DEVELOPMENT OF ANALYTICAL METHODS FOR TRACE ELEMENTS AND ELEMENTAL SPECIES IN FOODS
Location: Food Composition and Methods Development Lab
Title: FLAVONOID CONTENT OF U.S. FRUITS, VEGETABLES, AND NUTS.
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2006
Publication Date: December 20, 2006
Citation: Harnly, J.M., Doherty, R.F., Beecher, G.R., Holden, J.M., Haytowitz, D.B., Bhagwat, S.A., Gebhardt, S.E. 2006. Flavonoid content of U.S. fruits, vegetables, and nuts. Journal of Agricultural and Food Chemistry. 54:966-9977.
Interpretive Summary: Flavonoids comprise a large family of compounds that are found in every fruit, vegetable, and nut that we eat. They are reported to have health protective benefits. Research to clearly identify these benefits requires the establishment of a database that provides the concentration of flavonoids in a wide variety of foods. Samples were collected systematically across the country so that the database would be an accurate representation of the U.S. foods. We analyzed 20 flavonoid compounds in more than 60 fresh fruits, vegetables, and nuts. The average values of flavonoids measured in foods by this study compared well to data previously collected in the U.S. National Nutrient Database for Standard Reference. This study also showed that the concentration of flavonoids in foods, as consumed by the U.S. public, is highly variable. This is most likely due to different cultivars, local growing conditions, and processing methods. This database represents the first comprehensive investigation of the flavonoid content of U.S. foods. This data is essential to research on the relationship between flavonoids and good health.
Analytical data are reported for 20 flavonoids (as aglycones) determined for more than 60 fresh fruits, vegetables, and nuts collected from four regions across the U.S at two times of the year. Sample collection was designed and implemented by the Nutrient Data Laboratory (USDA). Analyses of 8 flavan-3-ols (catechin, catechin gallate, epicatechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate, gallocatechin, and gallocatechin gallate), 6 anthocyanins (cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin), 2 flavanones (hesperitin and naringenin), 2 flavones (apigenin and luteolin), and 2 flavonols (myricetin and quercetin) were performed by the Food Composition Laboratory (USDA) using a hydrolysis method for the anthocyanidins, flavones, and flavonols and a direct extraction method for the flavan-3-ols and flavanones. Experimental results compare favorably (few statistically significant differences) to literature values in the flavonoid and proanthocyanidin database previously compiled by the Nutrient Data Laboratory. The results of this study showed a seasonal variation only for blueberries. This study also showed that the variation in the flavonoid content of foods, as purchased by the U.S. consumer, was very large. The relative standard deviation, averaged for each flavonoid in each food, was 168%.