Effects of reactive oxygen and temperature on the formation of a purple pigment, hordeumin, from barley bran-fermented broth

A purple pigment called hordeumin, a type of anthocyanin-tannin pigment, is produced from barley barn-fermented broth. Hordeumin is a precipitate formed by storing fermented filtrate containing hordeumin precursors in an oxidative environment. Hordeumin formation was inhibited by addition of radical scavengers or antioxidants to the barley bran-fermented filtrate. The addition of iron ion accelerated hordeumin formation, and the addition of DETAPAC, an iron ion chelating reagent, influenced the color tone of hordeumin. These findings suggest that hordeumin formation may be an oxygen-mediated reaction, involving reactive oxygen species. Furthermore, hordeumin formation was accelerated by increasing the hordeumin formation temperature (from 5 to 60 degrees C). The color quality of the hordeumin that was produced at high temperature was almost the same as that hordeumin produced at 5 degrees C.