Effect of processing on the degradation of tetracyclines in milk and milk products (original) (raw)

Tetracyclines are considered an important group of broad spectrum antimicrobials employed in Brazil in several species of animals producing food, including bovine, swine and fish. A HPLC method for the determination of oxytetracycline (OTC), doxycycline (DC) and tetracycline (TC) residues in milk and yogurt was developed and validated. The method was used to evaluate the degradation of these antimicrobial contaminants during the thermal treatment of milk, as well as during yogurt preparation and storage. Sample extraction was carried out using 30% (v/v) trichloroacetic acid to precipitate the proteins. For the HPLC analyses a Varian C 8 analytical column (250× 4.6 mm, 5 m) with a mobile phase: sodium acetate 0.1 mol L −1 + EDTA 25 mmol L −1 + calcium chloride 35 mmol L −1 : methanol (65:35, v/v) and fluorescence detection (λ excitation: 420 nm and λ emission: 530 nm) was used. Tetracycline recovery in milk and yogurt was 92-98% (OTC); 87-83% (DC) and 89-97% (TC). The quantitation limit was 27, 46 and 33 ng mL −1 for OTC, DC and TC, respectively. Different thermal treatments were used to evaluate the heat stability of the tetracyclines in milk: cooking stove treatment, hot plate and microwave oven. Higher degradation occurred using the hot plate, 10.9% (OTC), 27.7% (DC) and 15.0% (TC). With respect to the stability of the tetracyclines during the preparation and shelf life of yogurt, it was verified that 500 ng mL −1 (OTC), 1120 ng mL −1 (DC) and 600 ng mL −1 (TC) did not inhibit yogurt production, and that after 30 days under refrigeration (4 • C), residual levels of the contaminants still remained in the samples. Nonetheless, in relation to the original contamination in the yogurt, the tetracycline levels had diminished by 52%, 61% and 67%, for OTC, DC and TC, respectively. The data indicated that when conducting a risk assessment of tetracyclines in human health, the presence of these contaminants in milk and yogurt should be considered as a potential source. In addition, in order to protect consumer health, the governmental agencies should monitor the application of good practices in the use of these antimicrobials in the treatment of cows that produce milk for human consumption, as well as conducting health surveillance actions in order to control the residue levels of these substances in commercialized milk and yogurt.