Studies on toxigenic fungi in roasted foodstuff (salted seed) and halotolerant activity of emodin-producing Aspergillus wentii.

Commercial roasted salted peanuts (3% NaCl), popcorn (1% NaCl), summer-squash (9% NaCl), sunflower (3% NaCl) and wild-melon (3% NaCl) seeds are polluted with fungi, mostly Aspergillus flavus, A. niger, Penicillium chrysogenum, P. corylophilum and Rhizopus stolonifer. Contamination of popcorn with the fungi is about 10 times higher than in the other foods. These fungi, common also on unsalted seeds, are significantly inhibited in seeds (30% moisture content) treated with 9-21% NaCl. The halotolerant A. wentii represents the main fungus recovered from seeds treated by 15-21% NaCl. 9% NaCl stimulated emodin production by A. wentii on peanut and citrinin production by P. chrysogenum on popcorn and sunflower. Aflatoxin, citrinin and emodin production on popcorn persisted up to 15% NaCl. Popcorn is thus strongly susceptible to fungal invasion and toxin pollution. The halotolerance of A. wentii was confirmed by its strong permanent growth in liquid medium at up to 15% NaCl. At 3% NaCl the mycelial growth and nitrogen content increased while the level of emodin and lipid production decreased. CO2 evolution strongly increased at 9-15% NaCl as a characteristic of A. wentii salt tolerance. Emodin inhibited seed viability and the inhibition dose for 50% reduction (LD50) was 65 mg/L for popcorn and 45 mg/L for sunflower.