Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 363

alginate-coated chitin supports [80]. To prepare the support for enzyme immobilization,
chitin was coated with sodium alginate through amide linkages. Although different syn-
thetic methods for conjugating polymers to enzymes have been described, in general these
procedures only involve the coupling to reactive groups from the polypeptide chains of
enzymes. Since the sugar residues in glycoenzymes are often not required for their activi-
ties, a novel and better approach for stabilizing these biomolecules would be the conjuga-
tion of polymers to activated carbohydrate moieties of glycoenzymes. The authors deal with
the stabilization of invertase by coupling of chitosan to periodate-oxidized sugar moieties
from this enzyme [81].
The yield of immobilized protein was determined as 85% and the enzyme retained 97%
of the initial chitosan-invertase activity. The immobilized enzyme was stable against incu-
bation in high-ionic-strength solutions and was fourfold more resistant to thermal treat-
ment at 65°C than the native counterpart. The biocatalyst prepared retained 80% of the
original catalytic activity after 50 h under the continuous operational regime in a packed-
bed reactor [80].
8.5 Chitosan Composite for Enzyme Immobilization
Chitosan composites are divided into four groups: chitosan-biopolymer mixture prepared
by mixture; chitosan-tethered membrane; chitosan-based PECs; and chitosan-inorganic
composites. Inorganic materials involve magnetic particles, metal oxide (except for iron
oxide), metal nanoparticles, silica, CNTs, clay, and inorganic salt.
8.5.1 Chitosan-biopolymer Mixture Prepared by Mixture
The simplest method of preparing composites was by direct mixture of chitosan and other
materials, which can change the gel structure, mechanical properties, and immobilization
conditions.
Several glycosidases (βG, Ara, Rha), purified from an A. niger enzyme preparation, were
immoblized simultaneously with a method because of their possible application in the
wine-making and fruit-juice-processing industries. Immobilization of the three enzymes
was carried out by inclusion using chitosan gels and subsequent cross-linking with GA.
This was followed by the addition of various agents to improve the gel's physical and
mechanical properties, reduce enzyme release phenomena, and increase immobiliza-
tion yields and operational stability. It was shown that the best additives were gelatin and
silica gel [82].
Adriano et al. reported that the use of sodium alginate, gelatin, or κ-carrageenan, activa-
tion with GA, Gly, or ECO, and addition of microorganisms followed by cellular lysis led
to a modification of the gel structure. Different size distributions of pore beads may be
obtained through the covalent or physical interactions of the two polymers. The biopoly-
mers gelatin, alginate, and κ-carrageenan have groups that are negatively charged at neu-
tral pH and can interact with the positively charged amine groups of chitosan, forming
different internal nets. The hydrogen bonds formed between chitosan, alginate, or
κ-carrageenan modify the porosity of the gel. They also change the chitosan molecule
conformation, which becomes more resistant to drastic conditions of pH and temperature.
Another way to modify the gel internal structure is its formation in the presence of a