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Folic acid in enriched cereal-grain products by immunoassay. J. I. RADER. Center for Food Safety and
Applied Nutrition, Food, and Drug Administration, Washington, DC 20204.
The ability to quantitate folic acid in foods is important because FDA
regulations mandate the addition of this form of the vitamin and because the Institute of Medicine (IOM)
recently set the new Recommended Dietary Allowance (RDA) for folate for adults in terms of dietary folate
equivalents (DFE). The DFE adjusts for the lower availability of natural folate compared with that of
synthetic folic acid. A recent collaborative study has determined the utility of the microbiological assay with
trienzyme digestion for the measurement of total folate. This assay does not measure free folic acid. We
investigated an immunoassay kit (RIDASCREEN FAST Folic Acid, r-Biopharm, GmbH, Darmstadt,
Germany and Marshall, MI) for measuring folic acid in enriched cereal-grain products. Fortified foods and
AACC check samples were suspended in water and solubilized by autoclaving. Extracts were filtered,
diluted, and added to antibody-coated wells on the test's microtiter plates. Tests were performed according
to kit directions. Products were also analyzed by microbiological assay with trienzyme treatment. Values
determined by immunoassay were 43-110% of those obtained by microbiological assay. Agreement
between the two methods was greater for products expected to contain high amounts of folic acid as a
fortificant than for those of lower folate content.
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