Fate of monensin during the making process of Minas Frescal cheese

Monensin is a polyether ionophore antibiotic widely used in animal feeding to prevent and treat coccidiosis, as growth promoter in ruminants and swines and to increase milk production in lactating cows. Therefore, residues of this drug may be found in food derived from animals, such as milk, which can be used to produce dairy products. Considering the lipophilicity of monensin and the possibility of its concentration in the curd, this work aimed to evaluate the fate of this substance during the making process of Minas Frescal cheese. For that, samples of raw milk were fortified with monensin at three different nominal concentrations (M1 = 1 ng mL−1, M2 = 2 ng mL−1, and M3 = 8 ng mL−1) and then pasteurized at 68 °C for 2 minutes, cooled and stored in a cold chamber (5 ± 1 ºC) until the cheese production. A sample of non-fortified milk was used as control (C). Monensin residues were evaluated using HPLC–MS/MS validated methods in the following steps: (a) raw milk; (b) pasteurized milk; (c) whey; and (d) cheese. Mean monensin concentrations (ng mL−1) for (a) were 1.2 (M1), 2.03 (M2) and 6.8 (M3) while for (b) the levels were 1.00 (M1), 1.76 (M2) and 6.63 (M3), showing a slight degradation due to pasteurization. For (d), monensin amounts (ng g−1) were 4.26 (M1), 9.31 (M2) and 32.14 (M3), showing a concentration in the cheese of about 5-fold. For whey (c), mean values (ng mL−1) were 0.31 (M1), 0.63 (M2) and 1.8 (M3), suggesting that a small amount of monensin is lost during draining. To our knowledge, this is the first work described in the literature that investigated the fate of monensin during the making process of milk-derived products and should alert the sanitary authorities about the need to monitor this drug in cheeses.