Yazar "Smirnova, Irina" seçeneğine göre listele

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    Cascade processing of wheat bran through a biorefinery approach
    (Pergamon-Elsevier Science Ltd, 2014) Celiktas, Melih Soner; Kirsch, Christian; Smirnova, Irina
    Structural characteristics of wheat bran such as surface area, crystallinity, cellulose, hemicellulose, and lignin content significantly affect the yield of biorefinery products such as protein, fermentable sugar and lignin. The aim of the study was to use a sequence of high pressure extraction and hydrolysis processes in a cascade to create high potential value added products, namely, proteins, fermentable sugars and lignin. In the present study, four different sets of experiments were carried out step by step in a cascade sequence. The main experiments were the sequential extraction and hydrolysis which were optimized using design of experiments. Protein extraction from wheat bran was performed in a fixed bed reactor and was maximized to 1.976 g/L at the elicited optimum conditions which were 80 degrees C, pH 9.3 for a duration of 30 min. In the sequential experiment, process parameters such as temperature, flow rate and duration were optimized for liquid hot water (LHW) hydrolysis. The maximum reducing sugar concentration was 200 g/kg which corresponded to 34% per dry biomass obtained at a flow rate of 5 ml/min, temperature of 210 degrees C during a 45 mm treatment. The following step was enzymatic hydrolysis to saccharify the cellulose under high pressure, where the independent variables were pressure, temperature and process time in order to ascertain the process conditions maximizing the reducing sugar content, where a positive correlation was observed between the solid-liquid loading ratio and reducing sugar yield. In the final step, the lignin content of all analyzed lignin fraction was found 70% (w/w). (C) 2014 Elsevier Ltd. All rights reserved.
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    An enzyme immobilized microreactor for continuous-flow biocatalysis of ginsenoside Rb1
    (Wiley, 2021) Kazan, Aslihan; Hu, Xihua; Stahl, Alina; Frerichs, Heike; Smirnova, Irina; Yesil-Celiktas, Ozlem
    BACKGROUND Ginsenoside Rb1 is one of the major bioactive components of Panax ginseng C.A. Meyer (Araliaceae), a medicinal plant that has been used for therapeutic purposes for thousands of years in Asian countries. The pharmaceutical activity of ginsenoside Rb1 highly depends on molecular structure and its deglycosylated metabolites are known to be more potent bioactive compounds. However, these deglycosylated ginsenosides do not exist naturally so they are usually obtained by poorly selective methods, like chemical hydrolysis. RESULTS In this study, the development and characterization of an alginate-based immobilized enzyme microreactor for the catalytic conversion of ginsenoside Rb1 to more bioactive metabolites have been reported. Enzyme kinetic parameters were calculated and characterization tests (such as determination of surface area of alginate matrix, long-term use, and effect of residence time on conversion yield) were conducted. The system was operated under continuous-flow conditions and compared with acidic and batch enzymatic hydrolysis experiments, as conventional approaches. The enzymatic microreactor showed an enhanced activity by producing 13-fold higher amount of ginsenoside F2 than batch enzymatic hydrolysis. CONCLUSION Obtained results indicated that the newly developed enzymatic microreactor could successfully convert ginsenoside Rb1 to more active metabolites and have a potential for the biocatalysis of multiple ginsenosides, as well as pharmaceutically active compounds. (c) 2021 Society of Chemical Industry (SCI).
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    Formulation of organic and inorganic hydrogel matrices for immobilization of beta-glucosidase in microfluidic platform
    (Wiley, 2017) Kazan, Aslihan; Heymuth, Marcel; Karabulut, Dilan; Akay, Seref; Yildiz-Ozturk, Ece; Onbas, Rabia; Muderrisoglu, Cahit; Sargin, Sayit; Heils, Rene; Smirnova, Irina; Yesil-Celiktas, Ozlem
    The aim of this study was to formulate silica and alginate hydrogels for immobilization of beta-glucosidase. For this purpose, enzyme kinetics in hydrogels were determined, activity of immobilized enzymes was compared with that of free enzyme, and structures of silica and alginate hydrogels were characterized in terms of surface area and pore size. The addition of polyethylene oxide improved the mechanical strength of the silica gels and 68% of the initial activity of the enzyme was preserved after immobilizing into tetraethyl orthosilicate-polyethylene oxide matrix where the relative activity in alginate beads was 87%. The immobilized beta-glucosidase was loaded into glass-silicon-glass microreactors and catalysis of 4-nitrophenyl beta-D-glucopyranoside was carried out at various retention times (5, 10, and 15 min) to compare the performance of silica and alginate hydrogels as immobilization matrices. The results indicated that alginate hydrogels exhibited slightly better properties than silica, which can be utilized for biocatalysis in microfluidic platforms.
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    An injectable alginate-based hydrogel for microfluidic applications
    (Elsevier Sci Ltd, 2017) Akay, Seref; Heils, Rene; Trieu, Hoc Khiem; Smirnova, Irina; Yesil-Celiktas, Ozlem
    The objective of this study was to develop an injectable alginate based formulation for immobilizing enzymes into microfluidic systems. The gelation was induced upon lowering the pH by addition of D-glucono-delta-lactone (GDL) and release of Ca+ ions from solid CaCO3. The effects of GDL concentration on enzymatic activity and gelation time were investigated. The results indicated that increasing the GDL concentration increased both surface area and enzymatic activity. Also, chitosan was added to the formulation at different ratios to enhance the stability of enzyme during immobilization. For microfluidic application, 100 mu l spiral coil single channel microchip was fabricated and alginate GDL mixture containing beta-glucosidase was injected to the microchannel prior to gelation. Enzymatic conversion was performed by pumping substrate (pNPG) through the microchannel. The results indicated that the entire substrate was converted continuously during 24 h without any leakage or deactivation of immobilized enzyme. (C) 2017 Elsevier Ltd. All rights reserved.
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    Silica-based monoliths for enzyme catalyzed reactions in microfluidic systems with an emphasis on glucose 6-phosphate dehydrogenase and cellulase
    (Elsevier Science Sa, 2013) Yesil-Celiktas, Ozlem; Cumana, Sucre; Smirnova, Irina
    An efficient on-chip enzyme immobilized monolith microreactor for glucose 6-phosphate dehydrogenase and its extension to cellulase catalyzed reactions is reported. The monoliths were fabricated using the sol-gel technique, where two different silica precursors were investigated, tetraethoxysilane (TEOS) and ethylene glycol modified silane (EGMS) by determining the activity and aging of the enzymes in the gels. Subsequently catalytic reactions were conducted in continuous flow microreactors and the performance of the system was evaluated by applying various flow rates (5, 10, 15, 20 mu l/min). The addition of polyethylene oxide (PEO) reduced shrinkage of the gels during a period of 4 days after gel preparation suggesting a strengthened gel skeleton leading to a reduced channeling within the porous structure. In the microfluidic systems, the highest conversion rates achieved were 20.0% and 28.8% at a flow rate of 5 mu l/min with TEOS-PEO and EGMS-PEO gels. Continuous reaction exhibited better yield than batch-wise operation using same volume/enzyme ratios which can be attributed to favorable enzyme substrate affinities. However, increase in the flow rate resulted in reduced conversion rates due to lower residence times. Consequently, the applied technique not only provided shorter preparation times but also sustained the stability of immobilized enzymes. (C) 2013 Elsevier B.V. All rights reserved.