Bleaching wheat flour

The presence of lipoxygenase in plants may affect their storage and processing since it promotes the peroxidation of the polyunsaturated fatty acids (which are nutritionally essential) and can affect taste, odor, and color. Moreover lipoxygenase may influence ripening and abscission. In fact, it has been used to modify fatty acids, to bleach wheat flour, and to improve the rheological properties of wheat dough. An excellent dis-... 

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 Enzyme that oxidizes lipids and lipophilic pigments, carotenes and xanthophylls, by incorporating oxygen in double bonds yielding hydroperoxides and peroxides that later on decompose into many chemical compounds (organic acids, aldehydes, ketones, alcohols). These enzymes, generally supplemented with full-fat soybean meals, are still used to bleach wheat flours. 

Benzoyl peroxide is used as a bleaching agent in wheat flour, but its more familiar use is as a powerful acne medication that can lay claim to the following benefits ... 

Wheat flour typically becomes white by means of normal oxidation in air during a few weeks of storage. To speed up the process, manufacturers use benzoyl peroxide as a bleaching agent. Sulfur dioxide is a reducing bleaching agent that is used to preserve dried fruits. 

Unheated pea flours are also effective in bleaching and improvement of doughs (37,31). Mixing times are shorter with pea-wheat flour combinations, and mixing tolerance is increased. 

Benzoic acid is a by-product of benzoyl peroxide used in the bleaching of freshly milled wheat flour. A maximum benzoic acid concentration of 16 ppm was reported after 12 h of bleaching. The concentration decreased to 6 ppm after 3 months (Saiz et al., 2001). 

In sophisticated areas, milled wheat flour is artificially aged and bleached, and chlorine dioxide is now preferred as the bleaching agent. Using the paper chromatography method, Moore et al. (1957) observed that 80% of the tocopherols in flour were destroyed when 30 parts per million (ppm) of chlorine dioxide were used to bleach. Later, they confirmed this result by hemolysis tests and rat assays (Moore et al., 1958). 

NFPA Health 3, Flammability 0, Reactivity 1 Uses Flour treatment agent, bleaching agent for flour, whole wheat flour Regulatory FDA 21CFR 137.105,137.200 SARA 302/304/313 nonregulated, 311/312 acute, reactive, and sudden release hazard... 

Lipoxygenases will also catalyse co-oxidation reactions. This is used both in assay methods for the enzyme and in commercial applications. An example of the latter is the addition of soybean or broad bean flours (both rich in lipoxygenase activity) to wheat flour in order to bleach pigments for white bread production. Enzymes from different sources differ in their co-oxidation ability, e.g. soybean type-I enzyme has poor activity in this regard while soybean type-II enzyme has high co-oxidation activity. The reaction probably proceeds by a free-radical process (Veldink et al., 1977) and requires the presence of a substrate (e.g. linoleic acid) as well as the co-substrate. The extent of the cooxidation may depend on the lifetime of the radical intermediates and the relative efficiency of the lipoxygenase-mediated radical reduction (Weber and Grosch, 1976). 

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... 

Floui. There are myriad types of flour, made from many grains from around the globe, but in the US, the most common is wheat flour. That category can be further broken down into enriched, blended, whole grain, bread, graham, bolted, cake, bleached and unbleached, and so on. Overwhelmed Start with all-purpose flour, sold inexpensively at any supermarket in variously sized bags. And there you have your cornerstone. 

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... 

Refined soft wheat flours treated with chlorine. Chlorination breaks disulfide bonds, weakens the gluten, lowers pH, and bleaches the flour. Hours usually contain from 7.5% to 10% protein and, upon hydration and mixing, yield weaker gluten doughs compared to regular soft flours. 

Chlorinated flour Wheat flour that has been treated with chlorine for aging and bleaching purposes. The flours that are most frequently chlorinated are cake flours. These bleached flours have an acidic pH and weaker gluten due to disruption of disulfide bonds. 

Almost any type of flour can be made as a wholemeal in principle. Wholemeal flour is what it says it is, i.e. all of the wheat. It is illegal to bleach fortify or add flour treatments to wholemeal flour. It is the only type of flour that does not have to be fortified as the natural minerals that were present in the wheat are all present in wholemeal flour. The wheat germ oil is also present. 

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