الفهرس 
Introduction
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Abstract
Pullulan is a polysaccharide polymer consisting of maltotriose units, it’s produced from starch by the polymorphic micromycete Aureobasidium pullulans. Pullulan polymer is very important with a wide range of applications in food, agricultural, pharmaceutical and chemical industries. The present study was limited with respect to achieve the broad objectives of furthering the knowledge of pullulan producing A. pullulan strains, gaining information concerning factors influencing the formation of pullulan and studying some properties of pullulan polymer. The results obtained are summarized in the followings: Three strains of the fungus A. pullulans were obtained from MIRCEN, Ain Shams Univ., Cairo. The isolates were morphologically examined to confirm their purity. The strains were cultured in both static and shaked cultures for pullulan production. All the test fungal strains showed an ability to produce the biopolymer pullulan. Generally, shaked cultures produced high amounts of pullulan in comparison with static cultures. The strain A. pullulans ATCC 42023 recorded the highest pullulan accumulation, followed by strain A. pullulans ATCC 12535. The strain A. pullulans ATCC 16628 showed feeble pullulan production in spite of its good characteristics. The production of pullulan by the test strains was highly dependent on the carbon source on which they were cultivated. Sucrose promoted the highest pullulan (10.4 g/l) for A. pullulans ATCC 12535. As regard strain, A. pullulans ATCC 42023, glucose syrup promoted the highest pullulan productivity (24.18 g/l). No correlation was reported between biomass increase and pullulan production. Molasses, sugar cane molasses or sugar beet molasses, and their treatment methods affected pullulan production. EDTA treated sugar beet molasses promoted the higher pullulan production (14.83 g/l) for A. pullulans ATCC 12535. However, growing of A. pullulans ATCC 42023 on treated molasses resulted in pullulan production smaller than those produced during growth on glucose syrup. As regards nitrogen sources, it was found that urea + yeast extract allowed the highest production of pullulan with A. pullulans ATCC 12535, while yeast extract alone appeared as being the most favorable nitrogen source for A. pullulans ATCC 42023. Considering the phosphate source, it was found that Na3PO4.12H2O allowed the highest production of the polymer pullulan with A. pullulans ATCC 12535, while Na2HPO4 appeared as being the most favorable phosphate source for A. pullulans ATCC 42023. The majority of phosphorus sources were not favorable for the two test strains. Regarding the influence of initial reaction of culture media employed for pullulan production, it was found that a pH 5.5 seemed to be optimal for pullulan accumulations by the two test strains. Considering the inoculum size, it was found that 5% and 10% inoculum size allowed the highest production of pullulan with A. pullulans ATCC 12535 and A. pullulans ATCC 42023 strains, respectively. Conversion coefficient (%) at 5% inoculum size reached 61.39% for A. pullulans ATCC 12535 and at 10% inoculum size reached 73.67% for A. pullulans ATCC 42023. Pullulan yield % at (5%) inoculum size reached 49.30% for A. pullulans ATCC 12535 and at 10% inoculum size reached 66.70% for A. pullulans ATCC 42023. Some properties of pullulan produced from the fungal strain A. pullulans ATCC 42023 were studied. It was found that pullulan produced has greenish colour, soluble in water at 25C, the pH for solution soluble in water (from 5-7), maximum ash 2% and melting point over 300C. IR was studied for pullulan.