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.

Extracellular amylase production of a thermotolerant Fusarium sp: isolated from Eastern Nigerian soil

In this work, an α- amylase producing Fusarium sp. was isolated from the soil at 50 0C. Growth and enzyme production occurred at 30, 45 and 55 ºC. Soybean meal at 1 percent concentration, supplemented with 0.2 percent NH4Cl and 2.5 percent corn starch elicited the highest amylase yield. Optimum pH for the enzyme was pH 6.5 which retained over 60 percent of its activity after 24 h incubation at the pH range of 4.5-7.0. The enzyme showed high activity from 40-70 0C with optimal activity at 50 ºC and 78 percent activity was retained after incubation at 70 ºC for 30min. Catalytic function of the crude amylase was stimulated by Mg (136 percent), Ca (118 percent) and Zn (118 percent) at 2mM concentrations. The enzyme hydrolyzed cassava, potato and yam starches effectively.