METHODS FOR MEASURING LIPID
OXIDATION
Numerous analytical methods are routinely used for
measuring lipid oxidation in foods. However, there is no uniform and standard
method for detecting all oxidative changes in all food systems. Therefore, it
is necessary to select a proper and adequate method for a particular
application. The available methods to monitor lipid oxidation in foods can be
classified into five groups based on what they measure: the absorption of
oxygen, the loss of initial substrates, the formation of free radicals, and the
formation of primary and secondary oxidation products. A number of physical and
chemical tests, including instrumental analyses, have been employed in
laboratories and the industry for measurement of various lipid oxidation
parameters. These include the weight-gain and headspace oxygen uptake method
for oxygen absorption; chromatographic analysis for changes in reactants; iodometric
titration, ferric ion complexes, and Fourier transform infrared (FTIR) method
for peroxide value; spectrometry for conjugated dienes and trienes,
2-thiobarbituric acid (TBA) value, p-anisidine value (p-AnV), and carbonyl
value; Rancimat and Oxidative Stability Instrument (OSI) method for oil
stability index; and electron spin resonance (ESR) spectrometric assay for
free-radical type and concentration. Other techniques based on different
principles, such as differential scanning calorimetry (DSC) and nuclear
magnetic resonance (NMR), have also been used for measuring lipid oxidation. In
addition, sensory tests provide subjective or objective evaluation of oxidative
deterioration, depending on certain details.
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