Mycotoxines et champignons dans les grains de sorgho commercialisé en Tunisie: incidence et profils écophysiologiques

In this thesis, we have studied the occurrence of aflatoxin B1, ochratoxin A and zearalenon in 64 sorghum samples purchased from Tunisian market. Mycotoxins extraction was carried with organic solvents and their determination was achieved by HPLC. The results showed that 59.37%, 37.5% and 32.81% of samples were contaminated with aflatoxin B1, ochratoxin A and zearalenone, respectively. The co-occurrence of these three mycotoxins was observed in 12.5% of total samples. The mycobiota of sorghum samples was determined in three times. The first step was the quantitative fungal count using “Direct Plating” method, later the internal mycobiota was determined by microscopic observation of colonies mold and finally, fungal identity was confirmed by molecular characterization. The mycotoxinproducing ability was verified by extraction of the mold colonies with methanol and detection by HPLC. The results showed the predominance of the genera Fusarium, Aspergillus and Alternaria. Aspergillus flavus was the most common species in sorghum grain among the section Flavi, while Aspergillus niger aggregates were the most dominant in the section Nigri. Among Fusarium species, Fusarium section Liseola and the Fusarium incarnatum-equiseti complex were the most dominant in sorghum. The study of the mycotoxin-producing ability showed that 40.24% of Aspergillus flavus, 4.61% of Aspergillus section Nigri and 11.09% of Fusarium isolates produce aflatoxin B1, ochratoxin A and zearalenon, respectively. To develop mycotoxin minimization and prevention procedures, ecophysiological profils of Aspergillus flavus, Aspergillus tubingensis and Fusarium incarnatum were studied. The effects of water activity, temperature and incubation time on mycelia growth and mycotoxin production were studied. According to our results, Aspergillus flavus grew and produced more aflatoxin B1 at 37 °C and 0.99 aw. Optimal conditions for Aspergillus tubingensis were 0.99 aw and 37 °C, but maximum production of ochratoxin A occurred at 0.97 aw and 25 °C, while Fusarium incarnatum grew more at 25 °C and 0.99 aw but optimal conditions for zearalenone accumulation cannot be determined. However, we did not find publications on ecophysiological profile of Fusarium incarnatum species. This study is an approach that seeks to understand the physiology of fungal species producing mycotoxins under different climatic conditions in order to set limits for the control fungal spoilage and mycotoxin accumulation in cereals.

Full-text available at: https://www.tesisenred.net/handle/10803/400373