Nuclear Magnetic Resonance Spectroscopic Analysis of the Evolution of Peroxidation Products Arising from Culinary Oils Exposed to Thermal Oxidation: An Investigation Employing (1)H and (1)H-(1)H COSY and TOCSY Techniques

Scientific warnings on the deleterious health effects exerted by dietary lipid oxidation products (LOPs) present in thermally stressed culinary oils have, to date, not received adequate attention given that there has been an increase in the use and consumption of such oil products in everyday life. In this study, high-resolution (1)H nuclear magnetic resonance (NMR) analysis was used to characterize and map chemical modifications to fatty acid (FA) acyl groups and the evolution of LOPs in saturated fatty acid (SFA)-rich ghee, monounsaturated fatty acid (MUFA)-rich groundnut, extra virgin olive, and macadamia oils, along with polyunsaturated fatty acid (PUFA)-rich sesame, corn and walnut oils, which were all thermally stressed at 180 °C, continuously and discontinuously for 300 and 480 min, respectively. Results acquired revealed that PUFA-rich culinary oils were more susceptible to thermo-oxidative stress than the others tested, as expected. However, ghee and macadamia oil both generated only low levels of toxic LOPs, and these results demonstrated a striking similarity. Furthermore, at the 120 min thermo-oxidation time-point, the discontinuous thermo-oxidation episodes produced higher concentrations of aldehydic LOPs than those produced during continuous thermo-oxidation sessions for the same duration. On completion of the thermo-oxidation period, a higher level of triacylglycerol chain degradation, and hence, higher concentrations of aldehydes, were registered in culinary oils thermally stressed continuously over those found in discontinuous thermo-oxidized oils. These findings may be crucial in setting targets and developing scientific methods for the suppression of LOPs in thermo-oxidized oils.