Oxidation of polyphenols in phytate-reduced high-tannin cereals: effect on different phenolic groups and on in vitro accessible iron.

After reduction of phytate with phytase, water slurries of two high-tannin cereal flours were incubated with polyphenol oxidase (mushroom tyrosinase), and the effects on different phenolic groups and on in vitro accessible iron were studied. Enzyme incubation was also performed after cooking, soaking, and germination of the cereals. Phytase incubation significantly decreased the phytate content, and incubation with polyphenol oxidase had a reducing effect on the total phenol content, as well as on the amount of catechol and resorcinol groups. The in vitro accessible iron increased when the cereals were incubated with phytase and polyphenol oxidase, and the highest accessibility of iron was obtained when the germinated samples were incubated. The results from this study imply that oxidation of polyphenols in high-tannin cereals, after reduction of phytate, may be used to increase the bioavailability of iron in foods prepared from these cereals.