Fermentation liquid stored at -80 °C was thawed at room temperature, mixed with methanol in a 1:1 ratio and refrigerated at -18 °C for 24 h to precipitate the proteins. After centrifugation (4 °C, 24,400 × g, 10 min), 50 μL of supernatant was mixed with 900 μL of solvent (50% methanol in water) and 50 μL of internal standard fluconazole at a final concentration of 0.1 µg mL -1 . Samples were measured immediately after preparation.