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العنوان
Prevention of mycotoxigenic molds growth and inactivation of their mycotoxins in food through the application of irradiation and other technologies /
المؤلف
Abd El-Kader,Reham Mohamed Mohamed.
هيئة الاعداد
باحث / Reham Mohamed Mohamed Abd El-Kader
مشرف / Khayria Abd El-Ghany Youssef
مشرف / Ali Ahmed Ibrahim Hammad
مشرف / Hanan Hassan Abd El Khalek
تاريخ النشر
2019
عدد الصفحات
211p.:
اللغة
الإنجليزية
الدرجة
الدكتوراه
التخصص
علوم النبات
تاريخ الإجازة
1/1/2019
مكان الإجازة
جامعة عين شمس - كلية العلوم - الميكروبيولوچ?
الفهرس
Only 14 pages are availabe for public view

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Abstract

Contamination of agricultural products such as grains, nuts and other crops with mycotoxin producing molds and their mycotoxins is of importance concern worldwide. Aflatoxins produced by Aspergillus flavus and A.parasiticus are the most potent mycotoxins. Among the four aflatoxins (B1, B2, G1, G2) present in a wide variety of food and feed, AFB1 is considered the most potent carcinogenic substance. Various methods of preservation have been applied to arrest the growth of mycotoxigenic molds and reduce the level of their mycotoxins in food and feed, but none of these method offers complete control of them.
 Several fungal isolates were isolated from sorghums and peanuts, these fungal isolates belonged to four genera: Aspergillus, Penicillium, Fusarium and Rhizopus. Aspergillus genus was found to be the most predominant among other isolated fungal genera.Five species of this genus were identified :A.niger, A.flavus, A.parasiticus, A.terrus and A.fumigatus.
 Twenty six isolates of Aspergillus flavus isolates were isolated (10 from sorghums and 16 from peanuts) and screened for their aflatoxins potential in liquid medium and in natural substrates. Out of the10 isolates from sorghums, five isolates produced AFB1 and AFB2 in liquid medium and in sorghums. Out of 16 isolates from peanuts, only 7 isolates were found to produce AFB1 and AFB2 in liquid medium and peanuts.
 Nine isolates of Aspergillus parasiticus (5 from sorghums and 4 from peanuts) were isolated and tested for their aflatoxin production in liquid medium (and in sorghums and peanuts). Two isolates (out of 5 isolates from sorghum ) found to produce aflatoxin AFB1, AFB2, AFG1 and AFG2 in liquid medium and in sorghum grains. Out of 4 isolates from peanuts, only one isolate produced aflatoxins B1, B2, G1 and G2in peanuts.Irradiation of inoculated sorghum and peanuts by A.flavus and A.parasiticus, respectively at 2.0 and 4.0 kGy greatly reduced the number of the initial population count. Meanwhile, application of 6.0 kGy almost completely inactivated both A.flavus and A. parasiticus.
 Irradiation of fungal spores caused morphological changes as seen by scanning electron microscope (SEM). It was obvious from the SEM images that the irradiated spores were crushed and exhibited a high degree of hollowness on their surface.
 All irradiation doses used caused a decrease in all aflatoxins and the reduction percentage was proportional with irradiation dose. The highest irradiation dose of 10 kGy decreased total aflatoxin produced by A. flavusand total aflatoxins B+G produced by A. parasiticusby 33.8% and 24.8%, respectively.
 The investigation onthe inhibitory effects of different concentrations of eight essential oils ( star anise, lemon leaves, marjoram, fennel, orange peel, chamomile and sage) and nine plant extracts (Galangal, Purslane, Garden cress, Mustard, Grape, Mulberry, Jew mallow, Marmalade and Barley) on growth of the toxigenic A. flavus and A. parasiticus indicated that star anise and lemon leaves had the highest effective on the inhibition growth of A.flavus and A.parasiticus with inhibition zones (≥ 40 mm), followed by marjoram, fennel and lavender essential oil.Inhibitory effect of orange peel EOs was the weakest.
 The MIC against A. flavus was established to be 0.5, 1.0 and 4.0 μl/ml in the case of star anise, lemon leaves and marjoram, respectively followed by fennel and lavender ( 8.0μl/ml). While the MFC ofstar anise, lemon leaves, marjoram, fennel and lavender against A. flavus were1.0, 2.0, 4.0, 8.0 and 8.0 μl/ml, respectively.The MIC values against A.parasiticus for essential oils ofstar anise,lemon leaves, marjoram, fennel and lavender was 1.0, 2.0, 4.0, 8.0 and 8.0 μL mL- 1, respectively. The MFC values for the above essential oils were (2.0, 4.0, 8.0, 8.0 and 16.0 μL mL- 1), respectively.
 Fungal mycelia of A.flavus and A. parasiticus treated with sublethal concentration of the star anise, lemon leaves, marjoram, fennel and lavender essential oils (EOs) revealed marked morphological alterations in both the whole length of the hyphae and the apical regions as seen by SEM.
 Among all the essential oils used in the present study the star anise and lemon leaves essential oils showed the highest effective in the suppression of aflatoxins formation, and these EOs were more effective in suppression the formation of aflatoxins by A.flavus than A.parasiticus.
 The effect of star anise EO at concentration of 100 μl on the degradation of AFB1 at concentration of 50 ppb was followed by HPLC-MS/MS. The results indicated that star anise EO reduced the concentration of AFB1 by 95.38%.
 combination treatment of sorghum grains and peanut seeds with 0.5μl/g star anise EO in combination with 2.0 kGy resulted in complete destruction of A.flavus cells as its log count was <1 throughout the storage period (8 weeks ) and the same results with combination of peanuts and star anise EO.
 Thirty bacterial isolates were isolated from the biological samples and they were screened for their antagonistic activity against the aflatoxigenic fungi under investigation on CYA. Out of these 30 bacterial isolates, 6 isolates showed an apparent antagonistic effect against the A.flavus and A.parasiticus
 These six bacterial isolates were screened for their ability to degrade AFB1. The results of TLC indicated that only one isolate ( bacterial isolate no.8) had the ability for complete degradation of AFB1, as no fluorescence spot has been seen in the TLcromatogram in comparison with AFB1 standard. The results of HPLC-MS/MS analysis confirmed TLC results, as the concentration of AFB1 used before bacterial treating was 50 ppb and after bacterial treating was 1.73 ppb. This indicates that treating AFB1 with bacterial suspension of bacterial isolate no.8 caused 96.54% degradation.
 The bacterial strain (No.8) that showed efficient results of inhibition against A.flavus and A. parasiticus strains and has the ability to degrade AFB1 was identified by VITEK 2 Systems Version:08 01 to be Staphylococcus lentus.
 The antifungal effects of bacterial suspension of S.lentus at concentration of 10 and 25 mlkg-1on the growth of toxiginc fungi (A.flavus and A. parasiticus) on sorghum and peanuts seedsduring storage at ambient temperature 280C showed that S.lentus can be effectively used to control these fungal growth in these products and subsequent aflatoxin production.