DEVELOPMENT OF ACCURATE AND REPRESENTATIVE FOOD COMPOSITION DATA FOR THE U.S. FOOD SUPPLY
Location: Nutrient Data
Title: Stability of vitamin C in frozen raw fruit and vegetable homogenates
Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 26, 2009
Publication Date: May 15, 2009
Citation: Phillips, K.M., Tarragó-Trani, M.T., Gebhardt, S.E., Exler, J., Patterson, K.Y., Haytowitz, D.B., Pehrsson, P.R., Holden, J.M. 2010. Stability of vitamin C in frozen raw fruit and vegetable homogenates. Journal of Food Composition and Analysis. 23(3):253-259.
Interpretive Summary: The nutritional importance of vitamin C as an essential water-soluble vitamin is well established, and an adequate intake of vitamin C from foods and/or supplements is vital for normal functioning of the human body. Information on the vitamin C content of foods is available from U.S. Department of Agriculture's (USDA) National Nutrient Database for Standard Reference (SR). The USDA National Food and Nutrient Analysis Program (NFNAP)is an ongoing project to update and improve the quality of food composition data in SR. As a part of that program, raw fruits and vegetables are analyzed for vitamin C. It is important that the data collected be accurate so it is necessary to be sure that the vitamin C in the samples does not change before analysis.
In the NFNAP program, primary samples units are generally collected from supermarkets around the country and shipped to a central location for processing prior to analysis for many nutrients by various laboratories. This study was designed to determine if vitamin C is retained in the samples with the usual processing procedures, and how long it is retained in the frozen samples during storage.
Three kinds of fresh produce were tested: raw collard greens, russet potatoes, and clementines. The samples were homogenized in liquid nitrogen, put into glass jars, stored at -60 degrees C, and protected from light. Analyses of the materials for vitamin C were done immediately and on the stored samples after 2 weeks, 1, 2, 3, 4, 6, and 12 months using an accurate, validated analytical method. No significant change in the vitamin C content of clementines was noted over a year, but, for both the potatoes and collard greens, a steady decrease in content was seen after one month of storage.
It was determined that the tested food samples processed using the usual NFNAP procedures, and analyzed for vitamin C within a month, give reasonably accurate results. Longer term storage prior to analysis, for some types of foods, would result in a loss of vitamin C and give inaccurate results.
Retention of vitamin C in homogenized raw fruits and vegetables stored under laboratory conditions prior to analysis was investigated. Raw collard greens, clementines, and potatoes were chosen, to be representative of food matrices to be sampled in USDA’s National Food and Nutrient Analysis Program (NFNAP), and having different expected stability of ascorbic acid (AA). Samples were homogenized in liquid nitrogen, assayed immediately, then stored at -60 degrees C and analyzed at eight time points up to 49 weeks. Vitamin C (as total AA after reduction of dehydroascorbic acid), was analyzed using a validated method with quantitation by HPLC/ultraviolet detection. An orange juice control sample was included in each run.
Vitamin C content was stable in clementines and the orange juice control samples, but decreased in collards and potatoes [16.8 and 10.9 mg/100g (14.7% and 30.4%), respectively, after 49 weeks]. Significant losses had occurred after 12 weeks. These results suggest that careful attention to sample handling protocols is required for raw products with similar matrices, or AA values may not reflect the concentration in the food as consumed. The control sample was critical to allowing assessment of storage effects independent of analytical variability. Fruits and vegetables for the NFNAP will be analyzed without storage until a practical stabilization protocol is validated.