Mr. Zhen Yan Li
Deep-frying is a popularly used cooking method, and deterioration of oil during deep-frying has been a public concern. However, the transfer and accumulation of heavy metal contents from deep-fried food to oil have not been well studied. This study aims to address this by a series of deep-frying experiments using rapeseed oil, a common deep-frying oil, to repeatedly deep-fry oyster, a common frying food with high metallic content. The oil was sampled at different deep-frying cycles, and the samples were digested and analysed using inductively coupled plasma mass spectrometry. The results showed that the arsenic content in oil could be accumulated to over 0.1 ppm, a limit as established by the Hong Kong government, after 16 deep-frying cycles, and could reach as high as over 0.5 ppm with more frying cycles. The arsenic concentrations in the strained residues were found to be over 100 times higher than that of the deep-frying oil. Further investigation indicated that the residue particles with the accumulated arsenic were formed from liquid leached from the oyster during the deep-frying. This study revealed that arsenic can be accumulated to alarming levels during the deep-frying of oyster, which can cause food safety concerns and potential legal issues. Future studies on the speciation of arsenic and evaluation of relevant food safety issues are ongoing.