Effect of drug residues on rennet coagulation of milk

The aim of this study was to consider the problem of residual drugs in cow’s milk and to define the influence of such residues in the milk coagulation process, including the case in which the concentration is below the lowest limits permitted by law. Compounds that have EU maximum residue levels (MRLs) were selected. Through milk dynamographic analysis, the chemical and rheological parameters (r, k20 and a30) were determined in relation to the different quantities of drug additions. Effects on coagulation were demonstrated for high concentration. The only residue that demonstrated significant effects at MRL value was trimethoprim. These results were confirmed using electron microscopy, rheological studies and near-infrared spectral analysis.