Development of analytical methods to study the effect of malting on levels of free and modified forms of Alternaria mycotoxins in barley.

A liquid chromatography tandem mass spectrometry (LC-MS/MS) multi-mycotoxin method was developed for the analysis of the Alternaria toxins alternariol (AOH), alternariol monomethyl ether (AME), tentoxin (TEN), altertoxin I (ATX I), altertoxin II (ATX II), alterperylenol (ALTP), and altenuene (ALT), as well as the modified toxins AOH-3-glucoside (AOH-3-G), AOH-9-glucoside (AOH-9-G), AME-3-glucoside (AME-3-G), AOH-3-sulfate (AOH-3-S), and AME-3-sulfate (AME-3-S) in barley and malt. The toxin tenuazonic acid (TeA) was analyzed separately as it could not be included into the multi-mycotoxin method. Quantitation was conducted by using a combination of stable isotope dilution analysis (SIDA) for AOH, AME, and TeA, and matrix-matched calibration for all other toxins. Limits of detection were between 0.05 µg/kg (AME) and 2.45 µg/kg (ALT), whereas limits of quantitation ranged from 0.16 µg/kg (AME) to 8.75 µg/kg (ALT). Recoveries between 96 and 107% were obtained for the analytes when SIDA was applied, while recoveries between 84 and 112% were found for analytes quantified by matrix-matched calibration. The method was applied for the analysis of 50 barley samples and their respective malts from the harvest years 2016-2020 for their mycotoxin content, showing the overall potential of toxin formation during the malting process. The toxins ALTP and ATX I were mainly found in the malt samples, but not in barley.