2.3.1. ELISA screening analysis
Aliquots of 1.3 g of raw milk were weighted into glass tubes and centrifuged at 1700 × g for 5 min. Aliquots of 100 μL of the supernatant were placed into individual wells of the microplate kit for the immunoassay test. After a wash step, samples were stirred for 30 s and incubated in the dark at room temperature (25 °C) for 30 min. No washing step was performed prior to the addition of the enzyme conjugate. After incubation, 100 μL of the enzyme conjugate were added to each well and gently shaken for 30 s. Samples were incubated again for 15 min under the same conditions. Subsequently, four washing steps were carried out on an automated plate washer, followed by the addition of 100 mL of substrate to each well and another incubation as previously described. Finally, 100 mL of the stop solution were added to each well and absorbances readings were performed.