Add time:07/30/2019         Source:sciencedirect.com

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 (kJ mol−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.

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