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Authors: Amin, Faiza
Keywords: Natural Sciences
Chemistry & allied sciences
Issue Date: 2014
Abstract: Pectinases, also known as pectolytic or pectic enzymes, belong to the family of polysaccharidases that contribute to the breakdown of pectins from a variety of plants. Due to versatility in types and reactions catalyzed by these pectin degrading enzymes they have been the focus of research from many decades. The day by day growing demand of pectinases to be employed at commercial level has rendered the research of finding novel pectinases with improved activities and their modification for higher thermal and operational stabilities with affordable costs. In the first step of the present study, cultural conditions were optimized for enhanced production of exo-PG by Penicillium notatum and Cariolus versicolor. Different agricultural wastes were used as substrates for their potential to be used for the production of exo-PG under solid state fermentation conditions. Among these, the wheat bran was proved to be the best substrate for production of exo-PG under solid state fermentation conditions. Under optimized conditions the enzyme activity was observed to be 113 U/gds and 100 U/gds using Penicillium notatum and Cariolus versicolor respectively. Penicillium notatum provided higher activities of exo-PG so it was selected for further production optimization studies under RSM approach which resulted in 131% improvement in activity of exo-PG. Penicillium notatum exo-PG was purified to homogeneity by 3 step purification strategy to achieve 3.05 fold purified enzyme with 2.5% recovery and a specific activity of 27.79 U/mg. 2 different isoforms of exo-PG were detected during column purification with molecular weight of one isoform 20 kDa while other showed 85kDa after SDS-PAGE. Exo-PGI was optimally active at pH 6.0 and 50 °C. The Michaelis-Menten constants km and Vmax of exo-PGI from Penicillium notatum for pectin hydrolysis at optimum temperature were 16.6 mg/mL and 20 mol/mL min-1 respectively. The Penicillium notatum exo-PGI was stable in the broad acidic pH range, with maximum stability in the range of 4.5-6.0. The enzyme followed biphasic deactivation kinetics. Phase-I of the exo-PGI showed a half-life of 6.83 min and 2.39 min at 55 and 80 °C respectively and phase-II of the enzyme showed a half-life of 63.57 min. and 22.72 minutes at 55 and 80 °C respectively. The activation energy for denaturation was 51.66kJ/mole and 44.06kJ/mole for the phase-I and phase-II of the exo-PGI respectively. The enzyme activity was enhanced significantly by Mn2+. Exposure to hydrophobic environment (urea solution) decreased the enzyme activity. Then the Penicillium notatum exo-PGI was immobilized by carrier bound techniques of immobilization on sodium alginate support in order to improve the thermal stability characteristics. Covalent immobilization was more efficient in terms of high relative activity and immobilization efficiency as compared to adsorption immobilization on Na- alginate. Both the immobilization techniques greatly enhanced the thermal stability of enzyme. Temperature optima for exo-PGI activity shifted to higher temperatures as compared to free enzyme. The reusability of immobilized enzyme was very good in both cases of immobilization. Finally the application potential of this exo-PGI from Penicillium notatum was checked by treating various fruit juices. Exo-PGI treatments resulted in significant clarification of fruit juices as evaluated by turbidity, viscosity and absorbance (660nm) measurements.
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