Determination of thiol groups and disulphide bonds in wheat flour and dough

A study was made of the conditions for determining all thiol (SH) groups and disulphide (S—S) bonds in wheat flour and dough. Thiol groups were determined by amperometric titration with Ag2SO4, the flour or dough which contains proteins and peptides being suspended in a solution of 6 m urea and 10−4 M sodium dodecyl sulphate (SDS). The potential of the platinum electrode was −0.24 V vs calomel reference electrode. Disulphide bonds were determined in two ways: (a) Using an excess of Ag2SO4 in the presence of 9 M urea; when the reaction was finished, the excess Ag2SO4 was removed by adding an exact quantity of glutathione. The glutathione which remained after binding the Ag2SO4 excess was determined by amperometric titration with a 5.10−5 M Ag2SO4 solution, (b) Determination after reduction with NaBH4; the disulphide bonds were reduced to thiol groups and the total amount of thiol groups was determined with Ag2SO4. The results indicated that wheat flour contains 5–7 μmol SH‐groups, which is about six times the level found by previous workers, and 11‐18 μmol disulphide bonds per gram flour. A correlation with baking quality was not observed.