Abstract
Ochratoxin A (OTA) is one of the most abundant food-contaminating mycotoxins. Besides their high toxicity, mycotoxins are highly stable to physical, chemical or biological detoxification. Therefore, the treatment with cold atmospheric plasma could be one approach to reduce the amount of mycotoxins in different products. The aim of this study was to determine the influence of cold atmospheric plasma on the inactivation of Aspergillus niger and Penicillium verrucosum inoculated on barley and their production of OTA. Inoculated barley was treated with plasma generated by dry air, CO2 or CO2 + O2 for 1 or 3 min and stored for up to two weeks at 9, 25, or 37°C. Three minutes of air plasma treatment effectively significantly reduced the total mold count of both microorganisms by 2.5–3 log cycles. The production of OTA from A. niger was only low, therefore the treatment effect was indistinguishable. The treatment of P. verrucosum on barley after an incubation of five days using a CO2 + O2 plasma resulted in a reduction of the OTA content from 49.0 (untreated) to 27.5 (1 min) and 23.8 ng/g (3 min), respectively. In contrast, CO2 plasma caused an increase of the OTA amount from 49.0 (untreated) to 55.8 (1 min) and 72.9 ng/g (3 min). Finally, the use of air plasma resulted likewise in a decrease of the OTA concentration from 56.9 (untreated) to 25.7 (1 min) and 20.2 ng/g (3 min), respectively. Reducing the incubation time before the treatment to 24 h caused in contrast an increase of the OTA content from 3.1 (untreated) to 29.1 (1 min) and 20.7 ng/g (3 min). Due to the high standard deviation, these changes were not significant, but the tendencies were clearly visible, showing the strong impact of the plasma gas on the OTA production. The results show, that even if the total mold count was reduced, under certain conditions the OTA amount was yet enhanced, probably due to a stress reaction of the mold. Concluding, the plasma gas and incubation conditions have to be considered to allow a successful inactivation of molds and in particular their toxic metabolites.
Highlights
When crop is not stored properly after harvest, especially when moisture content and temperature are too high, different molds like, e.g., Aspergillus niger and Penicillium verrucosum can grow on its surface
After inoculation of barley with a mycelium suspension of Aspergillus niger followed by a plasma treatment with air, CO2 or 80% CO2 + 20% O2 as process gasses for 1 or 3 min, the amount of produced Ochratoxin A (OTA) directly and after storage at 37◦C for one week was measured using HPLC
One exception was the plasma treatment using CO2 as process gas for 3 min, where the OTA concentration slightly increased after one week from 0.15 ± 0.1 ng/g in the untreated grains to 0.20 ± 0.08 ng/g after 3 min plasma
Summary
When crop is not stored properly after harvest, especially when moisture content and temperature are too high, different molds like, e.g., Aspergillus niger and Penicillium verrucosum can grow on its surface. Both molds belong to the family Trichocomaceae. Penicillium verrucosum (P. verrucosum) belongs to the genus Penicillium and has important implications in food, for grains and other cereal crops on which it grows predominantly in Northern Europe It has a white mycelium with green conidia, which have the ability to germinate at temperatures between 0 and 31◦C with a temperature optimum between 21 and 23◦C (Domsch et al, 1980). At temperatures between 10 and 25◦C and a water activity (aw) of around 0.95, ochratoxin A (OTA) synthesis of some P. verrucosum strains occur (Lund and Frisvad, 2003; Cairns-Fuller et al, 2005)
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