Wheat flour lipoxygenase

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 importslnce of lipoxygenase increases when soybean flour is added to wheat flour to improve baking quality or when soybean flour is admixed in larger quantities to improve the protein nutritional quality. 

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... 

The involvement of endogenous lipoxygenase in the baking of wheat flour is not clear. However, by addition of lipoxygenase-active soy flour, a significant improvement of the flour quality is achieved (cf. 15.4.1.4.3). 

Fig. 15.35. Wheat flour quality improvement by the nonspecific lipoxygenase enzyme of soybean (according to Kieffer and Grosch, 1979). Additions 1 control (no addition, bread volume 31 ml), 2 extract of defatted soya meal in which lipoxygenase was thermally inactivated (31 ml), 3 extract of a defatted soya meal with 290 units of lipoxygenase (35 ml), 4 purified type-II enzyme with 285 activity units (37 ml).

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. 

Wheat lipoxygenase and soybean lipoxygenase, catalyzing oxidation of fatty acids, generate oxidized reaction products that improve the dough-forming properties and baking performance of flour. A similar role is performed by polyphenol oxidase and peroxidase. 

This enzyme oxidizes linoleic and linolenic acids rapidly in whole flour or milling products containing wheat germ or bran mixed with water. The initial hydroperoxides formed by lipoxygenases in stored wheat bran are converted to secondary products, mono- and trihydroxy fatty acids. These oxidation products causing bitter and rancid flavors are formed in higher concentrations in hydrated products than in dry raw materials. Rancid flavors develop rapidly on hydration. 

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