Cereal Chem 49:104 - 118.  |  VIEW ARTICLE
The Relation Between the Thiol and Disulfide Contents of Dough and its Rheological Properties.

A. H. Bloksma. Copyright 1972 by the American Association of Cereal Chemists, Inc. 

In doughs mixed in nitrogen and with various additions of the oxidizing reagents potassium bromate or iodate, of the thiol-blocking compound N-ethyl maleimide, or of the thiol compound glutathione, or mixed in air or oxygen, thiol (-SH) and disulfide groups (-SS-) were titrated with silver nitrate. Total contents of these groups were determined in the presence of 4 and 9M urea, respectively; titrations in the absence of urea produced the contents of the reactive SH and SS groups. From creep and recovery tests at a range of shear stresses the compliance was derived, which could be divided into a viscous (permanent) and an elastic (temporary) part. In addition, extensigrams were recorded. The results show that there is no unequivocal relation between the total SH content and various rheological properties. If all oxidizing or thiol-blocking reagents are added in amounts so as to produce the same decrease in thiol content, the rheological effect of bromate is much larger than that of iodate or N-ethyl maleimide. The behavior of oxygen is intermediate between those of bromate and iodate. A small increase in thiol content owing to glutathione has about the same effect, though in opposite direction, as an equal decrease in thiol content caused by iodate or N-ethyl maleimide. In the range of additions in which rheological measurements could be performed, the ratio of reactive to total SH groups varied little; as a consequence, the above conclusions are also valid for the reactive SH content. No correlations between the total, reactive, or nonreactive SS content and the elastic properties of dough were found. For the explanation of earlier results, it was supposed that the rheologically effective SH and SS groups are only fractions of the total contents of these groups. The present results suggest that the rheologically effective fractions are even much smaller than the chemically reactive ones. If this explanation is true, the slowly acting promate reacts more specifically with the rheologically effective fractions than do the rapidly acting iodate and N-ethyl maleimide.