Phenols of sorghum and maize : the effect of genotype and alkali processing

Abstract

The color and phenols of sorghum were controlled by the R, Y, B(,1), B(,2), and S genes. Relatively pure fractions of pericarp, testa and endosperm were isolated by abrasive milling. Phenols and tannins were concentrated in the pericarp and testa, with only bound phenols present in the endosperm. Ferulic acid was the major bound phenol and was associated with the cell walls. Group I and II sorghums with a red pericarp (RRYY) contained more anthocyanidin pigments than those with a white pericarp (RRyy), but the pigments of Group III were not affected by pericarp color. Dominant B(,1) and B(,2) controlled the presence of tannins and increased the levels of total phenols, but decreased the level of phenolic acids in the pericarp and testa. When the pigmented testa was present dominant S increased the levels of tannins and phenols in the pericarp and testa. The chain length of the tannins was not affected, but the solubility was altered when S was dominant. Maize and Group I sorghums had similar levels of Folin-Ciocalteu (FC) phenols. Phenolic acids accounted for 30-40% of the FC phenols of maize, but only 6% for Group I sorghums. Sorghum contained a greater variety of phenolic acids. Grain and cob color of maize did not effect the level of FC phenols. Grain color did not effect the phenolic acids of maize but red cob maize varieties had higher levels of phenolic acids. A pH of approximately 8 was required for off-color formation in sorghum tortillas. An alkali level of 0.8% was required to reach this tortilla pH. Phenols were bound during cooking and were responsible for a portion of the off-colors. Maize varieties with red cobs also produced off-colored tortillas. Color formation in maize appeared to be a different mechanism, with phenolic compounds of less importance. The color of sorghum tortillas was improved by adding reducing, chelating and bleaching agents to the cooking or wash water. At levels high enough to improve the color (1000 ppm), odor and flavor of the tortilla were adversely affected. Pearling, reduction of alkali, or a combination would be practical methods to improve the color of sorghum tortillas.