Comparison of degradation abilities of α- and β-amylases on raw starch granules

The degradation abilities of α-amylase from Bacillus amyloliquefaciens and β-amylases from Bacillus cereus and soybean on raw starch granules from various botanical sources (potato, sweet potato, wheat, rice and corn) were examined by scanning electron microscopy. All the amylases showed different degradation patterns on starch granules. The α-amylase was more efficient than the β-amylases. α-Amylase showed both centrifugal and centripetal hydrolysis on corn, rice and wheat granules, but only centrifugal hydrolysis on potato granules. On the other hand, β-amylase moved very slowly on granules. The kinetic assays which explain the release of maltose were carried out at 12, 18 and 24 h. The rice granules were found to be the best substrate for enzymic hydrolysis by α and β-amylases. In addition, While Bacillus cereus β-amylase hydrolyzed corn granules efficiently at 45°C; soybean β-amylase was 60% less active than bacterial β-amylase at the same temperature. [1]


Recent Advances in Microbial Raw Starch Degrading Enzymes

Raw starch degrading enzymes (RSDE) refer to enzymes that can directly degrade raw starch granules below the gelatinization temperature of starch. These promising enzymes can significantly reduce energy and simplify the process in starch industry. RSDE are ubiquitous and produced by plants, animals, and microorganisms. However, microbial sources are the most preferred one for large-scale production. During the past few decades, RSDE have been studied extensively. This paper reviews the recent development in the production, purification, properties, and application of microbial RSDE. This is the first review on microbial RSDE to date. [2]


Production of raw starch digesting amylase by Aspergillus niger grown on native starch sources

Aspergillus niger isolated from rotting cassava produced raw starch degrading amylase on cassava, maize, sorghum and soluble potato-derived starch as the sole carbon source without prior gelatinisation. Maximum activity of the amylase was attaired using cassava starch as substrate. The crude enzyme solution which comprised a mixture of raw and non raw starch digesting amylase degraded both cereal and tuber or root starches significantly. Source of assay starch significantly influenced raw starch digesting activity. Optimum pH for the raw starch degrading and the extracellular amylase were 6.0 and 3.5-4.0, respectively. However, both enzyme activities appeared to be uninfluenced across a relatively broad pH range 3.0-7.0. No correlation was found between the capacity of starch to induce expression of the enzyme and its susceptibility to enzyme digestion. The adsorbability of the various starches to raw starch digesting amylase was directly related to their digestibility. [3]


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 non-catalytic 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.[4]


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.[5]
Reference

[1] Sarikaya, E., Higasa, T., Adachi, M. and Mikami, B., 2000. Comparison of degradation abilities of α-and β-amylases on raw starch granules. Process Biochemistry, 35(7), pp.711-715.

[2] Sun, H., Zhao, P., Ge, X., Xia, Y., Hao, Z., Liu, J. and Peng, M., 2010. Recent advances in microbial raw starch degrading enzymes. Applied biochemistry and biotechnology, 160(4), pp.988-1003.

[3] Okolo, B.N., Ezeogu, L.I. and Mba, C.N., 1995. Production of raw starch digesting amylase by Aspergillus niger grown on native starch sources. Journal of the Science of Food and Agriculture, 69(1), pp.109-115.

[4] Nwagu, T.N., Aoyagi, H. and Okolo, B.N., 2012. Adsorption and Stabilization of a Raw Starch Digesting Amylase on Micro Bead Silica Gel 300 A. Biotechnology Journal International, pp.85-101.

[5] Amadi, O.C. and Okolo, B.N., 2013. Induced; Thermal Influence on Morphology of Aspergillus carbonarius During Raw Starch Digesting Amylase Production. Microbiology Research Journal International, pp.355-367.