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The Available Niacin Values of Foods for Rats and Their Relation to Analytical Values¹

Department of Nutritional Sciences, University of California, Berkeley, CA 94720

A bioassay for niacin was developed using weight gain or "gain/food eaten" of young rats as the response measure. The best basal diet contained casein 70 and gelatin 65.5 g/kg together with supplementary tryptophan to a total of 0.97 g/kg and other amino acids to meet requirements. After a 4-day depletion period, rats gained ca. 1 g/day over the next 20 days on the basal diet alone, or ca. 7 g/day with 12 mg/kg added nicotinic acid. Test foods were added at two levels with diets adjusted to keep constant amino acid composition. The results were compared with chemical analyses for total niacin (i.e., in extracts prepared from samples digested with alkali) and for free niacin (using extracts made at neutral pH) with separation of nicotinic acid and nicotinamide on thin-layer chromatograms or Sephadex columns. Eight samples of mature cooked cereals, with their niacin largely in bound forms, gave rat assay values equivalent to ca. 35% of their total niacin content. Alkali-cooked tortillas, steamed sweet corn, beans and liver, with their niacin all in free form, gave assay values close to their total niacin content. Baked potatoes and peanut flour were intermediate in both respects.

KEY WORDS: • niacin • rats • bioassay • cereals • bound niacin • bioavailability

¹ Parts of the data are from a dissertation submitted by Eric G. A. Carter in partial fulfillment of requirements for the Ph.D. degree in the University of Cambridge. A preliminary report was presented to the American Institute of Nutrition, April 15, 1980 Fed. Proc. 39, 557 (1980). The work was begun at the Department of Applied Biology, University of Cambridge, England, with a grant from the Medical Research Council and completed in California with a grant (no. 22492) from the U.S. Department of Agriculture.

Manuscript received 29 March 1982.