Resumo

Mycotoxins can be a significant concern for maltsters and brewers in many regions of the world, and deoxynivalenol (DON) associated with malting barley appears to be most common. As a consequence, deliveries of malting barley are routinely screened for DON in regions in which Fusarium Head Blight (FHB) is common. The presence of the conjugated form, DON-3-glucoside (DON3G), in cereal grains was first reported in 2005. This raised concern, as it is not detected by routine methodology, thus becoming known as a masked mycotoxin. In a previous study, involving barley from multiple crop years, we demonstrated that DON3G is rarely present in excess of 20 mol% of the DON. However, the situation in malted barley can be quite different with levels of DON3G often far exceeding those of the DON. The aim of the current was to determine the relationship between barley DON levels, growth of Fusarium graminearum during malting, and levels of DON3G observed in finished malt. Twenty FHB-positive and four FHB-negative samples were malted under several different conditions. DON was determined by GC-ECD and DON3G by UPLC QTOF MS. The biomass of Fusarium sp. on barley and malt samples was assessed using real-time PCR with a fluorogenic TaqMan probe. A triazole-based fungicide was added to one malting subset in order to inhibit Fusarium growth during germination. DON levels were observed to increase by an average of 2.2-fold during malting (3.1 to 6.8 mg/kg), although there was considerable variation. On the other hand levels of DON3G averaged 36.9 mg/kg, representing an average increase of 48-fold. The balance between DON and DON3G during malting is appears to be complex, with some DON being lost during processing, additional DON being formed in association with fungal growth, and then a portion of this being converted to the conjugated form via the action of barley UDP-glucosyl transferases. These results clearly demonstrate that maltsters and brewers must be cognizant of DON3G and the possibility for its formation during malting.