Contents of tannins of cultivars of sorghum cultivated in Brazil, as determined by four quantification methods

High tannin content in sorghum grains is an undesirable characteristic for poultry and pig feeding and represents a challenge for breeding programs. On the other hand, moderate content of tannins in sorghum may be beneficial in human diets because they exert anti-cancer, anti-inflammatory and reduced carbohydrate uptake effects, among others. The aim of this study was to compare tannin contents of twenty sorghum cultivars available in Brazil, as well as to compare results obtained with four methods of tannin quantification: butanol/HCl, vanillin/HCl, BSA/FeCl₃ and PVPP/Folin-Ciocalteu. The results obtained with butanol/HCl and vanillin/HCl were higher than with BSA/FeCl₃ and PVPP/Folin-Ciocalteu. A known amount of purified quebracho tannin was used to test the validation of methods of tannin quantification and vanillin/HCl stood out for its high accuracy degree. The sampling used reveals wide genetic diversity regarding tannin contents. The expectation of predicting tannin contents on basis of grain color seems unfeasible.

Keywords: Butanol/HCl; PVPP/folin-ciocalteu; Quebracho tannin; Sorghum bicolor; Vanillin/HCl.