Microbial keratinases for feather keratin bioprocessing: Production, properties and industrial applications

The poultry industry has been gaining momentum across the globe and coupled with the increase in poultry production, is the accumulation of poultry waste, mainly feathers. Traditional approaches for managing feather waste, such as landfilling and incineration, adversely affect the environment by exacerbating pollution and ultimately leading to human health issues. Feathers however, are composed of keratin, a valuable source of protein, which can be recycled as a poultry feed ingredient. Various physical and chemical treatments have been employed to recover feather keratin; however, these methods yield a product that is nutritionally inferior and involve harsh processing conditions that adversely affect the environment. To overcome these adversities, an alternate method is explored using keratinolytic microorganisms and their enzymes to degrade keratin. This review is a conscientious literature survey which substantiates the strategy for valorising keratin waste using microbial keratinases, followed by detailed insights into the production, characterisation, and industrial applications of keratinases across various sectors. The primary objective is to examine the mechanism of keratin biodegradation, evaluate different assays for keratinase activity, and develop a strategy for screening keratin-degrading microorganisms. Drawing on an extensive collection of literature, this review provides further insight into the production, purification, and characterisation of keratinases. Furthermore, the application of keratinases, which has a significant beneficial impact in various sectors such as animal feed, detergents, textiles, leather, and others, has been discussed. Thus, this work uniquely positions keratinase-based bioprocessing as a promising solution to environmental challenges while unlocking economic value from feather waste.