Heat Treatment Effects on the Antimicrobial Activity of Macrolide and Lincosamide Antibiotics in Milk

Antibiotic residues in milk can cause serious problems for consumers and the dairy industry. Heat treatment of milk may diminish the antimicrobial activity of these antibiotic residues. This study analyzed the effect of milk processing (60 degrees C for 30 min, 120 degrees C for 20 min, and 140 degrees C for 10 s) on the antimicrobial activity of milk samples fortified with three concentrations of three macrolides (erythromycin: 20, 40 and 80 mu g/liter; spiramycin: 100, 200, and 400 mu g/liter; and tylosin: 500, 1,000, and 2,000 mu g/liter) and one lincosamide (lincomycin: 1,000, 2,000, and 4,000 mu g/liter). To measure the loss of antimicrobial activity, a bioassay based on the growth inhibition of Micrococcus luteus was done. The data were analyzed using a multiple linear regression model. The results indicate that treatment at 120 degrees C for 20 min produces inactivation percentages of 93% (erythromycin), 64% (spiramycin), 51% (tylosin), and 5% (lincomycin), while treatment at 140 degrees C for 10 s results in generally lower percentages (30% erythromycin, 35% spiramycin, 12% tylosin, and 5% lincomycin). The lowest loss or lowest reduction of antimicrobial activity (21% erythromycin and 13% spiramycin) was obtained by treatment at 60 degrees C for 30 min.