| Sumario: | Differences in the distribution of physical fractions and of nitrogen in maize samples of normal genetic composition, as well as in Opaque-2 and Floury-2 maize are reported. The results indicate that Opaque-2 maize contains a larger germ than a normal maize, and that it contributes greater amounts of nitrogen. This, together with a greater content of lysine and tryptophan in the endosperm of Opaque-2 maize than in the normal grain, may explain the significantly higher-quality value of the protein of Opaque-2 in comparison with that of the normal samples. Floury-2 maize also has a large-germ, wich is propably the responsible factor of the higher protein content of the kernel, although not as significant as that found in Opaque-2 maize.
A fast chemical methodology useful to detect differences between normal and Opaque-2 maize requiring only small amounts of samples is also presented. The study reavealed that a nitrogen fraction, at present called "non protein nitrogen fraction" and free lysine are contained in significantly greater amounts in Opaque-2 than in normal maize.
Biological tests carried out in rats confirmed the greater PER values of Opaque-2 maize in comparison with those of normal and Floury-2 samples. Likewise, those animals fed maize, had slightly lower blood urea levels when Opaque-2 was administered than when normal or Floury-2 maize were used as rations. However, at present this method is not sufficiently sensitive to use as a screening tool for the selection of varieties of improved nutritive value.
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