Flour bleaching

Flour Bleaching Agents and Bread Improvers. Freshly milled flour contains carotenoid pigments that cause the flour to have a yellow color. In addition, when the flour is made into dough the product is sticky and unmanageable. As the flour ages, a natural process takes place which turns the flour white and improves its baking qualities. Because the natural process takes quite a bit of time, additives are used to speed up the process. 

An explosion in flour-bleaching operations was attributed to violent decomposition of the basic nitrate [1], which is an impact-, friction- and heat-sensitive explosive [2]. The instability is associated with the presence of reducant and oxidant functions in the same molecule. The previous formulation as tin(II) nitrate oxide is revised to that above. 

Thus, flour bleached with chlorine dioxide contains little or no tocopherol. On the other hand, no measurable loss occurs when similar white flour is bleached using ascorbic acid or potassium bromate (Moore et al., 1957). 

The non-specific lipoxygenases can cooxidize carotenoids and chlorophyll and thus can degrade these pigments to colorless products. This property is utilized in flour bleaching (cf. 15.4.1.4.3). The involvement of LOX in cooxidation reactions can be explained by the possibility that the peroxy radicals are not as rapidly and fully converted to their hydroperoxides as in the case of specifically reacting enzymes. Thus, a fraction of the free peroxy radicals are released by the enzyme. It can abstract an H-atom either from the unsaturated fatty acid present (pathway 2a in Fig. 3.30) or from a polyene (pathway 2b in Fig. 3.30). 

Table 11.14 Chlorinated fatty acids in flour bleached with chlorine.

Azodicarbonamide is used as a blowing agent in the plastics industry. Moreover, it is used as a food additive, not - as may be suspected - as a yeast replacement, but as flour bleaching agent. However, in some countries its use as food additive is not allowed. 

The Br value of human blood lies between 227 and 572 y per 100 ml., the average being 372 y for blood, and 656 y for urine (Conway and Flood, 1936). Impure table salt, baking powder, and the hypochlorite used in flour bleaching are common sources of bromine in the diet. (l,000y = 1 mg.). 

Flours are commonly treated with additives and enrichment premixes to standardize quality and meet regulations. The treatments commonly consist of flour bleaching, maturing or aging, enzyme supplementation, and addition of the enrichment to supplement selected minerals and vitamins. Hard wheat flours are, in some instances, oxidized with azodicarbonamide, ascorbic acid and/or, in some countries, with potassium bromate in order to improve functionality. Soft wheat flours are in some instances chlorinated to produce bleached cake flours. The normal range of chlorination ranges... 

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