不同部位牦牛肉氨基酸、脂肪酸含量分析与营养价值评价

为明确不同部位牦牛肉氨基酸、脂肪酸等营养物质含量，采集西藏那曲牦牛的上脑、里脊、外脊、米龙、臀肉、腱子肉、腹肉、肩肉及胸肉9 个部位分割肉，测定其蛋白质、脂肪、灰分、氨基酸和脂肪酸组成。结果表明：不同部位牦牛肉的蛋白质含量为19.30%～24.20%，其中腹肉中蛋白质含量最低，外脊中最高；脂肪含量为1.03%～22.47%，腹肉中脂肪含量显著高于其他各部位，米龙、外脊、臀肉和肩肉中脂肪含量较低，不足1.5%。在测定的18 种氨基酸中，谷氨酸含量最高，其次是赖氨酸、天冬氨酸、亮氨酸和精氨酸；腹肉中氨基酸含量显著低于其他部位（P＜0.05），9 个不同部位牦牛肉中必需氨基酸占总氨基酸的比例为39.03%～40.00%，与联合国粮农组织/世界卫生组织的推荐值接近；里脊和外脊能够满足所有膳食氨基酸需要，上脑、米龙、臀肉、腱子肉、腹肉、肩肉及胸肉中，缬氨酸是限制性氨基酸。脂肪酸总量由大到小为腹肉＞上脑＞里脊＞臀肉＞外脊＞胸肉＞肩肉＞腱子肉＞米龙，油酸、棕榈酸和硬脂酸是牦牛肉中主要的脂肪酸，二十二碳六烯酸、二十碳五烯酸等n-3脂肪酸含量较少，n-6/n-3比值高于膳食推荐值。以常规营养组分、氨基酸组成和脂肪酸组成分别进行聚类分析，总体可分为腹肉、上脑与其他部位肉三大类。综上所述，不同部位牦牛肉中蛋白质、脂肪、氨基酸及脂肪酸等营养物质含量存在差异。

Amino Acid and Fatty Acid Composition and Nutritional Value Evaluation of Different Yak Meat Cuts

In order to determine the profiles of amino acids and fatty acids in different cuts of Tibetan yak meat, nine meat cuts including chuck, tenderloin, sirloin, topside, rump, shank, belly, shoulder, brisket were collected from yak carcasses for the measurement of protein content, fat content, ash content, amino acid and fatty acid composition. The results showed that protein contents of all cuts of yak meat ranged from 19.30% to 24.20%; the highest and lowest values were found in sirloin and belly, respectively. Fat contents ranged from 1.03% to 22.47%, significantly higher in belly was than in other parts (P < 0.05); topside, striploin, rump and shoulder contained low contents of fat (less than 1.5%). Among the 18 amino acids determined, glutamic acid was the most abundant, followed by lysine, aspartic acid, leucine and arginine. The content of amino acids in belly was significantly lower than that in other parts (P < 0.05). The proportion of essential amino acids to total amino acids in 9 different parts of yak beef ranged from 39.03% to 40.00%, which was close to the FAO/WHO recommended value. Loin and sirloin met the dietary need for amino acids. Valine was the limiting amino acid in chuck, topside, rump, shank, belly, shoulder and brisket. Total fatty acid contents of different meat cuts were in the following decreasing order: belly > chuck > tenderloin > rump > sirloin > brisket > shoulder > shank > topside. Oleic acid, palmitic acid and stearic acid were the major fatty acids in yak meat with lesser amounts of docosahexenoic acid, eicosapentaenoic acid and other n-3 fatty acids. Cluster analysis classified these 9 meat cuts into three categories: belly, chuck and other parts based on nutrient, amino acid and fatty acid composition. Overall, we concluded that the contents of protein, fat, amino acid, fatty acid and other nutrients in different parts of yak beef were different. These results can provide a theoretical basis for developing yak meat with high nutritional value and for healthy consumption.