Adulteration of cooking oil has become a serious public health concern in China. "Gutter oil" refers to used oil that is recycled from unhygienic waste oil, and by some estimate accounts for about 10% of the cooking oil market. This research aims to develop a simple and quick quality control method for edible cooking oils based on polar metabolite profiling and spectral fingerprinting using GC-MS. This method does not require time-consuming derivatization reactions and does not depend on any particular marker for authentication. Acetonitrile (ACN) is used to extract the polar components from cooking oil samples. This method removes most triglycerides which do not offer much discrimination and not amenable to GC-MS analysis. Normalized and baseline-corrected chromatograms were s...[ Read more ]

Adulteration of cooking oil has become a serious public health concern in China. "Gutter oil" refers to used oil that is recycled from unhygienic waste oil, and by some estimate accounts for about 10% of the cooking oil market. This research aims to develop a simple and quick quality control method for edible cooking oils based on polar metabolite profiling and spectral fingerprinting using GC-MS. This method does not require time-consuming derivatization reactions and does not depend on any particular marker for authentication. Acetonitrile (ACN) is used to extract the polar components from cooking oil samples. This method removes most triglycerides which do not offer much discrimination and not amenable to GC-MS analysis. Normalized and baseline-corrected chromatograms were subjected to chemometric analysis using principal component analysis (PCA). Five types of cooking oils: canola, corn, peanut, olive and lard oil were examined. It was found that the ACN extraction method was able to produce characteristic, easily distinguishable chromatographs for the 5 types of oils by PCA. To determine if used oils can be detected by this method, fresh oil samples were heated with or without food. The chromatographs showed visible changes over time, and a clear trajectory of data points was observed in the PCA plot as cooking time increases. Changes in volatile compounds, free fatty acids, tocopherols and sterols were observed as cooking time increases. A process was developed to mimic gutter oil production, which includes steps of neutralization by alkali, color and odor adsorption by activated clay. The reprocessed used oils were largely odor-free, had the right pH, and resembled fresh oils. However, the GC-MS chromatographic fingerprint of the recycled used oil can be clearly distinguished from that of the original fresh oils by PCA, showing the potential of this method in the quality control of cooking oils.