Green Processing of Lignocellulosic and Food Waste in Biorefinery and Circular Bioeconomy: The Role of (Bio)Catalysts

Dear Colleagues,

Wastes from the agro industry and food production, including those made from fruit, vegetables, meat, and poultry, are produced in vast quantities. In most cases, landfilling and incineration are used to remove this material. However, there is currently a shortage of land for waste disposal, and burning waste results in air pollution, particularly the emission of particulate matter PM2.5, which causes health issues and lowers quality of life. To achieve the aims of the circular economy and the biorefinery with zero waste generation, strategies to turn waste into products with increasing value and the green waste management approach are therefore required.

Agro-industrial and food wastes are often composed of organic materials such as proteins and carbohydrates. These wastes appear in the form of leaves, straw, husks, stovers, and peels, while wastes from meat and poultry are represented by a nails, horns, and feathers. Enzymatic hydrolysis has become a central principle of biomass degradation since it is essential for waste conversion to degrade high-molecular-weight biomasses into smaller molecules or the building blocks for microbial fermentation.

The major enzymes for the breakdown of carbohydrates and proteins, respectively, are known as carbohydrate-active enzymes (such as cellulase, xylanase, amylase, mannanase, and pectinase) and proteolytic enzymes (such as protease and keratinase). In the biorefinery industry, cellulases are employed to break down cellulose into glucose, which is then fermented by microorganisms to produce biochemicals and biofuels such as bioethanol and butanol. In contrast, xylanases can be used to produce xylooligosaccharides and can be combined with cellulases to enhance the hydrolysis of cellulose in biomass. Cassava pulp is treated with amylases in order to recover the sugar. Mannanases and pectinases, on the other hand, can be employed to treat fruit peel in order to extract soluble polysaccharides and phytochemicals. Proteases and keratinases can break down protein-rich plant materials such as mung bean hulls and chicken feathers, respectively, to produce a protein hydrolysate, antimicrobial peptides, and amino acids. Additionally, lignin has become recognized as a source of antioxidants and antibacterial agents. Lignin is a component of lignocellulosic material and is generally regarded as a waste in the cellulose-based industry. In order to produce antioxidant and antimicrobial lignins, ligninolytic enzymes such as laccase and lignin peroxidase are crucial.

In fact, employing enzymes has a number of benefits over physicochemical methods for turning biomass into high-value marketable products, including excellent selectivity and purity of the final product, mild conditions, and low energy input. However, there are drawbacks to employing enzymes on a large scale, such as their high cost, poor yields, instability, and reusability. The development of an effective protein expression system with proper protein folding and glycosylation is therefore the current direction of enzyme research, along with searching for new, robust microorganisms. Additionally, in order to lessen environmental concerns and low-toxic discharges, substantial research is being carried out son the development of physicochemical processes using deep eutectic solvents and water as green catalysts or solvents.

This Special Issue focuses on utilizing biotechnologically relevant enzymes or catalysts for processing agro-industry and food wastes, including fruit, vegetable, meat, and poultry, to value-added products with the potential for commercialization.

We welcome the submission of research articles, reviews, and perspectives related, but not limited to, the following themes of interest:

• Application of carbohydrate-active enzymes and proteolytic enzymes in agriculture, food, feed, and the biofuel/chemical industry
• Production of biofertilizer, bio-composting, and biocontrol agents using hydrolytic enzymes and microbes
• Effects of pretreatment methods on biomass structure and enzymatic activity
• Production of a protein hydrolysate, antioxidant and antimicrobial peptides, and amino acids
• Production of antioxidants and antimicrobial lignin
• Development of enzymatic processes or physicochemical processes using green catalysts or solvents for polysaccharide and protein extraction
• Enzymology of carbohydrate-active enzymes, proteolytic enzymes (e.g., protease and keratinase), and lipases
• Development of protein expression and hosts for expressing enzymes, as well as techniques for increasing enzymatic activity and stability
• Modular structures and substrate–enzyme interactions
• Computational tools for designing enzymes

Dr. Paripok Phitsuwan
Dr. Ken-Lin Chang
Guest Editors

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