Summary of reference materials for the determination of the nutrient composition of foods

Abstract

Certified reference materials (CRMs) play a critical role in validating the accuracy of nutrient data for food samples. A number of available food CRMs of dif- fering matrix composition have assigned concentrations for various nutrients, along with associated uncertainty inter- vals (UIs) for those values. These CRMs have been used extensively in the United States Department of Agricul- ture's (USDA) ongoing National Food and Nutrient Anal- ysis Program (NFNAP) to monitor the accuracy of assays of key foods and nutrients consumed in the United States. A total of 690 assigned values for individual nutrients, including proximates, vitamins, macroelements, microele- ments, fatty acids, amino acids, and selected phytochemi- cals (e.g., carotenoids), were compiled from the certificates of analysis for 63 CRMs, and the specified UI in each case was expressed as a percentage of the assigned certified or reference concentration. Across all nutrients, 63.5% of the UIs were less than 10% of the assigned value, 25.5% were 10-20%, and 11% were greater than 20% of the assigned value. The UIs for proximates, minerals, and trace elements were most consistently less than 10% of the assigned value. The relative uncertainties were significantly higher for vitamins, suggesting greater challenges in measuring and certifying these components. These high UIs (greater than 10% assigned value) in the best available reference mate- rials are likely to be indicative of the precision and accu- racy that can be obtained by current measurement systems for these components. These data suggest that care must be taken in choosing CRMs to monitor food composition analysis, including evaluating what levels of uncertainty are required in assigned values and which analytical mea- surement systems for food components need closer exam- ination and improvement.