THE EFFECT OF COOKING ON VETERINARY DRUG RESIDUES IN FOOD .3. SULFAMETHAZINE (SULFADIMIDINE)

The heat stability of sulphamethazine was investigated. The drug was s hown to be stable in boiling water at 100 degrees C. In cooking oil at 260 degrees C, losses were observed, indicating a half-life of about 5 min. At 180 degrees C in cooking oil, sulphamethazine was unstable w ith a half-life of about 2 h. The effect of a range of cooking process es (boiling, roasting, grilling, frying, pressure cooking and microwav ing) on sulphamethazine residues in incurred animal tissue was studied . Once allowance for weight loss during cooking had been made no net u naccountable change in concentration of sulphamethazine was observed i n any of the cooking processes investigated. During frozen storage, su lphamethazine residues were found to be stable over a period of 3 mont hs. It was found during this investigation that the method used for an alysis which involved acid extraction converted the N-4-metabolites to parent sulphamethazine, and hence only sulphamethazine was measured. Sulphamethazine was found to be evenly distributed in the raw incurred tissue used for analysis. Migration from the tissue into the surround ing liquid or meat juices was observed during the cooking process. The findings of this investigation show that surveillance data obtained f rom measurements on raw tissue are applicable for use in consumer expo sure and dietary intake calculations, but only if an acidic extraction method which converts the N-4-metabolites to parent sulphamethazine i s used for the surveillance. This may not however conform to current M aximum Residue Limit legislation which refers to total parent sulphona mides. Different methods of analysis for sulphonamides are likely to g ive rise to inter-laboratory variation.