USE OF A MICROBIOLOGICAL ASSAY WITH TRI-ENZYME EXTRACTION FOR MEASUREMENT OF PRE-FORTIFICATION LEVELS OF FOLATES IN ENRICHED CEREAL-GRAIN PRODUCTS

January 1, 1998 was the effective date for FDA regulations that mandat ed the fortification in the USA of a wide range of enriched cereal-gra in products with folic acid at levels specified in federal regulations . Because data on prefortification levels of folate in such products a re limited, we measured folate in 56 enriched foods, including enriche d breads and rolls, flours, corn grits and meals, rices, and macaroni and noodle products. Folate was measured by a modification of the Asso ciation of Official Analytical Chemists' microbiological method 992.05 using Lactobacillus casei. Foods were composited, suspended in 0.1 M phosphate buffer containing 1% ascorbic acid (pH 7.8), autoclaved and cooled. Chicken pancreas conjugase was added and the suspensions were incubated for 16 h at 37 degrees C. Values for folate in enriched prod ucts were (mu g/100 g): bread and rolls, 24-40; flours, 19-24; corn gr its and meals, 22-32; macaroni and noodle products, 27-42; rice, 19-32 . Because the single-enzyme method is usually insufficient to liberate food-bound folates, suspensions of foods were also incubated with alp ha-amylase and conjugase followed by treatment with protease to determ ine the effects of the tri-enzyme digestion on release of folates. For many foods, total folate was 20-30% higher after the tri-enzyme diges tion than after incubation with conjugase alone. The modifications of AOAC method 992.05 described here provide a microbiological assay meth od for the determination of folates in cereal-grain products that may be appropriate for collaborative testing. (C) 1998 Elsevier Science Lt d. All rights reserved