Occurrence of Alternaria secondary metabolites in milling oats and its de-hulled fractions from harvest years 2017 to 2021

In this study, secondary metabolites produced by Alternaria were investigated for their presence in milling oats. For this purpose, pre-cleaned milling oat samples (n = 193), intended for human consumption, out of harvest years 2017 to 2021 originating from different northern European countries were analysed by LC-MS/MS. Alternariol and alternariol methyl ether were positively identified in 38% of the samples with mean values of 2.1 mu g/kg and 1.2 mu g/kg, respectively. The highest concentrations of 50.5 mu g/kg alternariol and 24.2 mu g/kg of alternariol methyl ether were detected in a Latvian sample. Tenuazonic acid was found in 45% of all samples, with a mean concentration of 28.9 mu g/kg and a maximum concentration of 1430 mu g/kg, also in a Latvian sample. Tentoxin was detected in 49% of all samples with a mean value of 1.7 mu g/kg. The Alternaria metabolite most frequently detected in 96% of all samples was infectopyrone with a mean concentration of 593 mu g/kg and a maximum value reaching up to 3990 mu g/kg in a German sample. In addition, eight oat samples were selected to investigate to what extent the Alternaria metabolites are distributed between the oat hulls and the oat kernels. After de-hulling, approximately 23% of Alternaria metabolites were found in the remaining oat kernels. According to the results, alternariol, infectopyrone and altersetin were present in the kernels with the lowest proportion of 10%-20% on average, respectively. The values for tentoxin showed that about 60% of tentoxin was contained in the hulls, while almost 40% remained in the oat kernel. This suggests that potential health risks posed by Alternaria secondary metabolites and metabolites of other fungal genera in milling oats can be reduced by de-hulling.