The conversion of procyanidins and prodelphinidins to cyanidin and delphinidin

The hydrolysis of proanthocyanidins to anthocyanidins in n-BuOH-HCl (95:5) has been shown to be an autoxidation, the yield of anthocyanidin being critically dependent on trace metal-ion impurities. Reproducible yields of anthocyanidin may be achieved if iron (III) salts are added to the reaction medium, and a standard method of analysis of proanthocyanidins based on use of an n-BuOH-HCl-Fe^III mixture is given. The ratio of absorbance maxima of the cyanidin (550 nm) produced to that near 280 nm for the original procyanidin polymer solution was ～ 3.5.