الفهرس 
AbstractOnly 14 pages are availabe for public view
 |  | from | 161 |  |  |
| | | from | 161 | | |
Abstract
The current study was focused on assessment of fungal and mycotoxin contamination in 51 samples of rice grains ready for human consumption in Minia Governorate, Egypt. Prevalence of actinomycetes was also evaluated. Enzymatic activities of contaminating fungal strains were tested with special focus on amylases, L-asparaginase and l- arginase. The following results were achieved: Aspergillus was the most common genus on both DRBC and DG18. Aspergillus flavus was the most common species, A. candidus and A. niger were moderately encountered, the genus Penicillium showed high incidence. Penicillium aurantiogriseum, P. chrysogenum, P. citrinum, P. duclauxii, P. glabrum, P. islandicum and P. oxalicum showed low incidence. Each of Alternaria and Cladosporium showed moderate incidence. Low number of rice samples was contaminated with Lichtheimia corymbifera, the osmophilic species Aspergillus chevalieri, A. montevidensis and A. rubrum showed moderate frequency on DG18 but they appeared with rare incidence on DRBC. Aspergillus niger which showed high frequency on DG18, had moderate incidence on DRBC. Each of A. clavatus, A. fumigatus and A. ochraceus showed low frequency on DG18 but they were rare on DRBC.
Molecular techniques were used for identification of six fungal strains which were generally active producers of amylase, L-asparaginase or L- arginase. The ITS region of rRNA gene confirmed the identification of the following strains: Trichoderma harzianum isolate BS 29 (accession number OP521774), Aspergillus fumigatus strain AUMC 11372 (OP521772), Aspergillus fumigatus isolate BS 38 (OP521773), Aspergillus ochraceus strain 11035 (MF075153) and Aspergillus flavipes strain AUMC 11390 (MZ066617). Beta tubulin gene was sequenced for genetic identification of Aspergillus terreus BS45 (OP613101). Streptomyces species was the only representative actinomycetous organism isolated from 6 rice samples on starch nitrate agar and yeast malt agar. Molecular technique was used for identification of one actinomycete isolate, comparison of the16S rRNA sequence of this isolate against the GenBank database indicated that this isolate was Streptomyces genus and shared 99.85% similarity percent with species Streptomyces flocculus accession no. NR_041100.1 followed by species Streptomyces albus accession no. 1NR_118467.1. HPLC analysis proved the presence of aflatoxins in ten selected samples and the highest quantity of total aflatoxins (1116.3335 ng/ml equivalent to11163.335 ng/kg) was obtained from sample no.9. This sample exhibited also the highest values of aflatoxin B1 (1045.038 ng/ml) and contained aflatoxin G1 and B2 (53.87396 and 20.79412 ng /ml respectively). Relatively high quantities of aflatoxins were detected in 4 samples. All tested rice samples were contaminated with Aspergillus flavus and A. flavus var. columnaris or one of them. Ochratoxin-A was detected in chloroform extracts of 3 rice samples at levels ranging from 1.885845 to 6.518265 ng/ml. These samples produced Aspergillus ochraceus or A. niger when cultured on agar media. HPLC analysis showed that all tested samples contained 9.303922–26.42157 ng/ml aflatoxin B2 and aflatoxin G1 at levels of 3.889767–53.87396 ng/ml. Aflatoxin G2 was detected only once in sample no. 10 at a concentration of 0.56 ng/ml.
A total of 62 fungal isolates belonging to 45 species were tested for their ability to produce amylase, L-asparaginase and L-arginase enzymes in agar media. The most active amylase producers involved 8 strains of Aspergillus in addition to Trichurus spiralis, L- asparaginase was produced by 60 fungal strains (96.77%) and most of which were high producers. Fifty fungal strains representing 80.65% of tested fungi showed L-arginase activity in solid cultures. High L-arginase producers comprised 16 strains distributes in 7 genera, among the 5 fungal strains cultured in submerged fermentation (SmF) for amylase activity, Penicillium thomii AUMC 11391 was the most active and displayed the highest relative activity and specific activity. L-asparaginase from Aspergillus ochraceus AUMC 11382, exhibited the highest activity over other tested strains. Aspergillus flavipes AUMC 11390 was the most potent strain generating L-arginase. The most suitable conditions for maximum amylase activity were pH 5.0 and 35ºC (18.3 and IU/gds and 60 IU/gds). Similarly, L-asparaginase was produced with relatively high yield (5.1 g/L medium). The enzyme proved to be active over a wide range of pH values. The highest specific activity was achieved at pH 5.0 and 35℃ (9231.2 IU/mg).