Understanding microwave heating of oils

Our recent study found that vegetable oils, often considered as unsuitable for microwave heating, heat readily in microwave ovens. To explore chemical components within vegetable oil that contribute to microwave heating, we proposed two hypotheses: 1) water dissolved in oil and 2) glycerol component of oil molecule. In this research, we used the resonant cavity method to measure dielectric properties of vegetable oil with different water activities and compared vegetable oil with mineral oil (which does not contain the glycerol component). Our results showed no significant difference in the dielectric properties or microwave heating rates between vegetable oils with low (0.16) and high (1.00) water activities, indicating that dissolved water is not a major contributor. In contrast, vegetable oil heats well in microwaves, whereas mineral oil does not. The microwave heating difference was explained by the measured dielectric properties: the loss factor of vegetable oil (0.15) was 30 times greater than that of mineral oil (0.005). This supports our hypothesis that the glycerol component in vegetable oil contributes to microwave heating, whereas the absence of glycerol in mineral oil leads to the limited microwave heating capability. This research provides further fundamental understanding about microwave heating of oils.