Cereal Chem 38:272 - 280.  |  VIEW ARTICLE

The Oxidation of Wheat Flour. I. Measurement of Sulfhydryl Groups.

B. Sullivan, L. Dahle, and E. Larson. Copyright 1961 by the American Association of Cereal Chemists, Inc. 

Although p-chloromercuribenzoate (PCMB) reacts specifically with free sulfhydryl groups, these groups can still be measured in the presence of PCMB by amperometric titration with mercuric chloride. Mercuric chloride apparently displaces the PCMB from -SH groups, the mercuric chloride possessing a stronger affinity for the -SH groups than PCMB. This provides a useful technique for protecting -SH groups during measurement and results in higher values. The -SH content of flour is about equally divided between the water-soluble and the gluten proteins. No -SH has been found in the lipid or starch fraction of flour. The lipids of germ do contain sulfhydryl groups.