Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/4/2004
Publication Date: 4/1/2005
Citation: Phillips, K., Wunderlich, K., Holden, J.M., Exler, J., Gebhardt, S.E., Haytowitz, D.B., Beecher, G.R., Doherty, R.F. 2005. Stability of 5-methyltetrahydrofolate in frozen fresh fruits and vegetables. Journal of Agricultural and Food Chemistry. 97:587-595. Interpretive Summary: A large variability in folate values is often found for food samples. This study was undertaken to determine the variability in folate values due to sample handling during the measurement process. Six fresh fruits and vegetables from the National Food and Nutrient Analysis Program (NFNAP), representing a range of food matrices and folate concentrations, were selected for study. Edible portions from the foods were homogenized and stored at -60oC until ready for analysis of 5-methyltetrahydrofolate (5MTHF). Control materials used were a commercial reference material with an indicative value for 5MTHF and a canned spinach composite. The produce samples were analyzed for 5MTHF after 0, 1, 2, 7, 30 days and at 3-month intervals. The results of the study indicate that fresh fruits and vegetables may be homogenized and stored frozen under the conditions typical of NFNAP samples for up to 12 months with no loss of 5MTHF beyond the limits of analytical variability.
Technical Abstract: The stability of 5-methyltetrahydrofolate (5MTHF) in homogenized fresh fruits and vegetables representing samples for the U.S. Department of Agriculture's (USDA) National Food and Nutrient Analysis Program (NFNAP) was evaluated. Samples were homogenized in liquid nitrogen, and 5MTHF was measured after 0, 1, 2, 7, 30 days and then at 3-month intervals for a total of 12 months storage at -60±5oC, utilizing extraction by a tri-enzyme treatment, purification by anion-exchange solid-phase extraction, and quantification by reverse-phase HPLC. Method validation included analysis of a reference material and inter-laboratory analysis of selected samples by HPLC and LC-MS. A canned spinach composite was assayed in each analytical batch to monitor inter-assay precision. No change in 5MTHF content was detected in any of the samples after 12 months. Concentrations ranged from <10ug/100g in bananas to >100ug/100g in spinach. Relative standard deviations were generally <7% within assay and <11% between assays.