Penicillin and tetracycline residues in selected fresh and UHT milk with different fat contents

The aim of the present work was to determine the residues of penicillin and tetracycline in selected fresh and UHT milk with different fat contents (< 2, 2, and > 2%). A total of 84 different milk samples (36 fresh and 48 UHT) purchased from retail chains in Silesia Region (Poland) were analysed. Penicillin and tetracycline residues were determined by the ELISA immunoenzymatic method. The obtained results were compared with MRL values adopted in Commission Regulation (EU) No. 37/2010. The results were additionally analysed statistically. Penicillin and tetracycline were found to be common in the analysed milk samples. Both antibiotics were present in low concentrations, and not exceeding their MRL. The median of penicillin residues was 0.298 µg/L, and 0.970 µg/L for tetracycline. For some samples, the determined levels of antibiotic residues did not exceed the limit of detection (LOD): three samples for penicillin (1.15%), and 24 samples for tetracycline (28.57%). A weak negative correlation between the level of penicillin and tetracycline residues was found (p = -0.218), where the decrease in penicillin concentration weakly correlated to the increase in tetracycline concentration. The level of residues of both antibiotics was significantly higher in fresh milk than in UHT milk (by 11.75% for penicillin, and 17.73% for tetracycline); for penicillin, Zcorrected = 2.445, and p = 0.0145, and for tetracycline, Zcorrected = 3.914, and p = 0.000091.