Sorghum tannin and non-tannin phenols: Absorption and toxicity in chicks and rats, and their chemical characterization

The absorption and distribution of sorghum tannin and non-tannin phenols were evaluated by orally administering to chicks ;No phenols were detected in the plasma of chicks fed non-radiolabeled tannin or non-tannin phenolic fractions (prepared in large scale, 2% of the diet, in weight). However, when rats were fed similar diets, an increased phenolic content was noted in the plasma of those fed the purified tannin and ethyl acetate fraction. These data indicate that phenols were absorbed from the digestive tract of rats. For the purified tannin, the absorption of dimeric proanthocyanidins and/or low molecular weight phenols resulting from contamination by other fractions during the large scale fractionation, is suggested.;The purified tannin was the most toxic fraction reducing feed consumption and growth rate in chicks and rats. In addition, the purified tannin caused a reduction in the apparent digestible energy (rats), the digestibility of nitrogen (chicks and rats) and amino acids (rats), and nitrogen retention (rats), as compared to the low tannin diet. Poorer performance was also seen in rats fed the water-insoluble and ethyl acetate fraction diets. This suggests that both polymeric polyphenols and low molecular weight phenols from the former and latter, respectively, may be also associated with the adverse effects seen in rats fed diets with whole high tannin sorghum grains. Finally, chicks fed the purified tannin did not show any leg anomalies, but those on the ethanol fraction diet had as many leg disorders as the high tannin control. It is suggested that the toxic factors related to leg anomalies in chicks may be contained in the ethanol fraction.;Chemical characterization studies showed that the phenolic fractions of high tannin sorghum were different from each other, with the non-tannin fractions composed mostly of low molecular weight phenols. In contrast, tannin and the water-insoluble fraction were apparently composed of a group of similar proanthocyanidins, with the latter having higher molecular weight than the former. The purified tannin, water- insoluble and ethyl acetate fractions showed an ability to precipitate protein, suggesting a potential nutritional significance, which was confirmed in the rat experiment.