Tannins of Grain Sorghum: Luteoforol (Leucoluteolinidin), 3′,4,4′,5,7‐Pentahydroxyflavan

Abstract

SUMMARY– The principal tannin of sorghum is a leuco‐anthocyanin yielding luteolinidin (3′,4′,5,7‐tetrahydroxy‐flavylium) when heated with mineral acid. The precursor, luteoforol, has most of the properties of 3′,4,4′,5,7‐penta‐hydroxyflavan prepared by reduction of eriodictyol. Luteoforol, when treated with concentrated mineral acid in the cold, gives a purple color with Λ max 550nm. A method for the determination of luteoforol in sorghum, based on this property, is described. The results with a number of varieties of sorghum are compared with those obtained by the AOAC Folin‐Denis method. The contribution of luteoforol to the “tannin” so determined varies from 1 to < 25%. Except for one sample of Kaffir corn, which contained leucocyanidin as well as luteoforol, no other tannins were detected. The “tannin” content varied widely, (from 0.05 to 0.67% as tannic acid), a white‐skinned variety having the least. The uniformity of commercial samples can be rapidly evaluated by single‐grain determinations of luteoforol.