Induced; Thermal Influence on Morphology of Aspergillus carbonarius During Raw Starch Digesting Amylase Production.

Aim: To investigate increased thermal influence on morphology of Aspergillus carbonarius during RSDA production. Place and Duration of Study: Microbial fermentation Unit, Department of Microbiology, Faculty of Biological sciences, University of Nigeria, between July 2009 and August 2010. Methodology: In shake flask cultures thermal influence on A. carbonarius morphology and productivity investigated. Mycelial morphology was characterised by means of image analysis using as parameters, mean diameter, roughness, circularity and compactness of pellet. Thermal effect on amylase activity, total protein, biomass concentration and pH were also investigated. Results: Shifting the temperature from 27ºC to 37ºC significantly affected the morphological parameters of the pellets, but RSDA activity was not altered. The interesting thing about the morphology is the shearing off of the hairy part of the pellet at an increased temperature and subsequent agglomeration. At 27ºC the RSDA activity increased steadily with an optimum activity of 293U/ml at 96h and subsequently decreased to 75U/ml by the end of the fermentation. At 37ºC a maximum activity of 291U/ml was achieved at 72h of fermentation but this decreased to 87U/ml at the end of fermentation. Higher biomass concentration and total protein were obtained at 37ºC. The pH dropped from an initial of 5.0 to 3.0 and 2.5 for 27ºC and 37ºC temperature conditions respectively. Conclusion: Induced thermal increase resulted to changes in pellet morphology but raw starch digesting amylase activity was not altered.

Adsorption and Stabilization of a Raw Starch Digesting Amylase on Micro Bead Silica Gel 300 A.

Aims: To produce a robust starch hydrolyzing enzyme (improved catalytic and noncatalytic properties) by the adsorption of the soluble enzyme on micro bead silica gel. Place and Duration of Study: Department of Life Sciences and Bioengineering, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba-shi Ibaraki-ken, Japan between July 2009 and August 2010. Methodology: Ten types of Micro Bead silica gel with pore sizes ranging from 0.4-100 nm were screened to determine the best support for the immobilization of a microbial raw starch digesting amylase (RSDA). The micro bead which gave the highest yield was selected for further studies. Properties of the immobilized enzyme were compared to the free type to determine the effect of immobilization on catalytic, storage and operational stability. Results: Micro Bead 300 A gave the highest yield and the optimum condition for adsorption of the RSDA was at pH 5, 25°C for 24 h. Optimum pH of the immobilized enzyme shifted from 5 to 4.5 and optimum temperature from 30 to 50°C. The immobilized amylase retained over 70% of its initial activity after 12 h incubation at 70°C in 0.2 M citrate phosphate buffer pH 5 whereas free enzyme lost 92% initial activity under same conditions. Immobilized enzyme retained 95% activity after 10 batch reactions of 30 min each and 100% activity after storage for 6 weeks at room temperature. Conclusion: Immobilized RSDA was marginally more pH and temperature stable compared to the native type. It also exhibited storage stability and could be re-used repeatedly without considerable desorption during washing. The kinetic and stability features combined with the properties of the support make this process appealing for industrial application.