Mycoflora and mycotoxin of hazelnut (Corylus avellana L.) and walnut (Juglans regia L.) seeds in Egypt.
Fifty-one spp. and 3 varieties from 20 genera of fungi were identified from 20 samples each of hazelnut and walnut seeds on glucose- and 40% (W/V) sucrose-Czapek's agar at 25°C and 45°C. The most common mesophiles were Aspergillus flavus, A. fumigatus, A. niger, Cladosporium cladosporioides, C. herbarum, Penicillium chrysogenum, P. citrinum and P. oxalicum. Fusarium (represented by F. equiseti, F. moniliforme and F. oxysporum) was recovered from walnut seeds in moderate frequency (on glucose Czapek's agar). Eurotium spp.(E. amstelodami, E. chevalieri, E. repens and E. rubrum) were completely absent on glucose agar, but were isolated in high numbers from the two seed types on 40% sucrose-Czepek's agar. Aspergillus fumigatus and Rhizomucor pusillus were the most common thermophilic fungi in hazelnut and walnut seeds on glucose agar at 45°C. Humicola grisea var. themoidae and Thermoascus aurantiacus were rarely found in walnuts. The nut samples were assayed for natural occurrence of aflatoxins B1, B2, G1 and G2, citrinin, ochratoxin A, patulin, sterigmatocystin, zearalenone, T-2 toxin and diacetoxyscirpenol using thin layer chromatography. Aflatoxin was detected in 90% of hazelnut samples (25-175 μg/kg) and 75% of walnut samples (15-25 μg/kg). Zearalenone was detected in one sample of walnut (125 μg/kg). This is the first report of the presence of zearalenone in walnut. The other mycotoxins were not detected.