Effect of cooking on residues of ormetoprim and sulfadimethoxine in the muscle of channel catfish

Abstract

Channel catfish Ictalurus punctatus were fed Romet medicated feed at doses of 25, 50, and 100 mg Romet per kg of fish daily for 5 d. To keep Romet concentration high enough for evaluation of cooking effects, fillets were sampled without the 3 d withdrawal period required by the US Food and Drug Administration. Concentrations of ormetoprim (OMP) and sulfadimethoxine (SDM), the antibiotics in Romet, were determined by a high-pressure liquid chromatography method in fillets before and after cooking. Fillets were cooked by one of four methods: smoked at 160–200 °C, baked at 190 °C, fried in canola oil at 190 °C, and injected with a mixture of 6% polyphosphate solution, frozen for 4 weeks, and then fried in vegetable oil at 190 °C. The average OMP concentrations in cooked tissue were 0.23, 0.66, and 1.22 μ/g dry basis (db) and SDM concentrations were 2.64, 2.73, and 3.74 μg/g db for fish dosed with Romet at levels of 25, 50, and 100 mg/kg, respectively. Cooking caused an average 54.0% reduction of OMP and 46.1% reduction of SDM from raw fillet of fish. Cooking significantly reduces both OMP and SDM residues in fillets and provides an additional margin of safety for consumers. Results for the four cooking methods were not statistically different.