College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, Zhejiang, China.
Department of Food Science, University of Wisconsin-Madison 53706.
J Dairy Sci. 2021 Aug;104(8):8661-8672. doi: 10.3168/jds.2021-20269. Epub 2021 May 28.
Yak milk is an essential and predominant food resource for Tibetan people for subsistence purposes and to combat altitude-induced challenges. Due to its unique qualities, yak milk has recently been gaining broader attention from consumers across China as well in other parts of the world. One of the key characteristics of yak milk is the protein content, which is about 40 to 60% higher than that of native bovine milk. In this work, a sensitive and reproducible high-throughput analytical method was developed employing both ultra high-performance liquid chromatography Orbitrap (Thermo Fisher Scientific) high-resolution accurate mass spectroscopy (UHPLC-HRAM-MS) and UHPLC coupled with triple quadrupole tandem MS (UHPLC-QqQ-MS) to simultaneously analyze 8 milk proteins. A total of 15 Maiwa yak milk samples and 15 bovine milk samples were qualitatively and quantitatively analyzed using targeted proteomics and compared for α-lactalbumin, β-lactoglobulin, α-casein, α-casein, β-casein, κ-casein, lactoferrin, and osteopontin. Peptides of β-lactoglobulin were used to specifically distinguish yak and bovine milk. The results showed that this novel detection method could quantitatively detect these major and minor milk proteins with >0.99 linear correlation coefficient and a recovery rate between 90 and 120%, with relative standard deviations typically less than 10%. The data revealed that yak milk not only had higher overall milk protein content than bovine milk but higher lactoferrin and osteopontin contents as well. The lactoferrin content of yak milk was about 30% higher than that of bovine milk, and the osteopontin content of yak milk was nearly twice that of bovine milk. The application of this method demonstrates that UHPLC-HRAM-MS and UHPLC-QqQ-MS are suitable for high-throughput qualitative and quantitative analysis of major and minor proteins of yak and bovine milk.
牦牛奶是藏民维持生计和应对高原挑战的主要食物来源。由于其独特的性质，牦牛奶最近在中国乃至世界其他地区受到了更广泛的消费者关注。牦牛奶的一个关键特点是蛋白质含量，比本地牛奶高 40%到 60%。在这项工作中，开发了一种灵敏且可重现的高通量分析方法，采用超高效液相色谱-轨道阱（Thermo Fisher Scientific）高分辨率精确质量谱（UHPLC-HRAM-MS）和超高效液相色谱-三重四极杆串联质谱（UHPLC-QqQ-MS）同时分析 8 种乳蛋白。使用靶向蛋白质组学对 15 份麦洼牦牛奶样品和 15 份牛奶样品进行定性和定量分析，并比较了α-乳白蛋白、β-乳球蛋白、α-酪蛋白、α-酪蛋白、β-酪蛋白、κ-酪蛋白、乳铁蛋白和骨桥蛋白。β-乳球蛋白的肽段被用来特异性地区分牦牛和牛奶。结果表明，这种新的检测方法可以定量检测这些主要和次要的乳蛋白，其线性相关系数大于 0.99，回收率在 90%到 120%之间，相对标准偏差通常小于 10%。数据显示，牦牛奶不仅总乳蛋白含量高于牛奶，而且乳铁蛋白和骨桥蛋白含量也更高。牦牛奶中的乳铁蛋白含量比牛奶高约 30%，而牦牛奶中的骨桥蛋白含量几乎是牛奶的两倍。该方法的应用表明，UHPLC-HRAM-MS 和 UHPLC-QqQ-MS 适用于牦牛奶和牛奶中主要和次要蛋白的高通量定性和定量分析。
