Transfer of antibiotics from goat's milk to rennet curd and whey fractions during cheese-making

The transfer of 35 antibiotics from milk to curd and whey was evaluated. Cheeses were produced at laboratory scale, from antibiotic-free goat's milk spiked with different antibiotic concentrations between 0.25 and 4 times the Maximum Residue Limits established in milk. Drug concentrations in milk, curd and whey were analysed by UHPLC-HRMS. Results indicated that most antibiotics were mainly transferred from milk to whey (up to 85.9%), with retention percentages in the curd lower than 50%, except for ceftiofur (59.7%) and dicloxacillin (52.8%). In most cases, drug distribution was unaffected by the antibiotic concentration in milk and correlated significantly to the drug lipophilicity (Log P) for beta-lactams (R-2 = 0.54) and sulfonamides (R-2 = 0.62). When drug ionization was considered (Log D), improved correlation coefficients were obtained for macrolides (R-2 = 0.98). However, other factors besides the drug solubility should be considered to explain and predict the partitioning of antibiotics during cheese-making.