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3 Immobilized Enzymes for Bioconversion of Waste to Wealth

demonstrated to be leading carbon sources in many processes. They play a major

role in the microbial metabolisms which will yield abundant fermentative products

like lactose, oil, hydrogen, bioethanol, etc. [15].

Carbohydrates containing crude fibers and free sugars can be converted into

different varieties of products. Free sugars illustrate the naturally occurring

monosaccharaides which are found in honey, fruit extracts, and fruit waste streams,

etc. The enzyme immobilization can be utilized and adapted for the conversion

of carbohydrate into value-added compounds. Industrial food wastes are highly

concentrated with numerous polysaccharides like starch, cellulose, hemicellulose,

pectin, etc. Immobilized cells of Aspergillus awamori and S. cerevisiae produced

amylase and simultaneously caused the hydrolysis of cassava starch and production

of ethanol in the alternating liquid–air phase culture system [16].

Titania–lignin hybrid material was used as a novel support for immobilizing

α-amylase, and immobilized enzyme showed improved thermal and chemical

resistance [17]. Magnetic beads immobilized with α-amylase were used for fishing

amylase inhibitors from the extract of Ginkgo biloba [18]. Same beads can be used

for recovering the inhibitors from agri- and food wastes. Catalytic activity and

stability of α-amylase were improved by immobilizing the enzyme on bioactive

phosphosilicate glass, lignin from bamboo shoot shells, and so on. Immobilized

amylases can be used to convert waste streams rich in carbohydrates into simple

sugars which can be used for various purposes.

3.4.3

Utilization of Polysaccharides

Polysaccharides are abundantly present in the waste streams from the processing of

fruits and vegetables. Polysaccharides can be considered as an attractive substrate

applicants for the enzymatic transformation. Several enzymes mainly, cellulases,

hemicellulases, pectinases, and xylanses have been shown to have a potential to

convert polysaccharide containing waste into a value-added products like biofuel,

bioplastics, sweeteners, etc. Starch-rich waste streams can be found during the pro-

cessing of potato, corn, rice, sweet potato, and so on. In the case of potato, around

16% of starch is being lost by several processes such as washing and slicing. It can also

be used to produce texture plasticizers and modifiers by lipase-catalyzed acylation

reaction [19].

Pectinase enzyme was immobilized on silylated montmorillonite clay through

covalent bond. This immobilized enzyme showed high resistance to highly acidic

conditions, and it was used for the clarification of pineapple juice [20]. Pectinase

enzyme was immobilized on calcium alginate beads, chitosan magnetic particles,

alginate–graphene oxide composite beads, and so on to improve its stability and

reusability. Pectinase from Aspergillus ibericus was immobilized on the functional-

ized nanoporous-activated carbon, and the stability of the enzyme was improved

[21]. This immobilized enzyme was used for treating citrus processing industrial

wastewater, and it cleared the 94% of pectin [21]. Immobilized cellulase enzyme

on economical carrageenan gel disks was shown to disintegrate the cellulose fibers

into nanofibers which are useful in biomedical and food packaging applications