Understanding microwave heating of oils

Abstract

Our recent study found that vegetable oils, often deemed unsuitable for microwave heating, actually heat efficiently in microwave ovens. To explore the main chemical components within vegetable oil that contribute to microwave heating, we considered two hypotheses: 1) the presence of water dissolved in oil and 2) the 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 revealed 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. Regardless of the water activity levels, vegetable oil heats well in microwaves, whereas mineral oil does not. The microwave heating difference was elucidated 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 its absence in mineral oil accounts for the limited microwave heating capability. This research augments our fundamental comprehension of microwave heating of oils.