Oxidation



1. How can I replace potassium bromate, azodicarbonamide or ascorbic acid?
The replacement of potassium bromate requires an oxidizing agent, e.g. ADA or ascorbic acid, and an enzyme that helps to soften the dough. The fast-reacting ADA can be replaced by mixtures of calcium peroxide and ascorbic acid. Ascorbic acid can only be omitted (in the absence of any other oxidizing agent) if limitations to baking performance are tolerated. Oxidizing enzymes such as glucose oxidase are not very effective in the centre of the dough unless the mixing process is performed at elevated air pressure or with the introduction of oxygen into the dough.

2. Why does benzoyl peroxide not succeed in bleaching my chappati flour (flour for flat bread, very high extraction rate)?
Various explanations are possible :
a. The dark colour of wholemeal flour is not only due to carotenoids with which benzoyl peroxide reacts.
b. Because of the high concentration of pigments the BPO is exhausted before it achieves a brighter colour.
c. The benzoyl peroxide was premixed with flour and stored for more than just a few hours. This results in a partial or even complete reaction with the carrier, but not with the main flour.
d. The dark colour is partially caused by foreign substances, e.g. metal debris from the rollers or fortifying agents containing dark substances.

3. Why does ascorbic acid turn yellow during storage, and does that affect its efficiacy as an oxidizing agent in flour?
It used to be assumed that this is due to the formation of an oxidized form of dehydroascorbic acid (DHA). But for two reasons this is probably not the case : a) no DHA is detectable in yellow acorbic acid, and b) DHA forms white crystals. But there is some likelihood that DHA is just an intermediate product, because it is not very stable and converts into some unknown substances that are first yellowish and then brown when exposed to air. Whatever the reaction is, it does not affect the function of the ascorbic acid in baking, probably because the degree of degradation is very small.

4. Can ADA added to my flour trigger a positive result when the flour is tested for nitrofurans?
Yes, Nitrofuran metabolite residues (semicarbazides, SEM) were initially discovered in pigs, pultry and shrimps. They are formed as a tissue-bond residue following the administration of nitrofurazone, a banned antibiotic. However, SEM has also been found to occur in materials used for coating chicken meat in the production of cooked chicken products. Most positive findings have been associated with the use of either carrageenan or breadcrumbs (and other bread products). A subsequent investigation revealed that azodicarbonamide can break down during the bread making process to yield SEM, which is responsible for the positive nitrofuran results.

5. Is it feasible to prepare premixes of benzoyl peroxide and wheat flour?
A premix of benzoyl peroxide (BPO) and flour should be used immediately after preparation. Otherwise BPO reacts with the flour of the premix, sometimes resulting in off-flavour due to excessive oxidation, and no activity will be left for the main flour stream. A premix should be prepared with (almost) inert substances, e.g. calcium sulphate, calcium carbonate, or starch. Soybean flour, in particular full-fat soybean flour, is least suitable because the BPO will oxidize the lipids, causing severe off flavour.

6. How does chlorination affect the properties of biscuit flour and products made from it?
Chlorination does not only brighten the flour by oxidizing the pigments contained in it; it also oxidizes proteins and pentosans. Since biscuit flour contains little protein, and what it does contain is weak, oxidation of the protein (formation of disulphide bridges) has scarcely any effect on the baking properties. But oxidation of the water-soluble pentosans appears to have an effect on the foam stability of whipped masses and thus the structure of the baked products. In the case of heavy masses (high-ratio cake), especially, this results in much better volume and a finer texture. At present chlorinated flour can only be replaced to a very limited extent by thermally treated flours.

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