The effect of boiling on stability of oxytetracycline and sulfamethazine residues in raw milk using HPLC method

Abstract

Two hundred raw milk samples (250 ml of each) were collected from small dairy farms, street peddlers and dairy shops in Mansoura Governorate. These samples were screened using Bacillus Subtilis Diffusion Assay for qualitative detection of antibiotics residues; where the percentage of suspected positive samples was 12.5%. High Performance Liquid Chromatography – Ultra Violet detector (HPLC- UV) method was developed and validated to determine the amount of oxytetracycline (OTC) and sulfamethazine (SMZ) residues in raw milk before and after boiling. The results revealed that 8.5 % of the raw milk samples were containing (OTC) residues (6.5 % of them exceed MRL) while, (SMZ) was detected in4 % of the raw milk samples (3 % of them exceed MRL). Upon applying heat treatment, the reduction in the (OTC) content in milk boiled for 2 minutes was 30.5% but boiling for 5 minutes was accompanied with 54.1% reduction. On the other hand, the percentage of (SMZ) reduction was 1.7% and 9.5% in milk boiled for 2 and 5minutes respectively which could be attributed to the low heat stability of (OTC) and high stability of (SMZ).