## 2 Materials and Methods
### LC-MS/MS Analysis of Mycotoxins  
Sample extraction was done according to the method developed by [PERSON] et al. (2008) [28] with slight changes. Ground sample material (5 g) was shaken in 50 mL plastic falcon tube with 5 mL of water for 30 min (Multi Reax, Heidolph, Schwabach, Germany). Then, 15 mL of acetonitrile were added and the sample was shaken on horizontal shaker (HS 501 digital, IKA-Werke GmbH & CO. KG, Staufen, Germany) for 2 h and centrifuged twice at 4143\(\times\)\(g\) (Rotina 420R, Hettich Zentrifugen, Tuttlingen,Germany) for 3.5 min at \(15\pm 1\)\({}^{\circ}\)C. A 200-\(\upmu\)L clear extract was pipetted into a 2-mL chromatography vial, and 750 \(\upmu\)L of LC mobile phase (95% A and 5% B) and 50 \(\upmu\)L of internal standard (ILS) were added allowing to obtain 20-fold dilution minimizing the matrix effect. The method was validated with both the tested matrices as well as the purchased European Reference Materials (ERMs). Recovery experiments were performed to evaluate the method accuracy. The recoveries were in the range of 70-120% and precision (RSD) \(\leq\)20%. The suitability of the method for testing was confirmed in 2 rounds of proficiency tests organized by TestQual Proficiency Testing Schemes (Murcia, Spain), TestQual 85 and TestQual 88, as well as in Romer Labs Check Sample Survey (CSSMY018-M20161 DZO). The LC-MS/MS system consisting of an Eksigent expert ultraLC 100-XL (Eksigent Technologies, Dublin, CA, USA) coupled to triple quadrupole mass spectrometer QTRAP 6500 (AB Sciex Instruments, Foster City, CA, USA) was used for the analysis of the mycotoxins. A 10-\(\upmu\)L aliquot (cooled to \(8\pm 1\)\({}^{\circ}\)C) was injected on Kinerex core-shell C18 100 A (100 mm \(\times\) 2.1 mm, 2.6 \(\upmu\)m) column (Phenomenex, Torrance, CA, USA) at 40 \({}^{\circ}\)C column temperature. The gradient was composed of solvents A (0.1% formic acid and 5 mM ammonium formate in water) and B (0.1% formic acid and 5 mM ammonium formate in methanol) at a flow rate of 0.5 mL min\({}^{-1}\). The gradient elution was started with 98% A and 2% B and held for 1.0 min, then rising linearly to 2% A and 98% B in 9 min and held for 3.0 min. The composition of the mobile phase was returned to starting condition over 0.1 min, followed by a column re-equilibration phase of 2.9 min. The total time of data acquisition was 16.0 min. The MS/MS 6500 QTRAP was operated in electrospray ionization positive (ESI+) and negative (ESI-) mode, at capillary voltage of 4500 or \(-\)4500 V, the desolvation temperature of 500 \({}^{\circ}\)C, the entrance potential (EP) of 10 or \(-\)10 V, with nitrogen as the curtain (CUR), nebulizer (GS1) and auxiliary (GS2) gas, at a pressure of 30, 60 and 50 psi, respectively. Nitrogen was also used as collision gas. Ionization and MS/MS collision energy settings were optimized while continuously infusing mycotoxin solution at a flow-rate of 100 \(\upmu\)L min\({}^{-1}\) via a syringe pump. For each mycotoxin, the parent and two daughter ions were selected and the first one was used for quantification and the second one for confirmation. Data acquisition was performed in the multiple reaction monitoring mode (MRM). LC-MS/MS chromatograms of representative samples are shown in Figure S8. Analyst Software version 1.6.2 and MultiQuant Software version 3.0.2 (AB Sciex) were used for data acquisition and processing. Retention time (RT), precursor and product ions monitored and optimized collision energy, declustering potential, collision energy and cell exit potential for the ESI+ and ESI- ionization mode are demonstrated for each mycotoxin in Table S1.