Effect of various heat treatments and cold storage on sulphamethazine residues stability in incurred piglet muscle and cow milk samples

The stability of sulphamethazine (SMZ) residues in incurred piglets muscle tissue and incurred cow milk, under various heat treatments (pasteurizing, boiling, autoclaving and microwaving) was studied. Moreover, the storage stability of SMZ residues at −20 and −75 °C as well as the stability of SMZ standard solutions under boiling and autoclaving conditions was also investigated. The results showed that in the pasteurized milk samples SMZ residues concentration remained unchanged, while in the boiled and autoclaved milk samples, a decrease in their concentration was observed. Regarding the heating treatments of piglet muscle, after allowance for weight loss and migration of SMZ into the surrounding fluid has been made, a considerable reduction in the quantity of SMZ in piglet muscle during boiling, autoclaving and microwaving, was confirmed. The decrease was higher in the autoclaved milk and muscle tissue samples than in the boiled ones, while the microwaved muscle tissue samples showed the lowest decrease. Since SMZ standard solutions were stable under boiling and autoclaving conditions, the decrease of SMZ measured concentrations in muscle and milk samples might be attributed to the binding of SMZ with proteins, which was caused by the various heat treatments. SMZ residues were stable at −20 and −75 °C in all samples examined for at least 3 and 5 months, respectively.