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

Abstract

Abstract 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 Ag 2 SO 4 , 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 Ag 2 SO 4 in the presence of 9 M urea; when the reaction was finished, the excess Ag 2 SO 4 was removed by adding an exact quantity of glutathione. The glutathione which remained after binding the Ag 2 SO 4 excess was determined by amperometric titration with a 5.10 −5 M Ag 2 SO 4 solution, (b) Determination after reduction with NaBH 4 ; the disulphide bonds were reduced to thiol groups and the total amount of thiol groups was determined with Ag 2 SO 4 . 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.