pH Mediated L-cysteine Aqueous Solution for Wool Reduction and Urea-Free Keratin Extraction

Regenerated keratin from waste wool is one of the most critical modern biomaterials due to its intrinsic biodegradability, biocompatibility, and mechanical durability. However, the most common keratin regeneration methods use hazardous reducing reagents and a high dose of chaotropic reagents, leading to high cost and secondary environmental pollution. We used L-cysteine as a reducing reagent to extract wool keratin without using a high amount of urea, high-temperature, and hazardous chemicals compared to the traditional reduction methods. L-cysteine aqueous solutions at pH 11–13.5 can dissolve wool fibers efficiently to regenerate keratin. The extracted keratins were then characterized using infrared spectroscopy, sodium dodecyl sulfate–polyacrylamide gel electrophoresis, and thermogravimetry analysis. At pH 12, L-cysteine aqueous solution dissolved about 67.84% of wool fiber, and the yield of keratin was about 56%. The extracted keratin exhibited characteristic keratins bands with molecular weights of approximately 100 kDa (keratin dimer), 45–65 kDa (type I and II keratins), and 10–38 kDa (keratin associated keratin, KAP), indicating that the keratins retained their structural integrities. Economic analysis revealed that avoidance of the use of 8 M urea in the reduction method significantly decreased the total cost of the extraction method.Graphical Abstract