Abstract
In this paper glucoamylase from Aspergillus niger was immobilized by using a modified version of cross-linked enzyme aggregates (CLEA). The co-aggregates were cross-linked with glutaraldehyde; meanwhile dextrin and xanthan gum as protecting agents were added, which provides high affinity with the enzyme molecules. The immobilized glucoamylase was stable over a broad range of pH (3.0–8.0) and temperature (55–75 °C); dependence shows more catalytic activity than a free enzyme. The thermostability, kinetic behavior, and first-order inactivation rate constant (ki) were investigated. The two types of protector made the immobilized glucoamylase more robust than the free form. Both of the immobilized enzymes have excellent recyclability, retaining over 45% of the relative activity after 24 runs. In addition, immobilized enzymes reduced only 40% of the initial activity after three months by the storability measure, indicating high activity.
Highlights
The industrial preparation of glucose involves a preliminary starch saccharification to maltodextrin that uses α-amylase, and a second hydrolysis to glucose that uses glucoamylase [1,2].Glucoamylase (1,4-α-glucanglucohydrolase, EC 3.2.1.3) is an enzyme preparation that decomposes starch into glucose by tearing-off glucose units from the non-reduced end of the polysaccharide chain
Dextrin and xanthan gum as protecting agents were added in the process of prepared cross-linked enzyme aggregates (CLEA) of glucoamylase, and we focus on the characteristics of modified CLEA and free glucoamylase
Glutaraldehyde is a reagent mostly used for cross-linking protein molecules [8,24]; it induces changes in protein catalytic activities through penetrating the internal structure of the protein and reacting with amino residues
Summary
The industrial preparation of glucose involves a preliminary starch saccharification to maltodextrin that uses α-amylase, and a second hydrolysis to glucose that uses glucoamylase [1,2]. The stability of an immobilized enzyme is dictated by many factors such as the number of bonds formed between the enzyme and carrier [10]. There are disadvantages to the use of direct cross-linking of untreated enzyme molecules such as poor mechanical performance, small granules, and low enzymatic activity By contrast, pre-treatment of enzymes by physical or chemical precipitation or adding protectants makes them more robust for the same cost. Xanthan gum is a nature polysaccharide and an important industrial biopolymer [22] It has been used in a wide variety of enzyme modifications for a number of important reasons, such as emulsion stability, temperature stability, and pseudoplastic rheological properties [23]. The storage stability and tolerance of immobilized enzymes were enhanced significantly with xanthan gum in previous studies. We examined immobilized and native glucoamylase with respect to kinetic parameters, recoverability, and performance in different conditions
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