Secondary oxidation products anisidine value

Secondary oxidation products oxidation indices, 656, 665-72 acid value, 672 anisidine value, 656, 666 carbonyl compounds, 656, 669-71 conjugated dienes value, 671-2 thiobarbituric acid reactive substances, 656, 666-9... 

Although the work just described used canola oil, similar increases in free fatty acid levels as a consequence of higher bleach temperatures have been reported for soya (118) and pahn (86, 119) oils. The latter workers also reported decreased peroxide values but increased anisidine values as bleach temperature was increased. This conforms to expectation because the anisidine test is diagnostic for shorter chain aldehydes (including alkenals and dienals), which are secondary oxidation products of peroxide decomposition. 

Carbonyl compounds in oxidized lipids are the secondary oxidation products resulting from the decomposition of the hydroperoxides. They can be quantified by the reaction with 2,4-dinitrophenylhydrazine and the resulting colored hydrazones are measured spectrophotometrically at 430-460 nm. The carbonyl value is directly related to sensory evaluation, because many of the carbonyl molecules are those responsible for off-flavor in oxidized oil. The anisidine value is a measure of carbonyl compounds that have medium molecular weight and are less volatile (Frankel 1998). It can be used to discover something about the prior oxidation or processing history of an oil. 

AOCS has a recommended practice (Cg 3-91) for assessing oil quality and stability (AOCS, 2005) for measuring primary and secondary oxidation products either directly or indirectly. For example, peroxide value analysis (AOCS method Cd 8-53) (AOCS, 2005) determines the hydroperoxide content and is a good analysis of primary oxidation products. To determine secondary oxidation products, the procedure recommends p-anisidine value (AOCS Method Cd 18-90, 2005) volatile comlb by gas chromatography (AOCS Method Cg 4-94, 2005) and flavor evaluation. (AOCS Method Cg 2-83, 2005). The anisidine value method determines the amounts of aldehydes, principally 2-alkenals and 2, 4-dienals, in oils. The volatile compound analysis method measures secondary oxidation products formed during the decomposition of fatty acids. These comlb can be primarily responsible for the flavors in oils. The... 

Many methods have been developed to access the extent of oxidative deterioration, which are related to the measurement of the concentration of primary or secondary oxidation products or of both. The most commonly used are peroxide value (PV) that measures volumetrically the concentration of hydroperoxides, anisidine value (AV), spectrophotometric measurement in the UV region and gas chromatographic (GC) analysis for volatile compounds. Vibrational spectroscopy, because of its high content in molecular structure information, has also been considered to be useful for the fast measurement of lipid oxidation. In contrast to the time consuming chromatographic methods, modem techniques of IR and Raman spectrometry are rapid and do not require any sample preparation steps prior to analysis. These techniques have been used to monitor oil oxidation under moderate and accelerated conditions and the major band changes have been interpreted. ... 

Determination oe Secondary Oxidation Products ("Oee-Feavor" Voeatiees) 12.2.2.1 p-Anisidine Value Test... 

It can be seen from Equation (5.1) that the volume of steam required for deodorization is directly proportional to the system pressure and inversely proportional to the vapour pressure of the free fatty acid. Thus, a reduction in the former and an increase in the latter, brought about by increasing temperature, result in a reduction of time on temperature for a set steaming rate. This is correct for the simple reduction of fatty acid levels. However, oils vary in their content of pigments and oxidation products. Practical experience has shown that, whereas these products can be removed in the time required to reduce free fatty acid to the desired level from a good-quality feed oil, this is not so with oxidized oils. For such oils, an extended time at the selected temperature is required to allow thermal reactions to take place in which some of the oxidation products are further decomposed and the derivatives removed from the oil (Andersen, 1962 Brekke, 1980). If such oxidation products are not removed, the deodorized product will have a poorer taste and reduced oxidative stability. The limitations of this aspect of the deodorization process can be noted in the fact that to date the anisidine value, which is a measure of secondary oxidation products in the oil, is not reduced to zero. Commercial plants are currently designed for holding time on temperature of 30-120 min, but all are capable of extension. 

Anisidine Value measures the extent of oxidative deterioration, which spectrophoto-metrically estimates aldehydes, and secondary oxidation products. 

Other indices measure a secondary stage of oxidation, such as the anisidine value (ANV), pointing to formation of carbonyl compounds, capable of undergoing condensation reactions with p-anisidine, and the thiobarbituric acid reactive substance (TBARS) pointing to the presence of malondialdehyde (MDA) in particular. In biological systems, TBARS is of widespread use as a measure for the extent of oxidation damage. Another test for stability of oils to oxidation is based on the development of acidity as secondary product, for example, standards using the Rancimat equipment or a similar setup. 

---