Aflatoxins: production of the toxins on rice-corn steep medium according to some cultural conditions.

Rice powder-corn steep (RC) medium proved to be the most suitable among 6 nutrient liquid media for both aflatoxin formation and mycelial growth by the Aspergillus flavus strain No. 182, isolated locally. The production of aflatoxins by the mould was studied in relation to some cultural conditions on RC medium. Highest aflatoxin yields (2527 microgram/50 ml) by A. flavus were attained using rice (5%, w/v) + corn steep (4%, w/v), at initial pH level of 4,25 degree C and 6 days incubation. The initial pH levels at either extreme of the range used (3 and 11), and temperatures of incubation below 20 degree C or above 40 degree C were inhibitory to mould growth and aflatoxin formation. The ratio of aflatoxin B1 to G1 varied with different cultural conditions. The aflatoxin content of the mycelia highly exceeded that of the culture filtrates.

Inhibition of aflatoxin production inAspergillus flavus by natural coumarins and chromones.

The activities of three natural coumarins, xanthotoxin and bergapten (fromAmmi majus, Umbelliferae) and psoralene (fromFicus cycomorus, Moraceae), were tested against mycelial growth and aflatoxin production of a toxigenic strain ofAspergillus flavus grown in a rice/corn steep liquor medium. Two other natural chromones, khellin and visnagin (fromAmmi visnaga) were also compared. Complete inhibition of aflatoxin release occurred with either xanthotoxin or khellin at 5 mM. The other three compounds also at 5 mM reduced aflatoxin to 12 to 16% of its original concentration. The mould growth was only slightly inhibited by all the compounds used.

Formation of aflatoxins by some Egyptian Aspergillus flavus strains.

In all the fifteen investigated Aspergillus flavus and A. parasiticus strains the maximum quantities of aflatoxins, produced on rice powder-corn steep (RC) medium, ranged from 1.17 to 23.29 times as much as those produced on yeast extract-sucrose (YES) medium. The shake cultures lowered aflatoxin formation. The maximum yields of aflatoxins did not coincide with maximum fungal growth. In most A. flavus strains investigated, the total aflatoxin content of the mycelia highly exceeded that of the culture filtrates.

Inhibition of aflatoxin formation by some spices.

The effects of black pepper, cinnamon, peppermint, cumin, ginger and clove on growth and aflatoxin formation of Aspergillus flavus were studied in rice powdercorn steep (RC) medium. The effects of the first five spices were judged to be inhibition of aflatoxin formation rather than of mycelial growth. Clove completely inhibited both mycelial growth and aflatoxin formation at a concentration above 0.1%. No aflatoxin was produced when cumin and mint levels of 5% and 10% were used. Black pepper and ginger levels of 10% decreased aflatoxin formation by 100%. Higher concentrations of cinnamon, mint, cumin and ginger stimulated mycelial growth.

Production of ochratoxins by some Egyptian Aspergillus strains.

In all the investigated Aspergillus ochraceus and A. alliaceus strains the maximum quantities of ochratoxins produced on yeast extract-sucrose (YES) medium exceeded that detected on wheat solid medium except A. ochraceus 67. The shake cultures lowered ochratoxins formation. The maximum yields of ochratoxins did not coincide with maximum fungal growth. In most A. strains investigated, the total ochratoxin contents of the culture filtrates highly exceeded that of the mycelia.