Extraction of Keratin from Rabbit Hair by a Deep Eutectic Solvent and Its Characterization

Abstract

Keratin from a variety of sources is one of the most abundant biopolymers. In livestock and textile industries, a large amount of rabbit hair waste is produced every year, and therefore it is of great significance to extract keratin from waste rabbit hair in terms of the treatment and utilization of wastes. In this study, a novel, eco-friendly and benign choline chloride/oxalic acid deep eutectic solvent at a molar ratio of 1:2 was applied to dissolve waste rabbit hair, and after dissolution keratin was separated by dialysis, filtration, and freeze-drying. The dissolution temperature effect was discussed, and the resulting keratin powder was characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, protein electrophoresis, thermogravimetry and differential scanning calorimetry, and amino acid analysis. During the dissolution process, the α-helix structure of rabbit hair was deconstructed, and the disulfide bond linkages were broken. The solubility of rabbit hair was significantly enhanced by increasing dissolution temperature, and reached 88% at 120 °C. The keratin produced by dissolving at 120 °C displayed flaky powders after freeze-drying, and had a molecular weight ranging from 3.8 to 5.8 kDa with a high proportion of serine, glutamic acid, cysteine, leucine, and arginine. Such features of molecular weight and amino acid distribution provide more choices for the diverse applications of keratin materials.

Keratin Associations with Synthetic, Biosynthetic and Natural Polymers: An Extensive Review

“…% at 120 • C for 2 h, reaching 88 wt.-% solubility of the initial mass. The keratin produced presented a molecular weight ranging from 3.8 to 5.8 kDa and with clear disulfide bonds cleavage and α-helix structure disruption [72].…”

Ionic Liquids and Deep Eutectic Solvents and Their Use for Dissolving Animal Hair

“…Assuming (based on data [18]) that the solubility of the rabbit hair at loading 20 mg/5 g DES-3 is ~89%, create the calibration graph which determines the linear relationship between the solubility of hair (%) and intensity of absorbance of investigated solution at wavelength of 277 nm.…”

Research progress on resource utilization of leather solid waste

“…Keratin is a group of insoluble and fibrous proteins produced in certain epithelial cells of vertebrates, such as hair, wool, feathers, nails, horns, whale baleen and turtle scutes [11]. Compared with other fibrous proteins, keratin has high sulfur content, high structural and strong resistance to chemical attacks [12]. Based on that, it is a challenge to dissolve, extract and apply of keratin.…”

“…Similar to IL, deep eutectic solvent (DES) is a class of the complexation of hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD) with low freezing point, which has also been applied to extraction keratin from hairs and leathers. Wang et al [12] used the mixture of choline chloride and oxalic acid at a molar ratio of 1:2 as DES for extraction keratin from rabbit hair, followed by dialysis, filtration and freeze-drying. The deconstruction of α-helix structure of rabbit hair and the broken of disulfide bond linkages occured during the dissolution and extraction procedure.…”

“…The results indicated that the dissolution of rabbit hair significantly enhanced with the increasing of temperature and reached 88% at 120°C. The keratin displayed flaky powders after freeze-drying, which had a molecular weight in the range of 3.8~5.8 kDa with high proportion (59.8 wt%) of serine, glutamic acid, cysteine, leucine and arginine [12]. However, for these mentioned reagents, the extraction procedure needed to precisely control the solution temperature and the waste hair also needed to be cut into small pieces.…”