Flour, Thiols

Adding antioxidants to the defatted soy flour prior to alkaline extraction enhances the solubility of the protein isolate in proportion to the decrease in oxidation of thiol groups (Boatright and Hettiarachchy, 1995). 

The ascorbic acid is oxidized by ascorbic acid oxidase in the flour dough to dehydroascorbic acid. In turn, the reduction of dehydroascorbic acid is coupled with the oxidation of protein thiol groups by the enzyme dehydroascorbic acid reductase known to be in wheat (133). 

Besides charcoal, ancient enology treatises mention other products likely to eliminate unpleasant smells and off-flavors toasted barley or wheat, mustard flour, oil, milk, etc. All these have practically disappeared from use. Fresh yeast lees are permitted in treating wine and are effective in eliminating a number of olfactory defects. This has already been mentioned in connection with fixing certain thiols, such as methanethiol (Section 8.6.2). This treatment is also recommended for adsorbing chloroanisoles in moldy wines (Section 8.5.2). 

Our results show that thiols and sulfites, which also cleave disulfide bonds, make it possible to lower protease inhibitor content of soybean flour to near zero levels. The accompanying improvement in nutritional quality as measured by rat feeding studies may result from one or more of the following events (a) inactivation of inhibitors of digestive enzymes (b) improvement in digestibility of the soy and... 

The described cooperative action of thiols probably involves sulfhydryl-disulfide Interchange or oxidation-reduction reactions between added thiols, native inhibitor disulfide bonds and, in the case of flours, disulfide and sulfhydryl groups of the other proteins present, as illustrated ... 

Mercurimetric methods have no advantage over the argentimetric methods for the titration of cysteine, but they are more suitable for the determination oiglutathione The method has been used for the determination of soluble thiols in flour,... 

Table 15.24. Occurrence of low-molecular thiols in wheat flour ...

Although lipoic acid has been found in numerous biological tissues, reports on its concentrations in foods are scarce. Lipoic acid is detectable in wheat germ (0.1 ppm) but not in wheat flour. It has been detected in bovine liver kidney and skeletal muscle. Oral administration of lipoic acid (1.65 g/kg fed) to rats for five weeks resulted in elevated levels of the thiol in liver, kidney, heart, and skin. When lipoic acid was added to diets lacking in vitamin E, symptoms typical of tocopherol deficiency were not observed suggesting that lipoic acid acts as an antioxidant in vivo. However, lipoic acid was not capable of recycling vitamin E in vivo, as determine by the fact that a-tocopherol concentrations are not elevated by dietary lipoic acid in vitamin E deficient rats. 

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