Cereal Chem 57:159 - 163.  |  VIEW ARTICLE
Mixograph Studies. III. Reaction of Fumaric Acid with Gluten Proteins During Dough Mixing.

J. S. Sidhu, P. Nordin, and R. C. Hoseney. Copyright 1980 by the American Association of Cereal Chemists, Inc. 

The effect of fumaric acid on the mixograph curve is similar to that of N-ethylmaleimide. After the peak, extensive dough breakdown results in a narrow mixogram tail. In this study, about 2% of 50 microCi of 14C-fumaric acid was incorporated into gluten proteins during 9 min of dough mixing. Most of the added fumaric acid was found in the water-soluble fraction as free fumaric acid. Gel filtration on Sephadex G-200 showed that most of the bound 14C-fumaric acid was associated with the higher molecular weight protein fraction. Although most of the free sulfhydryl groups in flour are found in the water-soluble fraction, only a small amount of the 14C-fumaric acid reacted with water-soluble proteins. Hydrolysis of gluten proteins containing bound 14C-fumaric acid, using pronase or 3 N p-toluenesulfonic acid, gave a single radioactive compound. This compound was shown to be S-succinyl-L-cysteine by paper chromatography (two solvent systems), paper electrophoresis, and column chromatography with an amino acid analyzer. Free radicals are known to be created during dough mixing, and the effect of fumaric acid can be stopped by free radical scavengers. Thus a logical assumption is that fumaric acid reacts by a free radical mechanism. The finding that fumaric acid reacts with gluten protein more readily than with soluble proteins to form S-succinyl protein derivatives suggests the disulfide bonds as the site of the free radical formation. Further supporting the hypothesis, potassium iodate, which is known to react with free sulfhydryl groups, did not materially reduce the incorporation of 14C-fumaric acid into gluten proteins. Thus fumaric acid reacts with a free radical formed by the cleavage of a disulfide bond in the gluten proteins.