A sustainable solvent based on lactic acid and l-cysteine for the regeneration of keratin from waste wool
Keratin dissolution is the first step toward reusing protein-rich biomass such as waste wool, hair, and feather. This paper reports an efficient and environmentally friendly method for the complete recycling of waste wool using a mixture of lactic acid and L-cysteine as a new green deep eutectic solvent (DES) for isolation of keratin. The dissolution time for a 90% dissolubility was 3.5 hours at 95 °C where 22 mg of wool was dissolved per 1 g of the DES. Keratin was obtained after dialysis of the DES mixture followed by lyophilization. In comparison with the raw wool, the α-helix content of keratin decreased while its β content increased. The keratin isolation with the proposed DES only requires water, L-cysteine, and lactic acid and does not require conventional chemicals such as urea, sodium sulfite, and sodium hydroxide.