title: Chemical modification with phthalic anhydride and chitosan: Viable options for the stabilization of raw starch digesting amylase from Aspergillus carbonarius.
abstract: The raw starch digesting type of amylase (RSDA) presents greater opportunities for process efficiency at cheaper cost and shorter time compared to regular amylases. Chemical modification is a simple and rapid method toward their stabilization for a wider application. RSDA from Aspergillus carbonarius was modified with either phthalic anhydride (PA) or chitosan. Activity retention was 87.3% for PA-modified and 80.9% for chitosan-modified RSDA. Optimum pH shifted from 5 to 7 after PA-modification. Optimum temperature changed from 30°C (native) to 30-40°C and 60°C for PA-modified and chitosan-modified, respectively. Activation energy (kJmol-1) for hydrolysis was 13.5, 12.7, and 10.2 while the activation energy for thermal denaturation was 32.8, 80.3, 81.9 for free, PA-modified and chitosan-modified, respectively. The specificity constants (Vmax/Km) were 73.2 for PA-modified, 63.1 for chitosan-modified and 77.1 for native RSDA. The half-life (h) of the RSDA at 80°C was increased from 6.1 to 25.7 for the PA-modified and 138.6 for the chitosan derivative. Modification also led to increase in D value, activation enthalpy and Gibbs free energy of enzyme deactivation. Fluorescence spectra showed that center of spectral mass decreased for the PA-modified RSDA but increased for chitosan modified RSDA.
authors.affiliation: Department of Microbiology, Faculty of Biological Sciences, University of Nigeria, Nsukka, Nigeria. Electronic address: tochukwu.nwagu@unn.edu.ng.
authors.forename: Tochukwu Nwamaka
authors.initials: TN
authors.lastname: Nwagu
authors.affiliation: Department of Microbiology, Faculty of Biological Sciences, University of Nigeria, Nsukka, Nigeria.
authors.forename: Bartholomew
authors.initials: B
authors.lastname: Okolo
authors.affiliation: Life Sciences and Bioengineering, Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Aoyagi
authors.affiliation: Life Sciences and Bioengineering, Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Yoshida
mesh_terms: D000681:Amylases / Q000737:chemistry* / Q000378:metabolism*; D001230:Aspergillus / Q000201:enzymology*; D055162:Biocatalysis; D048271:Chitosan / Q000737:chemistry* / Q000494:pharmacology*; D004063:Digestion; D004795:Enzyme Stability / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D010796:Phthalic Anhydrides / Q000737:chemistry*; D011198:Solanum tuberosum / Q000737:chemistry; D013213:Starch / Q000378:metabolism*; D013696:Temperature
chemical_list: D010796:Phthalic Anhydrides; D013213:Starch; D048271:Chitosan; D000681:Amylases; C043103:phthalic anhydride
keywords: Acylation; Amination; Chitosan; Phthalic anhydride; Raw starch digesting amylase; Stabilization