The formation of cholesterol oxidation products (COPs) during heating of cholesterol at 150 °C for
up to 30 min was kinetically studied using nonlinear regression models. The various COPs were
analyzed by TLC and HPLC. Results showed that the COPs concentration increased with increasing
heating time, and the cholesterol loss reached 64.8% after 30 min of heating. In the early stage of
oxidation, the highest rate constant (h-1) was observed for 7-hydroperoxycholesterol (7-OOH)
formation, followed by epoxidation, dehydration, reduction, and dehydrogenation. The reactions
for formation of 7-OOH (7α-OOH and 7β-OOH) and 5,6-epoxycholesterol (5,6α-EP and 5,6β-EP) fit
the second-order, while the other reactions fit the first-order. The correlation coefficients (r
2) for
the reactions ranged from 0.79 to 0.99. The kinetic model developed in this study can be used to
predict the concentration changes of COPs during the heating of cholesterol.
Keywords: Cholesterol oxidation; heating; kinetic model; HPLC analysis
The objectives of this study were to develop a gas chromatography-mass spectrometry (GC-MS) method to analyze the contents of cholesterol oxidation products (COPs) in marinated eggs, pork, and juice and to compare the effect of heating time and soy sauce or sugar on the formation of COPs. By using a silica cartridge for purification and GC-MS with selected ion monitoring for detection, seven COPs, including 7alpha-hydroxycholesterol, 7beta-hydroxycholesterol, 5,6alpha-epoxycholesterol, 5,6beta-epoxycholesterol, 5alpha-cholestane-3beta, 5,6beta-triol, 5-cholesten-3beta-25-diol, and 7-ketocholesterol, as well as internal standard 5alpha-cholestane, were resolved within 16 min by using a HP-5MS capillary column. During marinating, the levels of most COPs followed an increasing trend with increasing heating time. However, a higher amount of COPs was generated for ground pork as compared to eggs. The incorporation of soy sauce or sugar (1 and 10%) was effective in inhibiting COPs formation, with the latter being more pronounced than the former in both marinated eggs and pork.
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