Development and evaluation of a novel sensor for the in situ assessment of frying oil quality

Abstract

An objective appraisal of the quality of frying oil is important to ensure a wholesome fried product of adequate shelf-life at an economical cost. A novel frying oil monitor has therefore been developed suitable for simple, reliable, in situ oil quality determination. A literature study was carried out which showed that the viscosity at 20–100°C was correlated with the frying oil quality. Extrapolation to frying temperatures yielded the specifications for a prototype probe which was subsequently adapted from a novel GEC Marconi viscometer. The probe was then evaluated for three frying media with differing chemical characteristics. The assay of polymerized and oxidized matter (POM) content was employed as the reference method. The trial showed that the probe can monitor the viscosity of frying media at 170°C and that this viscosity is correlated with the quality of the oil. In contrast to colour and free fatty acid content, which were also measured, the probe output showed only a weak dependence on the oil type. It was possible to define a cut-off value for the probe output for which the calibration curves for the three oils in the trial fell between the two limiting values given for the POM content of an acceptable frying oil, namely 10 and 15%. The probe can be used in situ in hot frying oil and is suitable for adaptation both as an inexpensive dip probe and as a continuous in-line monitor.