Efficient isolation of keratin from protein-rich waste biomass: a practical approach to minimize environmental impact and valorize waste biomass

Abstract

Among various protein-containing biomass wastes, waste animal wool, poultry feather, and human hair are considered one of the most important renewable sources of keratin. Animal wool and human hair are utilized for the production of several products. However, the substantial quantity of short fibers that are inappropriate for spinning and being unusable is thrown away as waste resulting in significant environmental issues in terms of their accumulation in water bodies resulting in obstruction of waterways and other related problems. Similarly, poultry wastes, especially waste chicken feathers (WCF) are dumped or burnt or used as low-value fertilizer in certain applications. The purpose of this research is to develop an efficient method that can extract the recoverable keratin from various wastes and effectively utilize the spent solvent in the extraction process. Herein suitability of an aqueous solution of quaternary ammonium hydroxide known as tetramethyl ammonium hydroxide (TMAOH, 25% w/w in water) to solubilize these protein wastes and extract keratin from them was investigated. The solvent could solubilize ca. 39–44% w/w of waste animal wool (WAW), 19–25% of waste human hair (WHH), and 55–60% of WCF. Crude keratin with ca. 19–20%, 35–37%, and 69–74% were isolated from WAW, WHH, and WCF, respectively. The chemical and structural stability of keratin thus isolated was established. The recovered TMAOH, insoluble WAW, and WCF were found to be nontoxic to soil microbes. The recovered TMAOH thus generated after isolation of keratin was used for green gram (Vigna radiata) seed treatment, and a substantial increase in the height (4–12%) and weight (9–58%) of the plants was observed. Treating biomass waste as a source of high-value compounds may minimize environmental impact by reducing the waste load.