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United States Department of Agriculture

Agricultural Research Service

Title: Comparison of Total Folate Concentration in Foods Determined by Microbiological Assay at Several Experienced Laboratories

Authors
item Koontz, J - VPI
item Phillips, K - VPI
item Wunderlich, K - VPI
item Exler, Jacob
item Holden, Joanne
item Gebhardt, Susan
item Haytowitz, David

Submitted to: Journal of Association of Official Analytical Chemists International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 2, 2004
Publication Date: June 1, 2005
Citation: Koontz, J., Phillips, K., Wunderlich, K., Exler, J., Holden, J.M., Gebhardt, S.E., Haytowitz, D.B. 2005. Comparison of total folate concentration in foods determined by microbiological assay at several experienced laboratories. Journal of Association of Official Analytical Chemists International. 88(3):805-813.

Interpretive Summary: Most folate analyses for nutrient databases and nutrition labeling are performed by fee-for-service laboratories. In order to select the best lab for performing folate analysis for the National Food and Nutrient Program (NFNAP), it is necessary to know how well a laboratory will perform on the analysis of reference materials and different matrix food samples. Six different types of food samples were sent to four experienced laboratories that regularly perform folate analysis on fee-for-service basis. An aliquot of each food composite and of three certified reference materials were sent on each of four occasions to the four laboratories. Results for macaroni and pizza, the only folic acid-fortified foods, had considerably lower between-laboratory variation (CVB) with CVB of 9-11% versus >45% for other foods. Only one laboratory reported using a tri-enzyme extraction, currently recognized as the preferred extraction procedure, and all laboratories used folic acid fortified foods as internal control materials. Users of commercial total folate analysis should understand the uncertainty in values determined by microbiological assay, particularly for foods containing primarily naturally occurring folate. Caution should be used in selecting laboratories to perform folate analyses.

Technical Abstract: Analysis of total folate concentration measured by microbiological assay in a variety of foods submitted in a routine manner to experienced laboratories that regularly perform folate analysis on fee-for-service basis was evaluated. Homogenates of fresh strawberries, frozen spinach, orange juice, frozen meat and vegetable pizza, dry macaroni, and dried pinto beans were prepared and stored under conditions previously determined to maintain stability of folate content. An aliquot of each composite and of three certified reference materials were sent on each of four occasions to four laboratories. Results for macaroni and pizza, the only folic acid-fortified foods, had considerably lower between-laboratory variation (CVB) with CVB of 9-11% versus >45% for other foods. Mean total folate ranged from 14 to 279 ug/100g for a mixed vegetable reference material, from 5 to 70 ug/100g for strawberries, and from 28 to 81 ug/100g for whole meal flour. Only one laboratory reported using a tri-enzyme extraction, and all laboratories used folic acid fortified foods as internal control materials. Users of commercial total folate analysis should understand the uncertainty in values determined by microbiological assay, particularly for foods containing primarily naturally occurring folate, which may not be apparent when replicate samples are not submitted for analysis.

Last Modified: 7/30/2014