Carotenoids 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. 

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). 

The ability of LOX to catalyze cooxidation reactions has long been recognized (e.g., its carotene oxidase activity see Section I) and has been used as the basis for some LOX assays (see Section IV) and in commercial applications e.g., soybean or Vida faba flours (both rich in LOX activity) are added to bleach wheat flour pigments in white bread production. Cooxidation is clearly manifested in the bleaching of pigments (chlorophyll, carotenoids, etc.) but also results in the oxidation of protein-SH groups and of unsaturated fatty acids, including substrates for LOX. 

Lipoxygenase catalysed processes. Enzymatic bleaching of wheat flour by lipoxygenases is a widely practised operation in Europe and North America. The process is due to co-oxidation of carotenoids during oxygenation of polyunsaturated fatty acids such as linoleic acid to hydro-peroxy-octadecadienoic acid (Hildebrand and Hymowitz, 1982 Nicolas et al., 1982). The hydro-peroxy-octadecadienoic acids (HCDs) are key intermediary compounds for the synthesis of other important... 

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