Bound Nicotinic Acid in Dietary Wheaten Products.

In cereals, nicotinic acid occurs mainly in a bound form, niacytin, which is nutritionally unavailable to certain bacteria and mammals (Kodicek & Wilson, 1960). Most published findings relating to nutritional availability have been on rats and pigs, and the results have been in agreement with microbiological assays (Braude, Kon, Mitchell & Kodicek, 1955 ; Kodicek, Braude, Kon & Mitchell, 1956, 1959; Kodicek & Wilson, 1959; Kodicek, 1960; Carpenter, Kodicek & Wilson, 1960; Chaudhuri & Kodicek, 1960). It is known that the nicotinic acid metabolism of pigs is similar to that of man, although there is no direct evidence about the availability of the bound form to man. In Britain, 20-30% of the total dietary nicotinic acid intake comes from cereals, and it therefore seemed of interest to establish the nutritional availability of the vitamin from this source. It is known that bound nicotinic acid is liberated by treatment of the cereal with dilute alkali. My investigation was undertaken to find the percentage of free nicotinic acid, determined by microbiological assays, in wheat constituents of the human diet. The survey was made on brown breads, wheaten scones, ' digestive' biscuits and wheaten breakfast cereals. These products all contain a high proportion of the bran and aleurone fractions, which in turn contain about 85 yo of the nicotinic acid of the wheat grain. White-flour products are of less interest, since compulsory fortification results in so high a free nicotinic acid level that the bound form of the vitamin can be of little nutritional significance.