Valorisation of feather and wool for dietary applications and human nutrition: A step towards sustainable food production

Animal by-products offer a promising solution for growing global protein demand. Keratin is one of the most abundant proteins in animal by-products. Dietary keratin is gaining attention as an alternative protein source with potential applications in nutricosmetics, nutraceuticals, prebiotics, and food packaging. Keratin is naturally water-insoluble and indigestible, necessitating harsh extraction techniques that reduce palatability, digestibility, bioavailability, and alter nutritive composition, making it unsuitable for human consumption. Consequently, the dietary use of keratin remains understudied. Emerging technologies claim to produce dietary keratin with improved nutritional quality. Therefore, this review explores keratin sources, safe extraction methods and the nutritive composition of keratin products successfully used for dietary purposes, while consolidating findings of in vitro and in vivo toxicity, digestibility, and bioavailability. The strengths, challenges, limitations of current approaches, and future directions are discussed. Dietary keratins are a nutritive, safe alternative protein best extracted from wool by microwaving or feathers by acid/alkaline hydrolysis.