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Early attempts to estimate human niacin requirement were based on calculations of the niacin content of pellagragenic and nonpellagragenic diets (1, 2). It was appreciated that the protein content of the diet was in some way related to niacin requirement. Recent studies showing that the amino acid tryptophan is converted in part to niacin compounds in man (3-5) may explain the above relationship, and also the pellagra preventive effect of foods which are low in niacin but rich in "good" protein.The present experiments were designed to study niacin requirement in man with diets of known tryptophan content. Estimation of minimum tryptophan requirement for nitrogen balance (6) permits formulation of diets containing little excess tryptophan which may be converted to niacin. The discovery of the major metabolites of niacin, namely Nl-methylnicotinamide (N'-Me) and the 6-pyridone of Nl-methylnicotinamide (pyridone), and the development of methods for the measurement of these compounds in urine, now permit more complete studies of niacin metabolism (7-11).Seven subjects were maintained on diets low in niacin and tryptophan for from 40 to 135 days and the urinary excretion of niacin metabolites was determined. Clinical signs of pellagra developed in the three subjects who remained on one of these diets for more than 50 days. METHODSThe seven subjects were white females, 25 to 54 years of age, who were found to be essentially free of organic ',This work was supported by grants from the Nutri- The diet for two complete days was analyzed at intervals for niacin, tryptophan and total nitrogen. The diet for each meal was blended with water in a Waring blendor to give a total volume of 1,000 to 1,500 ml. Aliquots of this material were autoclaved in 1 N sulfuric acid solution for 45 minutes, neutralized and analyzed for niacin microbiologically, using L. arabinosus (12). This organism was also employed for tryptophan analysis using aliquots of the homogenate which had been autoclaved in 5 N sodium hydroxide in the presence of cysteine (13). For these analyses 15 ml. portions of 8 N sodium hydroxide solution were placed in 125 ml. Erlenmeyer flasks and 400 mg. of cysteine and 10 ml. of the blended diet were rapidly added. These were covered at once with beakers and autoclaved for six hours at 1210 C.After neutralization with hydrochloric acid, the solutions were diluted to 100 ml., filtered and analyzed. Under these conditions it is assumed that all tryptophan. liberated from the proteins was racemized and was present as D,L-tryptophan. Although it is possible that some tryptophan in the proteins may have been destroyed by this procedure, L-or D,L-tryptophan added to the samples was not destroyed and treatment of L-or D,L-tryptophan alone with these reagents resulted in 90 to 100% recovery. Analyses of the diets and of individual foods gave reproducible results. Nitrogen was determined by the macro-Kjeldahl method.All urine was collected for 24 hour periods in dark bottles containing 5 ml. of glacial acetic acid and kept in th...

Pilot plant batches of liquid soy isolate infant formula products were prepared without added iron and with various added iron salts by standard commercial techniques. Three of the iron salts also were added without processing to lyophilized product made without added iron. Measured amounts of the lyophilized products were fed to anemic rats; hemoglobin responses were used to evaluate iron availability. Processing had little effect on the availability of ferrous sulfate, whereas it increased the relative availability of the iron of ferric pyrophosphate from 39 to 93, expressed as a percentage of reagent grade ferrous sulfate, and of sodium iron pyrophosphate from 15 to 66. The iron in a production batch of a commercially available soy isolate infant formula containing sodium iron pyrophosphate as the added iron salt had a relative availability of 77. The results indicate that the availability of iron added to foods should be determined only after normal processing.

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