Oxidation indices peroxide value

In this chapter an environmental friendly extraction process of com germ oil based on the use of supercritical CO2 (SC-CO2) is presented. The effect of important operating parameters in supercritical fluid extraction (SEE) processes such as pressure, temperature and flow rate on the extraction kinetics and the quality of the extracted oil is discussed. As for many SC-CO2 extractions of vegetable oils, extraction curves of com germ oil present an initially linear part with a slope close to the oil solubility value in CO2. Then, a second section of the extraction curve is determined by the diffusional resistance in the solid matrix. Characterization of supercritical cmde com oil is presented by showing some properties reported in the literature such as physical parameters, fatty acid composition, neutral lipids, content of tocopherols, acid index, peroxide value, antioxidant capacity and the oxidative stability. 

Active Oxygen Method for Fat Stability (AOM) (Cd 12-57) determines the time (in hours) for a sample of fat or oil to attain a predetermined peroxide value (PV) under the conditions of the test. The method is used to estimate the comparative oxidative stability of fats and oils. The method has been placed in surplus, in favor of Cd 12b-92 (Oil Stability Index), but retains official status and is still used in domestic industry. p-Anisidine Value (AV) (Cd 18-90) determines the amount of aldehydes (principally 2-alkenals and 2,4-dienals) in animal and vegetable fats and oils. These are degradation products of peroxides, which are not removed by bleaching. Some fats and oils chemists propose increased use of this method in purchase specifications. Bleaching Test for Soybean Oil (Cc 8e-s63) determines the color of a sample of soybean oil after treatment with a specified bleaching earth. Specific methods exist for other oil species. 

Peroxide value, expressed as milliequivalents of peroxide per kilogram of oil, measures the primary oxidation products of oils— the hydroperoxides. The peroxide value has shown a particularly good correlation with sensory flavor scores of soybean oU, and its use during storage is quite common. The peroxide value is an index to the oxidative state of an oU. Soybean oU is considered fresh with a peroxide value <1.0 mEq/kg, to have low oxidation with 1.0-5.0 mEq/kg, to have moderate oxidation at 5.0-10.0 mEq/kg, to have high oxidation at > 10.0 mEq/kg, and to have poor flavor quality at >20 mEq/kg (6). Several methods (300-303) can be used to measure the peroxide value of an oil depending on the specific circumstance. 

Refractive index, iodine value, AOM stability, and peroxide value provide standardized methology for those factors affecting oxidative stability (5, 113). 

Lipid hydroperoxides can be measured by peroxide value (PV) and 2-thiobarbituric acid (TBA) tests. The resistance of a fat or an oil to oxidative rancidity can be measured by the Schaal oven test, Swift test, and oil stability index (OSI) analysis. 

Wang and Johnson (2001) reported on test measurement methods that were major indicators of soybean oil quality. These tests included peroxide value, anisidine value, FFA content, phospholipid content, total tocopherol content, oxidative stability index, color, and moisture content. For soybean meal, they reported on urease activity, protein dispersibility index (PDI), rumen bypass or rumen undegradable protein, trypsin inhibitor activity, moisture content, residual oil content, protein content, fiber content, color, amino acid profiles, and protein solubility under alkaline (KOH) conditions. 

The peroxide value is a normal oxidation index, which has to be carefnUy used because at high temperatures, hydroperoxide decomposition may be more rapid than formation thns, degradation is not reflected by this index. 

Among the most common methods to measure thermal and oxidative behavior of oils are the classical oxidative stability analysis used by industries, based on the active oxygen method (AOM), which determines the number of hours required for the oil to reach a peroxide value of 100 meq/kg O and the oxidative stability index (OSI), which can be considered as automated AOM with an apparatus that simulates the events under specific atmospheres, usually with the use of high temperatures. The OSI method measures the changes in water conductivity when the oxidation compounds are formed [17]. 

Other parameters that are usually determined to assess the oil stability and quality are the acid index (Al) and the peroxide value (Ca 5a-40 and Cd 8-53 AOCS Methods). The oxidative stability is also an important parameter in the characterization of fats and oils that can be determined among other methods by using the Rancimat test. 

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