## 2 Materials and Methods
### LC-MS/MS Analysis of Mycotoxins
Certified liquid standards of single and multiple mycotoxins (manufacturer: Romer Labs Diagnostic, Tulin, Austria) were used to prepare a stock standard mixture of 14 mycotoxins in acetonitrile, containing following concentrations: 0.025 \(\upmu\)g mL\({}^{-1}\) of aflatoxin B2 (AFLB2) and aflatoxin G2 (AFLG2), 0.1 \(\upmu\)g mL\({}^{-1}\) of aflatoxin B1 (AFLB1) and aflatoxin G1 (AFLG1), 0.5 \(\upmu\)g mL\({}^{-1}\) of ochratoxin A (OTA), 5.0 \(\upmu\)g mL\({}^{-1}\) of t'omnisin B1 (FB1), f'omnisin B2 (FB2), T-2 toxin (T-2), HT-2 toxin (HT-2) and zeaeralenone (ZEA), 20 \(\upmu\)g mL\({}^{-1}\) of deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON) and nivelenol (NIV). Working solutions were made by 5-, 10-, 50-, 100-, 500-, 1000- and 5000-fold dilution of the stock mixture with acetonitrile. The isotopically labeled standard solution of 13C17-ALFB1 at the concentration of 0.01 \(\upmu\)g mL\({}^{-1}\) prepared in acetonitrile by 50 times dilution of 1 mL of 0.5 \(\upmu\)g mL\({}^{-1}\) stock solution was used as internal standard (ILS). The stock and working mycotoxin standard mixtures were used to determine the calibration curves, recoveries and the limit of detections (LOD). All standard solutions and mixtures were kept in a freezer at \(-\)20 \({}^{\circ}\)C.  
Calibration mixtures of seven concentration levels were prepared by pipetting the following into 2-mL chromatography vials: 100 \(\upmu\)L of each standard mixture, 850 \(\upmu\)L of LC mobile phase (95% A and 5% B) and 50 \(\upmu\)L of internal standard (ILS). Internal standard 13C17-AB1 (ILS) was added to the final acetonitrile extracts just prior to determination step, in order to control the accurate injection of calibration standards and sample extracts into the LC-MS/MS system. The solution concentrations were as follows: for AFLB1 and AFLG1, in the range of 0.002-2 ng mL\({}^{-1}\) (corresponding to 0.04-40 ug kg\({}^{-1}\)); for AFLB2 and AFLG2, in the range of 0.0005-0.5 ng mL\({}^{-1}\) (corresponding to 0.01-10 ug kg\({}^{-1}\)); for OTA, in the range of 0.01-10 ng mL\({}^{-1}\) (corresponding to 0.2-200 ug kg\({}^{-1}\)); for FB1, FB2, HT-2 toxin, T-2 toxin and ZEA, in the range of 0.1-100 ng mL\({}^{-1}\) (corresponding to 2-2000 ug kg\({}^{-1}\)); and for DON, 3-AcDON, 15-AcDON and NIV, in the range of 0.4-400 ng mL\({}^{-1}\) (corresponding to 8-8000 ug kg\({}^{-1}\)). The limit of quantification was set at 0.04 ug kg\({}^{-1}\) for AFLB1 and AFLG1; 0.01 ug kg\({}^{-1}\) for AFLB2 and AFLG2; 1 ug kg\({}^{-1}\) for OTA; 10 ug kg\({}^{-1}\) for FB1 and FB2; 1 ug kg\({}^{-1}\) for HT-2 toxin and T-2 toxin; 2 ug kg\({}^{-1}\) for ZEA; 4 ug kg\({}^{-1}\) for 15-AcDON; and 40 ug kg\({}^{-1}\) for DON, 3-AcDON and NIV. Estimation of LOD for each mycotoxin was done via calibration approach according to the \"Guideline for the estimation of LOD and LOQ for the measurement of contaminants in feed and food\" [29] based on linear multi-point calibration curve, including lowest calibration level (LCL), characterized by R\({}^{2}\geq 0.995\). LOQ was estimated as equivalent to 3.3 \(\times\) LOD. It was assumed for simplicity that LOQ for most mycotoxins is equivalent to the level of lowest calibration level (LCL), while for HT-2 toxin, T-2 toxin and 15-AcDON as equal to 1/2 LCL.