Destruction of penicillin residues in waste milk

Abstract

To destroy the antibiotic residuals in waste milk on dairy farms, the aim of this study was to develop an approach for the degradation of Penicillin G in waste milk on the farm, working efficiently and without posing a risk to the user or the environment. Bovine pasteurized and homogenized milk with 3.8 % of milk fat was spiked with Penicillin G sodium-salt to an initial concentration of Penicillin G in the milk of 4 µg/kg to 500 mg/kg. Degradation of Penicillin G was performed by physico-chemical treatments, namely 1) exposure to heat and 2) exposure to heat after prior acidification and by 3) enzymatic degradation by β-lactamases from Escherichia (E.) coli strains tested positive for extended spectrum β-lactamases (ESBL) production. Heating to 95 °C for 120 minutes led to a degradation of 4 µg/kg Penicillin G below the detection limit of 2 µg/kg. A higher Penicillin G concentration of 8 µg/kg could not be sufficiently degraded anymore.  Heat treatment for 120 minutes at pH 5.0 resulted in a degradation of 500 µg/kg, whereas it was 64 µg/kg pH 5.5. In conclusion, it is technically possible to degrade Penicillin G in waste milk. A combination of acidification of the milk and heating lead to a degradation of very high antibiotic concentrations but assumes a high level of technical equipment, time, and energy supply. The enzymatic degradation process of the antibiotic by β-lactamases promises better results than heating and acidification and requires lower temperatures than the methods without enzymatic degradation. A possible transmission of plasmids from the enzyme solution must be considered and needs to be solved.