الفهرس 
Chemical and physical propertiesOnly 14 pages are availabe for public view
 |  | from | 160 |  |  |
| | | from | 160 | | |
Abstract
Aflatoxins are a group of structurally related mycotoxins, aflatoxins are toxic metabolites mostly produced by many fungal species as Aspergillus flavus and Aspergillus parasiticus in cereal grains, groundnuts, corn and rice. They are considered as mutagenic, teratogenic, carcinogenic and immunosuppressive compounds.
This study aimed to find an antifungal substance of some selected bacterial strains to be used in biological control of mycotoxins.
In this study three bacterial strains : Streptococcus thermophilus, Bacillus subtilis and Lactobacillus bulgaricus were used to detect their antifungal activity against Aspergillus flavus and Aspergillus parasiticus in different conditions of pH, temperature, length of incubation period and growth on different types of media.
Also the biostability of the antifungal substances produced by bacteria was studied under different conditions as heating at 80, 100 ºC and autoclaving at 121 ºC.
1- pH values: four pH values were tested (4, 7, 9 and 10), when A. flavus co- cultivated with Streptococcus thermophilus, Bacillus subtilis and Lactobacillus bulgaricus, the antifungal activity appeared at 4, 10 and 4 respectively while with A.parasiticus appears at 9, 10and 4 respectively.
2- Temperatures: four temperatures were studied (4, 25, 30 and 37 ºC), when A. flavus co- cultivated with Streptococcus thermophilus, Bacillus subtilis and Lactobacillus bulgaricus, the antifungal activity appeared at 25 ºC for Streptococcus thermophilus and Bacillus subtilis and at 37 ºC for Lactobacillus bulgaricus, while with A.parasiticus it appears at 4, 4and 25 ºC respectively.
3- Incubation periods: Four incubation periods were tested (4, 7, 10 and 14days), Streptococcus thermophilus, Bacillus subtilis and Lactobacillus bulgaricus, showed antiaflatoxigenic activity at 4, 14 and 14 days when simultaneously grown with A. flavus but with A.parasiticus they showed antiaflatoxigenic activity at 10, 14 and 7 days respectively.
4- Culture media: Streptococcus thermophilus, Bacillus subtilis and Lactobacillus bulgaricus, showed antiaflatoxigenic activity when grown with A. flavus and A.parasiticus on yeast extract sucrose medium but the activity decreased with potato dextrose borth.
5- Thermal stability: the antifungal metabolites of the three bacterial strains are thermostable, not affected by heating or autoclaving.
6- Protein electrophoresis: the antifungal metabolites of the three bacterial strains were precipitated using 40% ammonium sulphate then centrifugated at 5000 rpm for 15 minutes then suspended in phosphate buffer saline (PBS) and protein electrophoresis carried out to detect their molecular weight.