Enhanced keratin extraction from wool waste using a deep eutectic solvent

Abstract

In this study, the solubilisation of waste coarse wool as a precursory step for the large scale valorisation of keratin was investigated using a green deep eutectic solvent (DES) based on L-cysteine and lactic acid. The investigation was undertaken via the response surface methodology and based on the Box-Behnken design for four process variables of temperature (70-110 C), dissolution time (2-10 h), the mass of L-cysteine (0.5-2.5 g) in 20 mL of lactic acid, and wool load in the DES (0.2-0.6 g). The effect of variations in temperature was established to be the most significant process variable influencing keratin yield from waste coarse wool in the current work. An optimum keratin yield (93.77 wt.%) was obtained at the temperature of 105 C, 8 h dissolution time, with 1.6 g L-cysteine in 20 mL of lactic acid using 0.5 g of wool. This study suggests L-cysteine and lactic acid as a green solvent with the potential to scale up keratin recovery from waste wool without significant destruction in the structure of the recovered keratin.

Wool keratin as a novel alternative protein: A comprehensive review of extraction, purification, nutrition, safety, and food applications

“…DES is also renewable, reusable, biodegradable and easily adaptable in industrial processing due to low vapor pressure, flammability, and high dissolution ability (Ozel & Elibol, 2021). Recently investigated applications of DES in keratin production include lactic acid and l ‐cysteine (Okoro et al., 2022; Shavandi et al., 2021), ChCl‐oxalic acid (Wang & Tang, 2018), ChCl‐urea (Jiang et al., 2018), l ‐cysteine‐urea (Wang, Li, et al., 2016) and l ‐cysteine, hydrochloride and sodium sulfite (ethanol‐water mixed system; He et al., 2020).…”

“…The lactic acid and l ‐cysteine DES (2 g l ‐cysteine and 20 ml L(+)‐lactic acid as a solution in water) can dissolve 90% of wool within 3.5 h at 95°C by mixing 22 mg of wool in 1 g of the solvent. However, prolonged time (8 h) and higher temperatures (105°C) might be required to dissolve a similar proportion of wool at a lower l ‐cysteine ratio in DES (1.6 g l ‐cysteine in 20 ml of lactic acid using 0.5 g of wool; Okoro et al., 2022). The mechanism of action in lactic acid/ l ‐cysteine keratin degradation was suggested as the initial degradation of hydrogen bonds by lactic acid, followed by l ‐cysteine cleavage of disulfide bonds (Okoro et al., 2022).…”

“…Thus, the microbial/enzymatic process can address the challenges associated with harsh conditions and toxic chemicals in keratin extraction. However, the enzyme production cycles and durations required to hydrolyze the wool are long, posing a scale‐up challenge (Okoro et al., 2022).…”

“…Some optimum conditions used to solubilize wool and extract keratin reveal a wide range of extraction catalysts. However, some chemicals are considered toxic and nonfit for human consumption (Okoro et al., 2022). Keratin is a novel protein and has not been widely targeted for human consumption as food.…”

“…The use of harsh and potentially toxic chemicals in keratin extraction could limit the application of the material (Yamauchi et al., 1996). Adopting mild processing and safe procedures, for example, microwave‐extraction using food‐grade chemicals (e.g., citric acid and ascorbic acid, Dias et al., 2022), DES ( l ‐cysteine‐lactic acid; Okoro et al., 2022) or enzymatic methods (Gaidau et al., 2019) can support the adaptation of keratin.…”