engleski

Distribution of zearalenone in malt barley fractions dependent on Fusarium graminearum growing conditions

Aim of this work was to determine zearalenone (ZEA) distribution in main fractions of barley malt dependent on incubation time, humidity and temperature. Barley was malted and dried according to the MEBAK standard procedure and then sterilized in autoclave. Water activity was adjusted to 0.95 and 0.98, respectively. Samples were inoculated with mycelium discs of Fusarium graminearum (CBS 110250) and incubated at 20°C and 30°C. Following incubation for 17, 26, 34 days, malted barley was dried and grain was milled and sieved to obtain flour and bran. The third fraction was made up of previously detached germ and rootlets. Samples were extracted with a mixture of acetonitrile and water followed by immunoaffinity clean-up of ZEA. Analyses were carried out by LC-MS/MS. ZEA levels were highest in bran from barley malt incubated at aw 0.98, 20°C for 26 days (96.88 ± 0.88 mg/kg d.m.) with significantly (p<0.01) lower levels in germ (45.70 ± 4.91 mg/kg d.m.) and flour (35.76 ± 7.55 mg/kg d.m.). Similar pattern was noted at water activity 0.95 and 20°C. Incubation at 30°C resulted in generally lower ZEA levels in fractions regardless of aw. A consistent decrease of final ZEA concentration over incubation period (17 vs. 34 days) was detected in bran and germ, as opposed to flour levels, at both temperatures and aw 0.95. On the other hand, aw 0.98 effected a temporal decrease in ZEA germ concentration and increases in bran and flour levels at both temperatures. Examination of the effect of humidity on ZEA accumulation revealed that aw 0.95 brought about a significant drop in mycotoxin levels in all fractions at 20°C with increasing incubation length. The lower aw also boosted flour ZEA levels at 30°C, while, opposed to the 20°C results, aw 0.98 failed to substantially stimulate the mycotoxin accumulation at this temperature. The study indicates the importance of storage conditions on ZEA distribution among commercially relevant seed fractions of malted barley and gives insights on manipulations which might enable their efficient control.

Fusarium graminearum; zearalenone; malt

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