Oxidation kinetic studies of oils derived from unmodified and genetically modified vegetables using pressurized differential scanning calorimetry andnuclear magnetic resonance spectroscopy

Evaluation of oxidative stability of a series of vegetable oils and oils de rived from genetically modified vegetables were carried out using pressure differential scanning calorimetry (PDSC). The purpose of including the gene tically modified oils along with other oils were to illustrate the effect o f high oleic and linoleic content on the thermal and oxidative behavior of these oils. Kinetic and thermodynamic parameters were computed and variatio n of results explained in terms of structural data derived from quantitativ e H-1 and C-13 NMR spectroscopy. For a variety of vegetable oil samples use d in the study, log b (program rate of heating; i.e. 1, 5, 10, 15 and 20 de greesC/min) was linearly related (R-2 = 0.99) to the reciprocal of absolute temperature corresponding to maximum oxidation rate (peak height temperatu re). From the resulting slope it was possible to compute activation energy (E-a) for oxidation reaction and various other kinetic parameters, e.g. rat e constant (k), Arrhenius frequency factor (Z) and half-life period (t(1/2) ). The presence of C-C unsaturation in the fatty acid (FA) chain, their nat ure and relative abundance, affect thermal and oxidative stability of the o il and subsequently their kinetic and thermodynamic parameters. Quantitativ e analysis of the NMR spectra yielded various other structural parameters t hat were correlated with start (Ts) and onset (To) temperature of vegetable oil oxidation, and certain important kinetic parameters (E-a and k). This is a novel approach, where statistical models were developed as a predictiv e tool for quick assessment of oxidative and thermodynamic data. The correl ations developed have an adjusted R-2 of 0.922 and higher using 3 or 4 NMR derived predictor variables. These correlations revealed that in addition t o nature and abundance of C=C, relative abundance of other structural param eters (e.g. bis-allylic methylene group, allylic-CH2, alpha -CH2 to C=O, et c.) influence oxidation and kinetic data. Published by Elsevier Science B.V .