Isolation and characterisation of wheat flour proteins. IV.—effects on wheat flour proteins of dough mixing and of oxidising agents†

Proteins dispersible in 3M-urea increased from about 65 to 85% during mixing of dough in Farinograph. The increase was positively correlated with length of mixing. Protein dispersibility was highest in doughs mixed with five-fold excess potassium iodate, and was lowest in flours. Intermediate amounts of proteins were extracted from doughs mixed in air, in a nitrogen atmosphere, or in air with a five-fold excess of potassium bromate. Proteins, extracted with 3M-urea from doughs mixed to optimum consistency, were separated by fractionation on Sephadex G-100 columns into at least 6 fractions, constituting 3 distinct peaks. Distribution of proteins in the peaks was measured by Kjeldahl-N, biuret, and absorbance at 280 mμ methods. Mixing in air, but not in a nitrogen atmosphere, increased substantially the amount of proteins with a molecular weight above 150,000 and decreased the amount of low molecular-weight proteins. The effects of mixing bromated doughs were similar to mixing plain doughs in air, but the chemical modifications in bromated doughs were much more pronounced. No such changes were observed in iodate-treated doughs. Similar changes in distribution of protein fractions were observed when the gross protein extracts or Sephadex-fractionated proteins were studied by electrophoresis on starch gel in the presence of 3M-urea.