Comparison of Sensing Methods for Characterization of Heated Oils Degradation

The oil quality after the long heating time is required to be examined frequently because the degradation of oils can be detrimental to human health. Several sensing methods have addressed oil degradation problems but currently there is no known techniques to solve the problem in both efficient and economical ways. Three sensing methods, i.e. an interdigital planar sensor integrated with a LCR meter, spectrophotometer method and tested sensing paper, are proposed to characterize the quality of two kinds of edible oils. It is found that the logarithm of impedance of oils is linearly related to the logarithm of measured frequency, implying that the oils are dielectric materials. The impedances of oils decrease linearly with the increase of heated duration and the capacitance ratio of oils is weakly dependent on the heating duration. The wavelengths of starting transmittance are significantly red-shifted as observed by a spectrophotometer when the oils are heated for a long time. The absorbance of the oils increases exponentially with the heating time. The tested paper indicates that the color change can exhibit a quick oil qualitative measurement within a few minutes, but lacks quantitative information. Each sensing method has different sampling time, precision and accuracy for measuring the oil degradation, and the sensing methods should be chosen according to the required needs.