Feasibility of Casein to Record Stable Isotopic Variation of Cow Milk in New Zealand

Abstract

Dairy products occupy a special place among foods in contributing to a major part of our nutritional requirements, while also being prone to fraud. Hence, the verification of the authenticity of dairy products is of prime importance. Multiple stable isotopic studies have been undertaken that demonstrate the efficacy of this approach for the authentication of foodstuffs. However, the authentication of dairy products for geographic origin has been a challenge due to the complex interactions of geological and climatic drivers. This study applies stable isotope measurements of δ2H, δ18O, δ13C and δ15N values from casein to investigate the inherent geo-climatic variation across dairy farms from the South and North Islands of New Zealand. The stable isotopic ratios were measured for casein samples which had been separated from freeze-dried whole milk samples. As uniform feeding and fertilizer practices were applied throughout the sampling period, the subtropical (North Island) and temperate (South Island) climates were reflected in the variation of δ13C and δ15N. However, highly correlated δ2H and δ18O (r = 0.62, p = 6.64 × 10−10, α = 0.05) values did not differentiate climatic variation between Islands, but rather topographical locations. The highlight was the strong influence of δ15N towards explaining climatic variability, which could be important for further discussion.

Keywords

• stable isotopes
• cow milk
• <i>δ</i>¹⁵N signature
• casein
• climatic variables
• IRMS