Oxidation and Flour Maturation

8. Chlorine and Chlorine Dioxide
These oxidizing agents have been banned in many countries because of their possible harmful effects on health and the technical risks they involve. There is no doubt that with certain baked goods (for example cake with a high proportion of fat and sugar) chlorination of the flour – that can only be carried out at the mill – produces the best results. Products: Cl2, ClO2 (typical dosage 20 - 250 ppm), hypochlorite (NaOCl, Ca(OCl)2)

Chlorine reduces the pH because it is converted into hypochloric acid through reaction with water according to the following equation:
Cl2 + H2O → HCl + HClO.
The pH usually drops to 4.5 - 4.7, and in flour for certain cookie applications it even falls as low as 3.5. But the acidity is not responsible for the improving effect, since the latter is retained even after neutralization (Kulp et al., 1985).

The resulting hypochloride is a strong oxidant, reacting with flour pigments and other components. ClO2 is a green gas that dissolves in water. It does not react with water, but with unsaturated chemical bonds and other reducing groups. Chlorine and its derivatives affect pigments (bleaching), starch (partial breakdown of amylose and amylopectin that alters the pasting properties), proteins (improved solubility), fats (saturation) and pentosans (degradation, and hence reduced water absorption) (Kulp et al., 1985).

Heat-treated flours have a certain similarity to chlorinated flour when combined with wheat starch, but chlorinated flour still achieves much better results (Seibel et al., 1984).

9. Calcium Peroxide
Calcium peroxide is yet another commonly used oxidizing agent. Upon heating, CaO2 releases oxygen that can be used in various oxidation reactions, for instance oxidation of ascorbic acid or water to hydrogen peroxide with the help of glucose oxidase. The effect of calcium peroxide is not very pronounced, but it is appreciated for its surface-drying property. For this reason it is always used in conjunction with more effective oxidizing agents. Calcium peroxide increases the pH of the dough. In certain limits this can be beneficial, particularly if the flour has high amylase activity. Larger amounts reduce the volume yield and cause excessive browning.

10. Other Oxidizing Agents
Tab. 86 summarizes the oxidizing agents that have been suggested for use in flour improvement. The "action in the dough" is based on the author's experience. For some of the substances, different information can be found in the literature. Some substances are rather risky, for instance acetone peroxide that tends to explode when exposed to even slight shock or friction. The substances not mentioned in the text above do not offer any considerable benefit as compared to the standard oxidizing agents.

Tab. 86: Oxidizing agents suggested for flour treatment, and their typical reaction pattern


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