A trace analysis of oxytetracycline and tetracycline residues in pasteurized milk supplied in Tehran: a one-year study (April 2011-March 2012)

Tetracyclines (TCs) are broad-spectrum antibiotics that are widely used in veterinary medicine. The presence of TCs residues in milk is a public health concern all over the world. This study aimed to determine TCs residuals in pasteurized milk marketed by some dairy companies in Tehran from April 2011 to March 2012. 432 pasteurized milk samples were purchased from supermarkets supplying the milk products of 12 major dairy companies in Tehran (3 samples from each company every month), and they were stored at -20 0C until analysis. Oxytetracycline (OTC) and Tetracycline (TC) residues in each sample were extracted by a liquid - liquid phase procedure and quantitated using a high performance liquid chromatographic (HPLC) method. Chromatographic conditions included a mobile phase as oxalic acid buffer- acetonitril (80: 20) with a flow rate of 1mL/min and UVdetection at 355 nm. TCs residuals in most milk samples were lower than 100 ppb, maximum residue level (MRL); however, in seven samples (1.62%) the total residues of OTC and TC were more than MRL. In the latter milk samples, the median total TCs residue was 625 ppb, ranging between 274 and 1270 ppb. Because of the presence of TC residues above the MRL level in a limited number of milk samples, it is concluded that more studies and supervision of health authorities are needed in this field.