THE EFFECT OF COOKING ON VETERINARY DRUG RESIDUES IN FOOD .4. OXYTETRACYCLINE

The heat stability of oxytetracycline (OTC) in water and vegatable oil was investigated. Results showed that the drug was unstable in water at 100 degrees C with a half-life of about 2 min, but more stable in o il at 180 degrees C where the half-life was about 8 min. The effect of a range of cooking processes including microwaving, boiling, roasting , grilling, braising and frying on OTC residues in incurred animal tis sues was investigated. Substantial net reductions in OTC of 35-94 % we re observed, with temperature during cooking having the largest impact on the loss. Migration from the tissue into the surrounding liquid or meat juices was observed during the cooking processes. Diode-array an alysis of heat-treated OTC standard solutions indicated that no indivi dual closely related compound such as 4-epioxytetracycline, alpha- or beta-apooxytetracycline formed a significant proportion of the breakdo wn products. OTC was not evenly distributed throughout the tissue, but the effects of this were minimized by selecting adjacent samples for cooking and for the raw control. The findings of this investigation sh owed that the effect of cooking on residues of OTC should be considere d before data obtained from measurements on raw tissue are used for co nsumer exposure estimates and dietary intake calculations.