3.4 Bioconversion of Waste to Useful Products by Immobilized Enzymes

39

other organic materials. Liquid effluents from agri- and food processing industries

will contain various vegetable-processed water, whey from the manufacturing of

cheese, starch and sugars from bakeries, beverage units and soda industries, fat

materials from yogurt processing units and oil mills, and so on [3]. Immobilization

of enzymes increases the yield of products where it helps to reduce the cost and

efforts. Biotechnology is facilitating the production of many of the chemicals

by environmental-friendly and energy-effective ways. Several chemical methods

which are used in the synthesis of various products are energy-exhaustive and can

cause environmental issues like polluted effluent, high-temperature discharge,

etc. Numerous compounds such as citric acid, amino acids, vinegar, etc., can be

manufactured using waste food stocks. Food protein shortage can be addressed by

the bioconversion of the fruit waste into single-cell protein. For example, the bio-

conversion of single-cell protein from pineapple can be considered as a promising

method for the waste utilization. Single-cell protein can be obtained from cheap

agro-waste materials [12].

Bioconversion of waste to wealthy products was achieved using immobilized

enzymes, and some of these processes are discussed under utilization of protein,

carbohydrate, polysaccharide, and lipid wastes.

3.4.1

Utilization of Protein Wastes

Several varieties of protein-rich wastes from food industries such as oilseeds, dairy,

soybean, and poultry can be converted into valuable chemicals (e.g. polymer precur-

sor) using proteolytic enzymes. Dairy waste products, mainly whey protein, can be

hydrolyzed by immobilized trypsin. Glutaraldehyde-activated agarose maintaining

aspartic protease was shown to hydrolyze whey protein concentrates into antioxi-

dant peptides [13]. In addition to enhanced thermostability at 40–50 ^∘C, the immobi-

lized enzyme also offered a significant reusability, which preserves more than 50% of

the original activity after 10 repeated cycles. The α-lactalbumin protein shows higher

affinity to the immobilized enzyme compared to β-lactoglobulin in the hydrolysis

reaction. It indicates that the immobilization can change the cleavage affinity and

selectivity of biocatalyst [13].

Alcalase alkaline protease was immobilized on chitosan-coated magnetic

nanoparticles using glutaraldehyde as cross-linking agent. The immobilized

enzyme was used for soy protein hydrolysis [14]. The immobilized enzyme showed

the enhanced activity and better thermostability compared to the free enzyme.

Immobilized enzyme retained about 86% of its initial catalytic activity after 10

continuous reaction batches suggesting it as a favorable candidate for the soy

protein hydrolysis [14].

3.4.2

Carbohydrates as Feedstock

Food processing wastes are mainly rich in carbohydrates and can be readily made

vulnerable to the enzymatic valorization by amylases, isomerases, and hydrolases.

Carbohydrates can be mainly converted into simple sugars. Carbohydrates are