Fatty acids oxidation, peroxidation

As shown in Table (2), vegetable oils contain variable levels of unsaponifiable matter (3) of variable composition and characteristics (4). The refining process, which is necessary to remove undesirable pigments and fatty acid oxidation products such as peroxides and their degradation products from vegetable oils to make them suitable for consumption, unfortunately, brings about loss of valuable nutrients and natural antioxidants (5-7). The technical and nutritional importance... 

A peroxisome proliferator is a chemical that induces peroxisome proliferation in rodent liver and other tissues and includes a wide range of chemicals such as certain herbicides, plasticizers, drugs, and natural products [38,39], The peroxisomes contain hydrogen peroxide and fatty acid oxidation systems important in lipid metabolism and activation of the peroxisome proliferator-activated receptor alpha (PPARa), is considered a key event in peroxisome proliferation in rodent hepatocytes [39], A number of studies have identified... 

The PPARa Activator MOA Is Chemical-Independent. Mode of action is a series of key events that together result in an adverse health effect such as a liver tumor and as such is chemical-independent (Boobis et al. 2008 Holsapple et al. 2006 Meek 2008). Consistent with this the MOA for PPARa activators is an endogenous series of events that can occur independent of chemical exposure. Livers from ACO-nuU mice exhibit severe steatosis, increases in markers of PPARa activation (i.e., genes involved in P- and co-fatty acid oxidation), increases in hydrogen peroxide levels, increases in ceU proliferation and fiver tumors (Fan et al. 1998). The increases in the markers of PPARa were shown to be PPARa-dependent as the changes were abolished in a double ACO-/PPARa-null mouse (Hashimoto et al. 

Palatability is a combination of many qualities, such as taste, aroma, mouth feel, and ingestive behavior of pet foods. Raw materials and the formula have a significant impact on palatability hence, producers should be careful to select ingredients and recipe in order to produce high-quality and high-yield dry pet foods. Fats, which are one of the main ingredients, should be low in free fatty acids and peroxide contents to prevent or reduce rancidity, which would lead to a dramatic loss in the palatability of pet foods. Various antioxidants could be added to prevent oxidation reactions in pet foods. 

Oxidation of polyunsaturated fatty acids (PUFA) in lipoproteins may be mediated by reactive species such as radicals, transition metals, other electrophiles, and by enzymes. Once initiated, oxidation of lipids may proceed by a chain reaction, illustrated in Fig. 4 (R5). In step I, an oxidant captures an electron from a PUFA to produce a lipid radical. In step 2, after rearrangement, the conjugated diene radical reacts rapidly with singlet oxygen to produce a lipid peroxide radical, which is the kinetically preferred reaction (step 3) (B5). The chain can be terminated if the lipid radical reacts with an antioxidant to produce a stable peroxide (step 4). Otherwise, the peroxyl radical can react with another polyunsaturated fatty acid as shown in step 5 to perpetuate a chain reaction. The chain reaction requires production of lipid peroxides, giving it the name peroxidation. Fatty acids oxidized in the core are largely triglycerides and cholesterol esters, while toward the outer layer fatty acids in phospholipids are oxidized. 

The variety of aldehydes, ketones, peroxides, and other oxidation products of fatty acid oxidation will depend on the structures of the fatty acids and on the extent of oxidation. Table 1 lists some products that have been measured, the predominant fatty acid from which the product is derived, and common methods used for measurement. Measurement of these oxidation products has been considered specific or nonspecific, depending on the purity of the product measured and the specificity of the method used. It is also useful to know from which fatty acid which product is predominately produced. 

The effects of zinc oxide, fatty acids, and peroxides is described in more detail by Rothemeyer and Sommer [32]. 

With the main exception of some nonenzymatic peroxidation reactions on oils or membrane lipids (in which total lipid oxidation is involved), most areas of acyl lipid oxidation in plants are concerned with the fatty acid components, either as free fatty acids or as activated thioester forms. Lipid peroxidation reactions are outside the scope of this chapter but are covered by Galliard and Chan (this volume, Chapter 5). The following discussion will relate mainly to fatty acid oxidation. 

Toasting of soybeans by heating at 100-1 lO C to inactivate lipoxygenase and antinutritional factors (e.g. trypsin inhibitor) is important to improve the quality of soybean protein products used for either animal feed or human consumption. However, this thermal enzyme inactivation is not carried out in the conventional processing of soybean oil. Therefore, the soybean flakes must be solvent extracted without delay to minimize free fatty acid and peroxide formation in the extracted crude oil and to produce a finished oil of improved oxidative and flavor stability. 

The high stability of the macadamia nut oil may be associated with the storage conditions and the xmsaturated fatty acid profile, which is an important factor since the unsaturations make the oil less susceptible to oxidation. Therefore, macadamia nut oils have high oxidative stability due to the high content of monounsaturated and polyunsaturated fatty acids. Low peroxide and acidity values are also responsible for high oxidative stability since they are associated with the quality standards and conservation of raw materials [28]. 

When wholemeal flour is mixed with water, dissolved oxygen is consumed due to a lipoxygenase-catalysed peroxidation of F-puFA . The fatty acid oxidation products that are formed in low amounts in aqueous suspensions of white flour have been described previously. This paper illustrates the more substantial lipid peroxidation reactions that occur in aqueous suspensions and doughs of wholemeal flour and points out several important practical implications of this process. 

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