Sorghum kafirin interaction with various phenolic compounds

The ability of various phenolic compounds to bind and precipitate kafirin, the prolamin protein of sorghum, was investigated with regard to effects on its nutritional and functional uses. The protein-phenolic compound interaction was quantified by haze formation and colorimetric determination of total polyphenol bound. Ferulic acid, catechin and extracted phenolics (flavonoids) from condensed tannin-free sorghum did not complex kafirin. Only tannic acid and sorghum-condensed tannins had the ability to complex kafirin. The sorghum-condensed tannins interacted more strongly than tannic acid. The haze of sorghum-condensed tannins-kafirin was permanent, indicating a strong interaction. The fact that sorghum-condensed tannins can bind irreversibly to kafirin indicates that this may play a role in decreasing protein digestibility in high-tannin sorghum and can cause haze formation in lager beer made from high-tannin sorghum. However, in condensed tannin-free sorghum, phenolic compounds may not appear to play a major role in decreasing protein digestibility, as these endogenous phenolics may not bind with kafirin. (C) 2003 Society of Chemical Industry.