Vegetable oils oxidative deterioration

Oxidation. Oxidation of oils and fats is due to prolonged exposure to air. By virtue of the low polyunsaturated fatty acid content, palm oil is relatively more stable to oxidative deterioration than the polyunsaturated vegetable oils. However, in the presence of trace metals such as iron and copper, excessive oxidation at the olefin bonds of the oleic and linoleic acids can occur, resulting in rancidity. Highly oxidized crude palm oil is known to have poor bleachability and thus requires more bleaching earth and more severe refining conditions, and the final product will likely be of poor stability (44, 45, 68). 

Sesame oil contains high levels of unsaturated fatty acids (more than 80% of total fatty acids) however, it is highly resistant to oxidative deterioration as compared with other edible vegetable oils (39, 40). The superior oxidative stability is not... 

The tocopherols and tocotrienols are generally not the major components of vegetable oil, but their presence is vital for stabilizing the unsaturated fatty acids of these oils against oxidative deterioration (39). Their structures are based on a chroman head with two rings, one phenolic and one heterocyclic, and a phytyl tails isoprenoid side chain at C-2. The phytyl tail is saturated in the case of... 

Deterioration of food lipids by fi ee radical chain reaction and lipid peroxidation is a major problem for food manufacturers. The main route of deterioration of vegetable oils is rancidity deriving fi-om the oxidation taking place at the insaturation sites of the fatty acids in the triglyceride molecules. In general the higher the number of double bonds, the easier is... 

Various gas chromatographic (GC) methods, such as direct injection, dynamic headspace, and static headspace, have been used for the analysis of volatile products, resulting from the oxidative deterioration of vegetable oils. Though advantages and disadvantages are apparent with each GC method, for routine analyses, static headspace is the method of choice because it is rapid and requires no cleaning between samples. ... 

Tan, C.P. and Man, Y.B.C. Recent developments in differential scanning calorimetry for assessing oxidative deterioration of vegetable oils. Trends Food Sci. Technol. 13, 312-318 (2002). 

Antioxidants such as a-tocopherol, ascorbic acid and tea catechin can effectively inhibit the oxidation of vegetable oils and development of rancidity in food lipids. However, it has been difficult to protect fish oils containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) against oxidative deterioration and an effective antioxidant method for fish oils is required. As shown in Figure 5, oxidation of ethyl DHA was completely inhibited in the cathodic solution, although it was more easily oxidized in distilled water or in the NaCl solution, therefore, the cathodic solution may be useful as an effective antioxidant for fish oils. 

CLN has three double bonds as same as LN. However, CLN is more easily oxidized than LN to prodnce polymers as the main oxidation products (Suzuki et al., 2004). This oxidation proceeds via free radical chain reaction and the radicals formed initiate the oxidation of PUFA in vegetable oils. Thus, CLN acts as an oxidation inducer as well as flavour reversion precursor. Canola oil contains relatively lower CLN as compared with other vegetable oils (Table 16.1), indicating that canola oil is stabler than oxidative and flavour deterioration. 

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