Browsing by Author "Djambaski P."

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    Immobilization in nanomatrices of humicola lutea mycelium for alpha-galactosidase biosynthesis in Laboratoryair-lift bioreactor
    (2010-05-01) Djambaski P.; Aleksieva P.; Spasova D.; Chernev G.; Nacheva L.
    The sol-gel synthesis of both hybrid nanomatrices containing tetraethylortosilicate (TEOS) as an inorganic precursor and lactic acid, or sepharose as an organic component was made. Crystal as well as surface morphology of the hybrids were investigated using different methods: X-ray diffraction, infrared spectra, BET-analysis and atomic force microscopy (AFM). The obtained nanomatrices were applicated for immobilization of the α-galactosidase producing fungal strain Humicola lutea 120-5. The semicontinuous cultivation was carried out in laboratory air-lift bioreactor. Maximal level of enzyme activity (1050-1130 U/l) that was reached in the third to fourth fermentation cycle using TEOS+40% lactic acid was higher than that obtained in the samples with TEOS+20% sepharose (660-770 U/l). The correlation between enzyme productivity and fungal development in the pore structure of the carriers was examined using scanning electron microscopy observation.
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    Silica hybrid nanocomposites
    (2006-03-01) Chernev G.; Samuneva B.; Djambaski P.; Salvado I.; Fernandes H.
    In this work we present experimental results about the formation, properties and structure of sol - gel silica based biocomposite containing Calcium alginate as an organic compound. Two different types of silicon precursors have been used in the synthesis: Tetramethylortosilicate (TMOS) and ethyltrimethoxysilane (ETMS). The samples have been prepared at room temperature. The hybrids have been synthesized by replacing different quantitis of the inorganic precursor with alginate. The structure of the obtained hybrid materials has been studied by XRD, IR Spectroscopy, EDS, BET and AFM. The results proved that all samples are amorphous possessing a surface area from 70 to 290 m2/g. It has also been established by FT IR spectra that the hybrids containing TMOS display Van der Walls and Hydrogen bonding or electrostatic interactions between the organic and inorganic components. Strong chemical bonds between the inorganic and organic components in the samples with ETMS are present. A self-organized nanostructure has been observed by AFM. In the obtained hybrids the nanobuilding blocks average in size at about 8-14 nm for the particles. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.
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    Sol-gel nanomaterials with algal heteropolysaccharide for immobilization of microbial cells, producing a-galactosidase and nitrilase
    (2009-01-01) Djambaski P.; Aleksieva P.; Emanuilova E.; Chernev G.; Spasova D.; Nacheva L.; Kabaivanova L.; Salvado I.M.M.; Samuneva B.
    The main purpose of the present work is the sol-gel synthesis and structure of the hybrid nanomaterials as matrices for two types of cells, producing hydrolytic enzymes. The effect of different percent of algal polysaccharide included in them on the hydrolytic activity of fungal and bacterial cells was investigated. The hybrid sol-gel nanomaterials were synthesized from tetraethylortosilicate (TEOS) as a silicon precursor and heteropolysaccharide (AHPS) from the red microalga Dixonella grisea as an organic part. The structure of these matrices was investigated using different methods: FT-IR, XRD, BET-Analysis, EDS, SEM and AFM. The sol-gel hybrids were used for the immobilization of fungal (Humicola lutea) and bacterial (Bacillus sp.) cells, producing α-galactosidase and nitrilase, respectively. It was established the effect of the quantity of the heteropolysaccharide in the matrices on the activity of these hydrolytic enzymes. Using 20% AHPS in the hybrid nanomaterials the α-galactosidase yield exceeded over two-fold the enzyme titre of the free cells in the third cycle of repeated batch shake flask cultivation. These results correlated with a dense growth of immobilized mycelium observed with scanning electron microscopy (SEM). The increase of the percentage of organic part in the sol-gel matrix up to 20% led to an increase in the nitrilase activity. The addition of 40% AHPS did not significantly affect the decrease of the nitrile biodegradation. © 2009 Taylor and Francis Group, LLC.