Abstract
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.
Highlights
The global growth of meat consumption over the years has contributed to a considerable increase of meat industry waste, including viscera, skins, meat trimmings, bones, blood and epidermal attachments (Meruane and Rojas 2012)
This review highlights biotechnological approaches for the use of microbial keratinolytic enzymes as a way to contribute to the sustainable treatment of keratinous wastes
These are some examples of research works developed in the application of keratinases for hair removal, yet many additional studies can be found in the literature (Table 1)
Summary
The global growth of meat consumption over the years has contributed to a considerable increase of meat industry waste, including viscera, skins, meat trimmings, bones, blood and epidermal attachments (feathers, hair, horns, teeth, nails and claws) (Meruane and Rojas 2012). The specific recalcitrance of keratin is a factor that makes difficult its management and recycling. Conventional methods, such as incineration, and alkaline or acid hydrolysis, used for disposal of this biomass, are high cost and not considered ecologically safe. This leads the meat industry to seek for alternative sustainable technologies to treat these residues (Callegaro et al 2019). Microbial keratinases have emerged as an alternative to the treatment of keratin-rich wastes. This review highlights biotechnological approaches for the use of microbial keratinolytic enzymes as a way to contribute to the sustainable treatment of keratinous wastes. Research works needed to expand the range of promising applications, considering the environmental and economic importance of this subject are discussed
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