids, and Fe, Zn and Na concentrations of yak milk increased(P<0.05)while vitamin C concentration, crude protein content and Cu and Mn concentrations decreased with increasing altitude(P<0.05). Also, the atherogenic index was lower at the middle and highest altitudes than at the lowest altitude(P<0.05). Thus, in general, there was an increase in nutritional value in the milk with altitude, and nutritional value of yak milk was significantly higher than commercial milk.(4) With the prosperity development of social economy, diet of pastoralists has undergone tremendous change. Yak milk and dairy consumption has decreased, compared with sedentarized pastoralists in 1986, the milk consumption had reduced by 2/3; for economic consideration, pastoralists would like to sell yak milk and buy commercial milk and dairy products for daily consumption. All of them decreased pastoralists’ functional nutrient intake, while we also found that their vegetable consumption increased. So, How would this kind of changes in dietary affect pastoralists’ health in the future, it should be attracted more attention from researchers.