THESIS
2016
106 pages : illustrations (some color) ; 30 cm
Abstract
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...[
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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.
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