Effect of freezing on stability of oxytetracycline residues in beef from Dodoma region, Tanzania
The aim of this study was to determine the effect of freezing on the concentration of oxytetracycline (OTC) residues in beef samples stored at -20 °C (core beef temperature -12 °C and below) for 60 and 120 days. A total of 60 fresh beef samples were randomly obtained from cattle slaughterhouses and butcher shops in districts in Dodoma region in Tanzania. The OTC residues were determined using high performance liquid chromatography (HPLC) with a diode array detector (DAD). Results showed that the mean concentration of OTC residues in 16 positive samples before freezing was 191.71 ± 90.21 ng/g. The mean concentration of OTC after freezing at -20 ºC for 60 and 120 days were 166.40 ± 86.49 ng/g and 133.50 ± 83.24 ng/g respectively. These results revealed a significant (p<0.05) reduction of OTC residues of 30% after 60 days and 65% after 120 days of freezing at -20 °C. The percentage reduction of OTC residues was not dependent on the initial concentration or the freezing process but was rather due to unknown time dependent individual beef sample factors. It is concluded that, despite OTC levels in beef decreasing due to non-freezing factors, any residues significantly above Maximum Residues Level (MRL) may not be expected to reduce to acceptable levels as a result of freezing .
Key words: Oxytetracycline, cold storage, HPLC, beef.