Abstract
Regenerated gutter oil (i.e., waste oil) accounts for 10% of the edible oil market, which has caused serious food safety issues. Currently, there is no standard protocol for the identification of the gutter oil. In this study, the pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) method was employed to analyze eleven oil samples including edible vegetable oils (tea oil, corn oil, olive oil, sunflower oil, peanut oil and blend vegetable oil) and waste oils (used frying oil, lard, chicken fat, inferior oil and kitchen waste grease). Three factors of pyrolysis temperature, reaction time and sample volume were investigated to optimize the analytical parameters. The optimal pyrolysis conditions were determined to be 600°C, 1 min and an injection volume of 0.3 μL. Five characteristic components (tetradecane, z,z-9,12-octadecadienoic acid, decanoic acid-2-propenyl ester, 17-octadecenoic acid, and z-9-octadecenoic acid) were found in all oil samples. The existence of C11-C16 olefins in the pyrolytic products of the animal fats and the other low-quality oils could be utilized to distinguish vegetable oils from gutter oils.
Highlights
In the past ten years, food safety issues related to the reuse of waste oil or grease have been frequently exposed [1]
The pyrolysis temperature refers to the temperature whose sample is pyrolyzed in the pyrolysis furnace, i.e., the temperature before entering the gas chromatography (GC)
The direct pyrolysis of the waste oils without methyl esterification was performed by Py-gas chromatography coupled with mass spectrometry (GC/MS) and the parameters were optimized
Summary
In the past ten years, food safety issues related to the reuse of waste oil or grease (i.e., gutter oil) have been frequently exposed [1]. It is estimated that the regenerated waste oil accounts for up to 10% of the cooking oil market, i.e., about 2.5 to 3 million tons of waste oil returns to the dining table every year [2]. In addition to the conventional physical and chemical indicators, the current detection/analytical methods of waste oils include various chromatographic methods, spectroscopy, nuclear magnetic resonance, etc. Due to the complicated sources of waste oil, the complex composition, different processing methods, and different refining degrees, there is no single specific indicator or standard to distinct waste oils from edible oils. It is imperative to develop a standard analytical method for the detection of the waste oil
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