Iiimportance To Quality Of Food

LOX is known to have several detrimental effects in foods (see reviews: 36, 37), and these effects can be controlled by various methods of enzyme denatura-tion. By the process of cooxidation by free radicals, LOX activity is known to cause bleaching of carote-noids, chlorophyll (38, 39, and Refs. therein), and oxidation of ascorbic acid (40). LOX probably accounts for a large portion of pigment bleaching and loss of quality observed in unblanched frozen vegetables. In addition, products of LOX action, fatty acid hydroperoxides, are cleaved both enzymically and nonenzymi-cally into odorous shorter-chain aldehydes, alcohols, and alkanes. The nonenzymic formation of odors is very detrimental leading to complex free radical products broadly defined as "rancidity" (see review: 41). LOX reactions can even occur in "dry" substrates at the lowest relative humidities examined (52%) (42). It was also demonstrated that LOX action in dry substrates initiated free radical autoxidation of polyunsa-turated fatty acids.

Although LOX is often considered to be detrimental to foods, there are examples of positive uses. LOX has been used in replacing bromates to improve dough elasticity for bread making presumably by increasing disulfide bonds through oxidation (see review: 43). In addition, LOX bleaches carotenoid through cooxida-tion in doughs increasing the whiteness of bread. As discussed below, the LOX/hydroperoxide lyase sequence, also involving other enzymes such as alcohol dehydrogenase and double-bond isomerase, is important in imparting odors and flavors to fresh fruit and vegetables. These flavors are important enough to persuade Firmenich to develop an enzymic procedure for their biosynthesis (44).

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