This work presents a novel apparatus and method for determining frying oil quality based on the measurement of the rate of spontaneous capillary penetration in porous media. The rate of liquid penetration of a wetting liquid in a porous medium having pores of capillary dimensions depends on the liquid and porous medium properties (liquid viscosity and surface tension, liquid/solid contact angle, pore sizes and tortuosity of the porous medium). Furthermore, and depending on penetration conditions, the penetration rate can be affected also by gravity, inertia, spreading pressure and other variables. The measurement of capillary penetration rate has been used in the past for the determination of contact angles and/or pore radii in porous media. To our knowledge, the present method is the first effort to use the measurement of capillary penetration rate for the determination of liquid properties and particularly frying oil quality. Frying in the food industry/catering sector involves heating the oil for several days in the presence of food. This process results in serious quality degradation with negative effects for human health. The major groups of compounds formed during frying are polar and polymer compounds which change the oil’s surface tension and viscosity.A rapid test is being developed measuring frying oil quality taking advantage of the changes in frying oil properties and based on the measurement of capillary penetration rate. A prototype design and results on model liquids and oils heated/fried under different conditions are presented proving the capabilities of the method.
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