Seasonal variability of the vitamin C content of fresh fruits and vegetables in a local retail market.

Background: Seasonal variation of vitamin C in fresh fruits and vegetables is not reflected in food composition database average values, yet many factors influence content and retention.

Results: Fresh fruits and vegetables were sampled on three occasions in each season, from the same local retail outlets, for 1 or 2 years. Vitamin C was significantly higher in winter-sampled spinach (436 mg kg ) compared with spring (298 mg kg ) and summer/fall (180 mg kg ); in potatoes in summer/fall (156 mg kg ) versus winter/spring (106 mg kg ); and in oranges in winter (616 mg kg ), spring (592 mg kg ), and summer (506 mg kg ).

Quality-control materials in the USDA National Food and Nutrient Analysis Program (NFNAP).

The US Department of Agriculture (USDA) Nutrient Data Laboratory (NDL) develops and maintains the USDA National Nutrient Databank System (NDBS). Data are released from the NDBS for scientific and public use through the USDA National Nutrient Database for Standard Reference (SR) ( http://www.ars.