Review of rapid tests available for measuring the quality changes in frying oils and comparison with standard methods

Repeated use of oils and fats for frying of food brings about many changes in their physical and chemical properties. Due to increasing health concerns, the assessment of the quality of reused oils has received much attention, since such assessment is useful in determining the discarding point of the oils. The official analytical methods used in laboratories for this purpose need skill, time, and a large consumption of solvents. To make the oil testing simpler, several rapid test kits have been developed based on either physical parameters (such as viscosity or dielectric changes) or chemical parameters (such as free fatty acids, oxidized fatty acids, or carbonyl compounds). These test kits usually comprise a portable instrument or colorimetric reaction sticks, capable of providing a direct or indirect measurement of a single parameter. The review presented in this paper evaluates the use of such rapid test kits and highlights the need to develop multi-parameter test kits in order to establish the quality of reused oil and the point at which it should be discarded. The review also encompasses pertinent details on the standard analytical methods, and deterioration of frying oils that occur during and after their use and the associated health consequences.