Abstract: To develop a rapid and reliable method for the identification of waste cooking oil (WCO), this study investigated the effects of heat treatments during oil processing, use and repetitive refining on the ultraviolet (UV) spectrum of rapeseed oil. UV spectra of oil samples were collected using a thin film chamber with an optical lenghth of 0.05 mm and two characteristic parameters from the UV spectra, i.e. D245 nm and R272 nm, were selected to evaluate the contents of di- and tri-conjugates. The results showed that the maximum values of D245 nm and R272 nm for refined rapeseed oil (RO) were no more than 4.8 and 12.9, respectively. High-temperature oxidation could lead to a significant increase in both D245 nm and R272 nm, while repetitive refining of oxidized RO could not decrease R272 nm. Therefore, a branch discrimination process based on D245 nm and R272 nm could be used for discrimination of oxidized or repeatedly refined oil from normal RO. The detectable threshold of deodorized WCO adulterized in normal RO was 2.3%.

Key words: refined waste rapeseed oil, ultraviolet spectrum, characteristic parameters, identification indicators, branch discrimination