Microbial Keratinolysis: Eco-Friendly Valorisation of Keratinous Waste into Functional Peptides

Keratinous wastes, generated from various industries such as poultry processing, slaughterhouses, and salons, accumulate in the environment due to their slow degradation caused by high disulfide cysteine bonds. Traditional methods of managing these wastes, including incineration, composting, open-air burning, and landfilling, have several disadvantages, such as environmental pollution, release of toxic compounds, and breeding of pathogenic and multidrug-resistant microorganisms. Microbial keratinases, produced by bacteria, fungi, and actinomycetes, offer an eco-friendly alternative for valorizing keratinous waste into valuable peptides and amino acids. The biodegradation of keratinous biomass involves four sequential steps: adhesion, colonization, production of keratinolytic enzymes, and breakdown of the keratin substrate. Optimization of culture conditions, such as pH, temperature, substrate concentration, and metal ions, can enhance keratinase production for industrial applications. Keratinases have multifaceted applications in various sectors, including cosmetics, organic fertilizers, leather treatment, animal feed, detergents, and pharmaceuticals. This review highlights the need to explore keratinolytic strains further and improve keratinase yields to develop sustainable solutions for keratinous waste management and generate value-added products, promoting a circular economy. The techno-economic considerations and current limitations in industrial-scale keratinase production are also discussed, emphasizing the importance of future research in this field.