Isolation of Proteins from Plant Material

SUMMARY Proteins were extracted with a yield of up to 90% from wheat flour and finely powdered untoasted soya flour, with a 3M urea solution at 4°C. The urea‐extracted protein contained, on hydrolysis, higher amounts of ammonia than a commercial soya protein isolate. Amino acid analysis by ion‐exchange chromatography of soya proteins isolated with 3M urea showed that, on an ammonia‐free basis, the urea‐extracted proteins were comparable to a commercial soya protein isolate. Both had an amino acid composition comparable to that of a commercial solvent‐extracted 50y0‐protein soya meal. The urea‐extracted proteins from wheat flour and soya flour retained their functional properties in bread‐making. Extraction with 3M urea was lowered in coarsely ground soya meals and was reduced substantially by heat‐treatment of soya products. Dispersibility in 3M urea at 4°C was found to be a useful parameter to evaluate the extent of heat damage to plant proteins.