Industrial sustainability of microbial keratinases: production and potential applications

Keratinases are proteolytic enzymes with a particular ability to cleave peptide bonds in keratin, and in other proteins. Due to their broad-spectrum of activity, keratinases are considered viable substitutes for chemical and thermal treatments of protein-rich industrial by-products. Among these protein residues, special attention has been given to keratinous materials (feathers, hair, horns, etc.), which disposal through harsh conditions methods, such as acid/alkaline hydrolysis or incineration, is not considered ecologically safe. Microbial keratinolytic enzymes allow for keratin degradation under mild conditions, resulting in keratin hydrolysates containing undamaged amino acids and peptides. In this review article, we offer perspectives on the relevance of these unique biocatalysts and their revolutionary ascent in industries that generate keratin-rich wastes. Additionally, we share insights for applications of keratinases and protein hydrolysates in agriculture, animal feed, cosmetics, phamaceuticals, detergent additives, leather processing, and others. Due to the scientific importance of keratinases and their potential use in green technologies, searching for bacterial and fungal species that efficiently produce these enzymes may contribute to the sustainability of industries.