Yalan Li, Xiaoting Yang, Shilin Zhao, Pengcuo Zhaxi, Song Qu, Yan Zhao*

Food Control；2026

Abstract:

Hongyuan yak milk (HYM) is the first dairy product in China to be granted protected geographical indication (PGI) certification, requiring effective traceability methods to ensure authenticity. Stable isotope ratio analysis (SIRA) is a powerful tool for this purpose. However, its application is often hindered by sampling strategies that do not fully account for the spatiotemporal and ecological influences on isotope fractionation. Over three consecutive years (2021-2023), we analyzed carbon stable isotope (δ¹³C) in different HYM components (milk, fat, casein, whey), and evaluate the effects of temporal (year, month, date), spatial (township), and eco-environmental (forage, soil, climate) factors. In temporal dimensions, annual variation dominated δ¹³C values, explaining up to 64.12% of variances, and surpassing the effects of monthly and daily variations. The components of milk and fat showed no significant differences across sampling months or dates. Within PGI production area, δ¹³C for milk, fat, and casein showed no significant spatial variation, except for whey. Furthermore, forage δ¹³C is significantly correlated with HYM components and exhibits consistent spatiotemporal variations, serving as a direct factor. Meteorological conditions exerted an indirect influence by altering forage. This study established a scientific sampling strategy for PGI HYM traceability. Annual sampling using stable components (milk or fat) was conducted at a fixed location within the PGI production region on any date during the lactation period between July and September. The strategy captures critical temporal variation while minimizing sampling workload, providing an economical and reliable method for SIRA applications and serving as a reference for other PGI products.