Accumulation of arsenic and other potentially toxic elements in oil when deep-frying oyster and grouper fish fillets

Deep-frying is widely used, but with very few reports on transfer and accumulation of potentially toxic elements from deep-fried food to deep-frying oil. In this study, by deep-frying oyster with rapeseed oil, an experiment simulating the common industrial practice, we revealed that arsenic could be accumulated to 567±133 μg/kg in the oil, more than five times the maximum limit recommended by the Codex Alimentarius. Similar arsenic accumulation could also be observed when deep-frying grouper fish fillets or by using soybean oil, while the control experiment with chicken wings did not lead to detectable arsenic accumulation. Further investigation revealed that the arsenic accumulation was mainly caused by liquid leached from the food, which formed residues in the oil. Higher levels of potentially toxic elements in these residues indicated that accumulation of other toxic elements was possible if their concentrations in food were sufficiently high. The accumulation could be mitigated by battering the food and removing residues from the oil, leading to a reduction of approximately 75%, with arsenic levels decreased to 134±44 μg/kg. These results indicated the possible accumulation of toxic elements in repeatedly used cooking media, and suggested the potential need of monitoring toxic element contents for such media. • Deep-frying of oysters and grouper fish fillets was investigated. • Arsenic was accumulated to over 5 times the limit for the deep-frying oil. • Dehydration of leached liquid from food led to enrichment of arsenic in residues. • Arsenic accumulation could be alleviated by using batter to coat the food fried.