Correlation between precipitation and geographical location of the δ~2H values of the fatty acids in milk and bulk milk powder

摘要

Hydrogen isotope ratios (δ~2H) have become a tool for food traceability and authentication of agricultural products. The principle is that the isotopic composition of the produce is influenced by environmental and biological factors and hence exhibits a spatial differentiation of δ~2H. This study investigates the variation in δ~2H values of New Zealand milk, both in the bulk powder and individual fatty acids extracted from milk samples from dairy factories across New Zealand. Multivariate statistical analyses were used to test for relationships between δ~2H of bulk milk powder, milk fatty acid and geographical location. Milk powder samples from different regions of New Zealand were found to exhibit patterns in isotopic composition similar to the corresponding regional precipitation associated with their origin.A model of δ~2H in precipitation was developed based on measurements between 2007 and 2010 at 51 stations across New Zealand (Frew and Van Hale, 2011). The model uses multiple linear regressions to predict daily δ~2H from 2 geographic and 5 rain-weighted climate variables from the 5×5km New Zealand Virtual Climate Station Network (VCSN). To approximate collection radius for a drying facility the modelled values were aggregated within a 50km radius of each dairy factory and compared to observed δ~2H values of precipitation and bulk milk powder. Daily δ~2H predictions for the period from August to December for the area surrounding the sample collection sites were highly correlated with the δ~2H values of bulk milk powder. Therefore the δ~2H value of milk fatty acids demonstrates promise as a tool for determining the provenance of milk powders and products where milk powder is an ingredient. Separation of milk powder origin to geographic sub-regions within New Zealand was achieved. Hydrogen isotope measurements could be used to complement traditional tracking systems in verifying point of origin.