Rancidity, peroxidation causing

However, the ability to act as a builder encompasses much more than so far been mentioned. Builders influence the coagulation of solid soil, often form a buffer system, and promote the soil suspending activity of washing liquors. They are further able to reduce the catalytic effect of ferric and manganic ions. Thus they support the stabilization of peroxides in detergents. Similarly, rancidness caused by catalytic processes of soap and fragrances can be avoided. 

Powdered aluminium had been added to oleic acid. The mixture detonated after being prepared. Such an accident could not be repeated and it was thought that it was caused by the presence of a peroxide formed by the effect of air on oleic acid. In fact, the acid functional group has obviously nothing to do with the peroxidation. It is more likely that the chain s double bond that activates p hydrogen atoms (ally position) was involved in it. This is a well-known phenomenon since it is responsible for the rancidity of some oils and greases. 

Oxidation is also the main cause of perfume instability in poor-quality toilet soaps here it is caused by the fatty acid peroxides formed at the stage of incipient rancidity. Perfumes may to some extent be protected against oxidation by the incorporation of 1% to 2% of an antioxidant such as BHT (butylated hydroxy toluene) into the perfume oil. 

There are many different kinds of reactive metabolites which it is beyond the scope of this book to discuss. However, one type is particularly important. This is the free radical, and the important feature of these is that on reacting with another chemical another free radical is produced, a so-called chain reaction. This leads especially to the destruction of fats and the membranes of which they form part. In the presence of oxygen this causes a destructive process call lipid peroxidation. A similar process causes butter to go rancid. 

The development of a characteristic, objectionable, beany, grassy, and hay-like flavor in soybean oil, commonly known as reversion flavor, is a classic problem of the food industry. Soybean oil tends to develop this objectionable flavor when its peroxide value is still as low as a few meq/kg, whereas other vegetable oils, such as cottonseed, com, and sunflower, do not (15, 51). Smouse and Chang (52) identified 71 compounds in the volatiles of a typical reverted-but-not-rancid soybean oil. They reported that 2-pentylfuran formed from the autoxidation of linoleic acid, which is the major fatty acid of soybean oil, and contributes significantly to the beany and grassy flavor of soybean oil. Other compounds identified in the reverted soybean oil also have fatty acids as their precursors. For example, the green bean flavor is caused by c/i-3-hexenal, which is formed by the autoxidation of linolenic acid that usually constitutes 2-11% in soybean oil. Linoleic acid oxidized to l-octen-3-ol, which is characterized by its mushroom-like flavor (53). 

Peroxide Value. Oxidation of oils is a major cause of their deterioration. Hydroperoxides are the primary products formed by the reaction between oxygen and the unsaturated fatty acids. Hydroperoxides have no flavor or odor but break down rapidly to form aldehydes, which have a strong, disagreeable flavor and odor. The peroxide concentration, usually expressed as peroxide value (PV), is a measure of oxidation or rancidity in its early stages. PV measures the concentration of substances, in terms of milliequivalents of peroxide per 1000 grams of sample, that oxidize potassium iodide to iodine. AOCS Method Cd 8-53 (103) is the official method for peroxide value determinations. 

The reaction proceeds until the free radicals are destroyed by inhibitors or by side-reactions which eventually break the chain. The rancid odour which is a characteristic of oxidised fats and oils is due to aldehydes, ketones and short-chain fatty acids which are the breakdown products of the hydroperoxides. Peroxides (ROOR ) and hydroperoxides (ROOH) are photolabile, breaking down to hydroxyl (HO ) and/or alkoxyl (RO ) radicals, which are themselves highly oxidising species. The presence of residual peroxides in polyoxyethylene glycols (PEGs) is a cause for concern when these excipients are used in formulation, as for example in the case of fenprostalene. ... 

It was observed wth the Flake Yeast diets that fat tissue in which e.xudate had formed contained no peroxide detectable by the iodometric method in 19 out of 23 cases. This su ests that the in vivo peroxidation of body fat usually observed in exudative diathesis produced by casein and cod liver oil diets, and to a lesser degree by Tonda yeast diets, is not per se the cause of the exudation process, but a sign of the disappearance of the antioxidant vitamin E from tissue suppUed with polyenoic fatty acids. The destruction of vitamin E by polyunsaturated fatty acids proceeds before rancidity products accumulate, namely by interaction of vitamin... 

Preparation and storage of products from both oilseeds is often inhibited by rancidity and bitter aroma defects caused mostly by volatile aroma active carbonyl compounds, e. g., (Z)-3-hexenal, (Z)-l,5-octadien-3-one and 3-methyl-2,4-nonan-dione. The rancidity-causing compounds are formed through peroxidation of linolenic acid, accelerated by the enzyme lipoxygenase and/or by hem(in) proteins (cf. 3.T.2.2). Furan fatty acids are the precursors in the case of the dione (cf. 14.3.2.2.5). Lipid peroxidation is also involved in the formation of another very potent odorant, 2-pentylpyridine, which produces grassy aroma defects in soybean products. Defatted soybean protein isolates contained 60-510 pg/kg of this compound, which with an odor threshold... 

Ethers are a laboratory hazard because they form explosive peroxides by reacting with O2 when they are exposed to air. We will see that this reaction is similar to the reaction that causes fats to become rancid (Section 13.11). 

Unsaturated fatty acids are prone to undergo oxidation and form oxides and peroxides which cause rancidity and yellowing. 

Lipid peroxidation occurring in food products causes some deterioration in food quality such as rancid flavor, bad taste and shortening of shelf life. The intake of oxidative foods is thought to cause serious diseases such as enlargement of liver (I) or necrosis of epithelium tissue. The factors involved in these diseases were lipidperoxidants and low-molecular conqjounds produced at the latter stage of oxidative reaction (2). Furthermore, cancer, coronary heart diseases and Alzheimer s diseases were also reported to be partially responsible for oxidation or free-radical reaction (5-6). In order to prevent foods from these deterioration and prevent us from serious diseases, it is very inq>ortant to inhibit... 

Oxidative rancidity Chemieal reaetion in which the double bonds of fatty acids are oxidized to form peroxides, which eventually decompose into aldehydes, ketones, and alcohols. These decomposition products cause off-flavors, odors, and rancidity. Two types of rancidities are known enzyme-mediated and autooxidation. 

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