Investigating the Region-of-Origin of American Milk Using Stable Isotope Analysis

CHESSON, LESLEY A; O'GRADY, SHANNON P; VALENZUELA, LUCIANO O; CERLING, THURE E; EHLERINGER, JAMES R

Simposio; Food Safety and Nutrition: Methods and Systems for Tracking, Tracing and Verifying Foods; 2009

Science Laboratory (CSL)/Joint Institute for Food Safety and Applied Nutrition (JIFSAN) Joint Symposium

Americans dine at a continental table, consuming foods and beverages produced in non-local (to the consumer) regions of the USA. The complexity of the distribution systems used in the modern human food chain presents unique challenges to food tracking and authentication. Recent advances in stable isotope analysis at natural abundance levels make it possible to investigate the region-of-origin claims of many food and fiber items. The stable isotope ratios of hydrogen (δ2H) and oxygen (δ18O) within the global water cycle vary across continents, with decreasing values from low-latitude, low-elevation coastal regions towards inland, high-latitude mountainous areas. Because plants and animals incorporate local water isotopes, stable isotope analysis can provide quantitative information about the region-of-origin of different food items.Milk is an example of a food with widespread and multiple origins within the USA. The ability to determine the region-of-origin for milk and other dairy products would be an indispensable tool for today s food industry. To explore links between a dairy product s purchase location and region-of-origin, we collected milk from 26 outlets of a national chain fast food restaurant located in 17 states in the USA. We also purchased milk from a traditional grocery retailer (supermarket) in these same cities. Water extracted from the milk was analyzed for its δ2H and δ18O values. Additionally, we collected and analyzed tap water samples from each city.The δ2H values of water extracted from restaurant milk ranged from -107 to -27 and δ18O values ranged from -13.2 to -4.0 . Both δ2H and δ18O values of water extracted from restaurant milk samples were positively correlated with local tap water (r2= 0.29 and P<0.01; r2= 0.28 and P<0.01, respectively). We observed three distinct groups within the restaurant milk data set. The group with the lowest mean δ2H and δ18O water values (-105 ± 1 and -12.9 ± 0.2 , respectively) was comprised of samples collected in interior states (e.g., NV, UT, and WY) where we also measured low tap water values. The group with the highest mean δ2H and δ18O extracted water values (-31 ± 3.4 and -4.7 ± 0.4 , respectively) included samples collected in TX and east coast states, where tap water values were also high.In contrast, water extracted from supermarket milk had δ2H values that ranged from -102 to -16 , while δ18O values ranged from -12.3 to -3.6 . Stable isotopes of water extracted from the supermarket milk samples were also positively correlated with local tap water (r2= 0.63 and P < 0.0001 for H; r2= 0.56 and P<0.0001 for O). Similar to the restaurant samples, the lowest δ2H and δ18O extracted water values were measured from a milk sample collected in WY, where we collected tap water samples with low δ2H and δ18O values. The highest δ2H and δ18O extracted water values were from a sample collected in TX, where we also measured high tap water values.