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

• Main Authors: Kavindra Wijenayake, Russell Frew, Kiri McComb, Robert Van Hale, Dianne Clarke
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Molecules
• Subjects: stable isotopes; cow milk; <i>d</i>¹⁵N signature; casein; climatic variables; IRMS
• Online Access: https://www.mdpi.com/1420-3049/25/16/3658

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 <i>d</i>²H, <i>d</i>¹⁸O, <i>d</i>¹³C and <i>d</i>¹⁵N 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 <i>d</i>¹³C and <i>d</i>¹⁵N. However, highly correlated <i>d</i>²H and <i>d</i>¹⁸O (r = 0.62, p = 6.64 × 10⁻¹⁰, a = 0.05) values did not differentiate climatic variation between Islands, but rather topographical locations. The highlight was the strong influence of d¹⁵N towards explaining climatic variability, which could be important for further discussion.