1.Conductivity method

Since the addition of seasonings such as salt in the cooking process of waste oil, the ionized substances produced by the decomposition of organic matter during the heating process, and the metal ions in the sewage make its conductivity increase , so the edible oil mixed with waste oil can be used. Measure its conductivity and compare it with qualified edible oil. Zhu Rui et al.  found that the electrical conductivity of cooking oil mixed with waste oil is much higher than that of qualified cooking oil sold in the market. The average conductivity of waste oil is about 10 times that of rapeseed oil and 10 times that of soybean salad oil. 11 times that of sesame oil. This method can quickly detect and identify adulterated oil, but it is only limited to waste oil or second (multiple) use oil.

2.Spectroscopy

At present, infrared spectroscopy, ultraviolet spectroscopy and Raman spectroscopy are commonly used in the identification of adulterated oils , and Raman spectroscopy is often used in combination with infrared spectroscopy. Spectroscopy has the advantages of simplicity, rapidity and low cost, but the spectrograms obtained by using spectroscopic methods for adulteration identification often need to be analyzed in combination with chemometric methods before conclusions can be drawn. Huang Xiuli et al[38] used Fourier transform infrared spectroscopy to detect olive oil mixed with palm oil, sunflower oil, peanut oil, corn oil, soybean oil, and rapeseed oil, and found that it can quickly and efficiently detect up to 5% adulterated olive oil.

3.Chromatography

High-performance liquid chromatography (HPLC) and gas chromatography are currently the most commonly used methods in the identification of adulterated oils. Since the composition and content of fatty acids in different vegetable oils are different, the change of fatty acids in the oil to be tested can be used to determine the oil to be tested. Test whether the oil is adulterated oil. determined the fatty acid composition , obtained the normal value of fatty acid composition ratio of common vegetable oils through screening and optimization, and established the common Vegetable oil GC adulteration detection technology, this technology can quickly determine the type of vegetable oil, and can qualitatively and quantitatively analyze adulterated vegetable oil.