Immature corn as a source of niacin for rats.

The variability in the concentration and biological availability of niacin in corn was investigated. Plots of both sweet and field corn were harvested at different stages. In rat growth assays for available niacin, grains harvested at the immature, "milky" stage and then dried gave values of 88 and 74 micrograms/g, respectively. These values were in contrast to the low growth assay values of 18 and 16 micrograms/g for grain harvested at maturity, and even higher than the value of approximately 56 micrograms/g obtained for each immature corn in both the Association of Official Analytical Chemists procedure of chemical analysis and a standard microbiological procedure. However, when the milky grains were precooked at neutral pH, the values from these procedures were higher and agreed with the biological assay results. It is suggested that, during the initial alkaline digestion used for these two procedures, a proportion of the niacin in NAD, the major form of niacin in milky corn, degrades. However, when the materials are first cooked at neutral pH, nicotinamide is released without loss, and the pyridine ring is then stable. The traditional American Indian practice of roasting and drying "green corn" apparently provided a valuable source of niacin.