饲料对牛乳的碳稳定同位素比值的影响

通过等电点沉淀与离心分离牛乳中的酪蛋白和脂肪，采用元素分析 串联稳定同位素比值质谱法（EA-IRMS）测定牛乳组分的δ¹³C值。经验证，该方法具有良好的准确性和重复性，牛乳及其各组分δ¹³C值测定精度标准偏差（SD）均小于0.1‰（n=5）。对不同牛乳中δ¹³C值进行比较表明，饲料组成直接影响牛乳中的碳稳定同位素组成。以玉米为主要饲料的奶源地牛乳中δ¹³C值均高于-17.6‰，若饲料中含有羊草和苜蓿会使牛乳的δ¹³C值相对偏负。购自不同地区的市售乳样品δ¹³C值具有不同特点,中国市售乳样品的δ¹³C值与一些发达国家样品的δ¹³C值具有显著差异。研究结论验证了牛乳δ¹³C值在牛乳溯源中的作用，为稳定同位素分析技术在牛乳真实性溯源的应用积累了数据与理论基础。

The Impact of Forage on the Stable Carbon Isotope Composition in Milk

The stable carbon isotope (δ¹³C) ratios of whole milk and its isolated components (casein, skim milk, and fat) were determined by elemental analysis-isotoperatio mass spectrometry (EA-IRMS). This technique was found to be repeatable and possess good accuracy with a standard deviation of less than 0.1‰ (n=5). A comparison of the δ¹³C values of different milk samples indicates that the δ¹³C composition is impacted by the type of forage consumed by the cows. The δ¹³C values of milk from farms in which maize is the main roughage are higher than -17.6‰, are relatively lower when the diet contains Leymus chinensis and alfalfa. The δ¹³C values of commercially available milk purchased from different regions demonstrate distinct characteristics, milk samples from China and countries using advanced animal husbandry practices are significant differences. The conclusion of this research verified δ¹³C values in terms of tracing the types of milk and producing areas. The accumulated data was used to lay a theoretical foundation for the application of stable isotope analysis techniques in milk traceability.