Microwave heating of different vegetable oils: relation between chemical and thermal parameters

Changes of DSC profiles and thermal properties (upon cooling and heating) were evaluated at different times of microwave heating on refined peanut (Pto), high oleic sunflower (HOSo) and canola (Co) oils and compared to the results obtained for standard chemical indices (free fatty acids, peroxide, p-anisidine, OSI time) and antioxidant activity (Trolox equivalent antioxidant capacity values). Co was more extensively oxidised by microwave heating than the other two oils probably as a consequence of the higher degree of unsaturation, even though it showed a higher antioxidant activity. Microwave heating also induced alterations in both cooling and heating profiles of the oils, mainly in Pto and Co, shifting phase transitions towards lower temperature and enlarging temperature range. High statistical correlation coefficients were obtained among thermal properties both upon cooling and heating and chemical indices (i.e. free fatty acids and p-anisidine values). The analysis of both cooling and heating profiles and related thermal properties appears to be a very useful tool to assess different degrees of lipid thermoxidation induced by microwave in vegetable oils, which could be useful for the ready-to-eat food sector and the vegetable oil industry.