Extraction of keratin from keratinous wastes: current status and future directions

This review aims to trace the developments of keratin extraction techniques over the last 70 years and possibilities for future research. Keratin is a fibrous structural protein naturally present in the appendages of animals such as hair, wool, feathers, hooves and hides. Currently millions of tons of these appendages are discarded as waste products by the meat, poultry, textile and leather industries. These keratin-rich wastes lack environmental-friendly disposal methods, and are often dumped in landfills or incinerated. Over the last few years, several studies have developed various methods to repurpose these wastes as a potential source for obtaining keratin. Keratin has recently been demonstrated to have applications within the biomedical field (as a scaffold material in tissue engineering, for drug delivery and wound healing), cosmetic products and environmental remediation. To meet the demand for keratin in the above-mentioned applications, research on extracting keratin from different natural sources including keratinous wastes and improving the extraction efficiency thereof is imperative. Hence, with a brief introduction to the structure and occurrence of keratin, the present review extensively focuses on current methods of its extraction from hair, feathers, wool, hides and hooves. Also, the review identifies gaps in current research and outlines future directions in this field.