Department of Chemistry, Life Sciences, and Environmental Sustainability, Parco area delle Scienze 157/A, University of Parma, Parma, Italy.
Department of Environmental Sciences, Jožef Stefan Institute, Ljubljana, Slovenia.
Rapid Commun Mass Spectrom. 2021 Nov 30;35(22):e9160. doi: 10.1002/rcm.9160.
The oxygen and hydrogen isotope compositions of the water component of the milk from nine Italian dairy farms were studied together with the farm water for one year. The aim was to verify the importance of farm water and seasonal temperature variation on milk isotope values and propose mathematical relations as new tools to identify the milk origin.
Milk was centrifuged to separate the solids and then distilled under vacuum to separate water. δ( O/ O) and δ( H/ H) analyses of the water molecules were carried out using a water equilibrator online with a mass spectrometer. For oxygen and hydrogen isotope determination, water was equilibrated with pure CO for 7.5 h and with pure H for 5 h, respectively. The isotope ratio value is indicated with δ (expressed on the VSMOW/SLAP scale) as defined by IUPAC.
The average annual isotope value of milk at the different cattle sheds is mostly related to the farm water suggesting that the drinking water is the most important factor influencing the isotopic values of the milk water. The milk/water fractionation factor correlates with the milking time and, thus, the seasonal temperature is best described by a 4 order polynomial regression line. A two-level check model was used to verify the milking provenance.
This study shows that it is essential to analyze both milk and farm water to indicate provenance. A two-step verification tool, based on the difference between the measured and calculated δ( O/ O) values, and the difference between the calculated and estimated milk-water fractionation factors, allowed the source determination of milk. Both conditions must be met if the milk is considered to be from the Parmigiano-Reggiano production region. Although this approach was developed for this region, it can easily be tested and adapted to other dairy production areas.
研究了意大利 9 个奶牛场的牛奶中水分的氧和氢同位素组成，以及一年中奶牛场用水的情况。目的是验证奶牛场用水和季节温度变化对牛奶同位素值的重要性，并提出数学关系作为识别牛奶来源的新工具。
将牛奶离心分离出固体，然后在真空中蒸馏分离出水。使用与质谱仪在线连接的水平衡器对水分子的 δ( O/ O)和 δ( H/ H)进行分析。为了测定氧和氢同位素，水分别与纯 CO 平衡 7.5 h 和纯 H 平衡 5 h。同位素比值用 δ（用 IUPAC 定义的 VSMOW/SLAP 标度表示）表示。
不同牛棚的牛奶平均年同位素值主要与农场用水有关，这表明饮用水是影响牛奶水同位素值的最重要因素。牛奶/水分馏因子与挤奶时间相关，因此，季节性温度最好用 4 阶多项式回归线来描述。使用两级检查模型来验证挤奶来源。
本研究表明，分析牛奶和农场用水对于指示来源至关重要。基于测量和计算的 δ( O/ O)值之间的差异以及计算和估计的牛奶-水分馏因子之间的差异的两步验证工具，允许确定牛奶的来源。如果牛奶被认为来自 Parmigiano-Reggiano 生产地区，则必须满足这两个条件。尽管这种方法是针对该地区开发的，但它可以很容易地在其他乳制品生产地区进行测试和改编。
