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

BACKGROUND: Tetracyclines (TCs) are broad-spectrumantibiotics that are widely used in veterinary medicine. Thepresence of TCs residues in milk is a public health concern allover the world. OBJECTIVES:This study aimed to determine TCsresiduals in pasteurized milk marketed by some dairy companiesin Tehran from April 2011 to March 2012. METHODS: 432pasteurized milk samples were purchased from supermarketssupplying the milk products of 12 major dairy companies inTehran (3 samples from each company every month), and theywere stored at -20 0C until analysis. Oxytetracycline (OTC) andTetracycline (TC) residues in each sample were extracted by aliquid - liquid phase procedure and quantitated using a highperformance liquid chromatographic (HPLC) method. Chromatographicconditions included a mobile phase as oxalic acidbuffer- acetonitril (80: 20) with a flow rate of 1mL/min and UVdetectionat 355 nm. RESULTS: TCs residuals in most milksamples were lower than 100 ppb, maximum residue level(MRL); however, in seven samples (1.62%) the total residues ofOTC and TC were more than MRL. In the latter milk samples, themedian total TCs residue was 625 ppb, ranging between 274 and1270 ppb. CONCLUSIONS: Because of the presence of TCresidues above the MRL level in a limited number of milksamples, it is concluded that more studies and supervision ofhealth authorities are needed in this field.