Lipoperoxidation and Aflatoxin Biosynthesis by Aspergillus parasiticus and A. flavus
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The amount of aflatoxin produced by Aspergillus flavus and Aspergillus parasiticus grown on various aged and non-aged seeds, kept at suitable conditions of temperature and moisture, is particularly related to the peroxide numbers of the seed oils. The addition of synthetic hydroperoxides to the cultures greatly increased aflatoxin production.Keywords:
Aspergillus parasiticus
ycological examination of 500 samples of animal feeds and feed ingredients for Aspergillus flavus and Aspergillus parasiticus revealed that 180 (36%) samples yielded isolates of Aspergillus flavus and 65 (13%) samples gave isolates of Aspergillus parasiticus. Testing of the same samples for AFB1 contamination showed that 99 samples (19.8%) contained AFB1 at a rate of 125 ppb, 45 samples (9%) at a rate of 25-50 ppb, 32 samples (6.4%) at a rate of 101-200 ppb and 19 samples (3.8%) contained aflatoxin B1 at a rate of 201-2000 ppb. Screening of isolated strains of Aspergillus flavus and Aspergillus parasiticus for aflatoxin B1 production by culturing on YES medium supplemented with 0.019% P-cresol revealed that 81 (45%) out of 180 isolates of Aspergillus flavus and 16 (24.62%) out of 65 isolates of Aspergillus parasiticus produced aflatoxin B1. Testing the ability of 4 Lactobacillus strains for removal of aflatoxin B1 from liquid media after physical and chemical treatments revealed that the acidic and heat treatments of bacterial pellets significantly enhanced their ability to bind aflatoxin B1 but heat treatment was not as effective as acidic treatment. Screening the ability of either intact mycelium or fragmented mycelium or culture cell - free system of non - aflatoxin B1 producing Aspergillus flavus and Aspergillus parasiticus indicated that fragmentation increased the ability of tested strain to degrade aflatoxin B1. Culture cell free system showed the highest percent of aflatoxin B1 degradation. Aspergillus flavus showed higher percent of degradation than Aspergillus parasiticus.
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The influence of pyridazinone herbicides on aflatoxin production by Aspergillus flavus and A. parasiticus was studied in liquid media. Mycelia production was not affected by 20, 40, or 60 micrograms of herbicide per ml; however, aflatoxin production by A. parasiticus was higher in media with herbicide, whereas A. flavus produced lower aflatoxin levels.
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The amount of aflatoxin produced by Aspergillus flavus and Aspergillus parasiticus grown on various aged and non-aged seeds, kept at suitable conditions of temperature and moisture, is particularly related to the peroxide numbers of the seed oils. The addition of synthetic hydroperoxides to the cultures greatly increased aflatoxin production.
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Aflatoxins are polyketide secondary metabolites that are produced by certain fungal species in the Aspergillus section Flavi, particularly Aspergillus flavus and Aspergillus parasiticus which contaminate human food as well as animal feed. These are among the most carcinogenic substances known. Due to the toxic and carcinogenic properties of aflatoxins, there is a need to develop reliable methods to detect the presence of aflatoxigenic Aspergilli in contaminated food and feed. Not all Aspergillus strains are able to produce aflatoxins. It requires a detection methodology which can specifically distinguish between the aflatoxin producing and nonproducing strains of Aspergillus. Present communication reports validation of a PCR based detection system based on three genes viz., nor-1, apa-2 and omt-1 involved in aflatoxin biosynthesis, that can specifically distinguish the two aflatoxin producing species viz. Aspergillus flavus ,and Aspergillus parasiticus from non-producers i.e., A. niger, A. fumigates and A. oryzae.
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Nyjer seeds are oil rich (35-40% oil content) seeds of the plant Guizotia abyssinica , which is closely related to sunflower. They are pressed mechanically for cooking oil in Ethiopia and elsewhere. The remaining deoiled cake, which contains approximately 10% oil is commonly used as animal feed. This study investigated the effect of water activity and temperature on the growth and aflatoxin production of the four main forms of aflatoxin (B 1 , B 2 , G 1 and G 2 ) by Aspergillus flavus and Aspergillus parasiticus on ground nyjer seed with 10% oil. The ground nyjer seeds were adjusted to different water activity a w levels (0.82, 0.86, 0.90, 0.94 and 0.98 a w ) and incubated at 20, 27 and 35 °C, up to 30 days. Our results show that A. flavus and A. parasiticus had similar growth patterns in which the slowest fungal growth occurred on ground seeds with 0.86 a w at 20 °C. There was no fungal growth for either A. flavus or A. parasiticus at 0.82 a w . The most rapid growth conditions for A. flavus and A. parasiticus were 0.94 a w at 35 °C, and 0.94 a w at 20 °C, respectively. Aspergillus flavus produced aflatoxins (13 μg/kg aflatoxin B 1 ) only on seeds with 0.94 a w at 27 °C, while A. parasiticus produced high levels of aflatoxins under several conditions; the highest concentrations of aflatoxin B 1 (175 μg/kg) and AFG 1 (153 μg/kg) were produced on deoiled ground seeds with 0.94 a w at 27 °C. It is likely that storing ground deoiled nyjer seeds with a water activity up to 0.82 a w at 20 °C will reduce fungal growth aflatoxin production.
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The population of Aspergillus flavus and the amounts of aflatoxins in maize ears and kernels collected from 4 areas in Thailand in 1987 were studied. Eleven maize ear samples from the randomly selected fields showed no infection of A. flavus and very low amount (9 ppb) of aflatoxin B1 was found in only one sample. Similarly, the infection of A. flavus in 6 maize ear samples collected from farmers' and middlemen's storages was very low (0-3% of kernels from the ear); two samples of them were positive for aflatoxins (aflatoxin B19 and 58 ppb). However, all 15 maize kernel samples collected from the middlemen's storages were found to be highly contaminated with A. flavus and aflatoxins. There were clearly less contaminations of A. flavus and aflatoxins in the maize ear than those in the kernels.
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Aflatoxins, which are well-known to be mutagenic, carcinogenic, teratogenic, hepatotoxic and immunosuppressive, also inhibit several metabolic systems. Aflatoxins are biologically active secondary metabolites produced by certain strains of Aspergillus parasiticus, Aspergillus nominus and Aspergillus flavus. Many different substances, such as essantial oils, flavanoids, could inhibit the aflatoxin production and growth of Aspergillus. In this study, aflatoxins biosyntesis, aflatoxins damaged and aflatoxins with essential oils interaction are evaluated.
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