Characterization of glucoamylase adsorption to raw starch |
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Authors: | Bipin K Dalmia and Zivko L Nikolov |
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Institution: | a Department of Chemical Engineering, Iowa State University, Ames, IA, USA b Department of Food Science and Human Nutrition, Iowa State University, Ames, IA, USA |
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Abstract: | The adsorption of Aspergillus niger glucoamylase forms (GA-I and GA-II) to raw corn starch was studied as a function of pH, ionic strength, and temperature. A three-parameter model was developed to account for the specific and nonspecific adsorption of GA-I to starch. The adsorption of the GA-II form to raw starch was weak and independent of the pH and ionic strength of the mixture. GA-I was bound strongly to the starch surface, with association constant values ranging from 2 to 5 × 106 M?1. Maximum adsorption capacities (saturation concentrations) Qmax for GA-I were affected by pH, inonic strength, and temperature and varied between 1.6 and 4.3 mg protein g?1 starch. The tightly bound GA-I could be specifically eluted from the starch surface with maltose, maltodextrin, or soluble starch. The adsorption of GA-II to starch in the presence of acarbose (glucoamylase activity inhibitor) indicated that the active site participates minimally in the adsorption process. The comparison of the distribution coefficients of GA-I and GA-II showed that the starch-binding domain, present only in GA-I, increases the affinity of GA-I for starch by two orders of magnitude. |
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Keywords: | Aspergillus niger glucoamylase starch-binding domain adsorption elution pH ionic strength |
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