Development of a database of critically evaluated flavonoids data: application of USDA's data quality evaluation system

The USDA Special Interest Database for flavonoid content of selected foods contains 26 most abundant compounds within 5 predominant subclasses of flavonoids-flavonols, flavones, flavanones, flavan-3-ols, and anthocyanidins. All the data were evaluated for 5 quality evaluation categories (sampling plan, sample handling, analytical method, analytical quality control and number of samples), using the data quality evaluation system developed by the USDA scientists. Confidence Codes (A-through D) were then assigned to every value. The database contains acceptable values for 225 selected foods. Only 97 sources out of approximately 475 collected included acceptable analytical data. The overall quality of data was good with 64% of the observations receiving A or B confidence codes; the flavan-3-ols subclass received better ratings than other subclasses. While this is the first comprehensive database for flavonoids in foods, the majority of data came from Europe and countries other than the US. Due to the observed variability in the values it will be important to have data for US foods. The evaluation of data quality helps set priorities and further identifies the foods to be analyzed as well as areas to improve data quality. Furthermore, release of data quality confidence codes with data provides necessary information to investigators to assess the impact of flavonoid intake on risk of various chronic diseases.