Highly efficient extraction of large molecular-weight keratin from wool in a water/ethanol co-solvent

Abstract

A large number of wool fiber by-products, short and coarse wool fibers are difficult to spin and are disposed of by the wool industry, creating a burden on the environment. In this study, L-cysteine hydrochloride and sodium sulfite were used as reducing agents to extract keratin from natural wool in an ethanol-water mixed system. The molecular weight of the extracted keratin is up to 130 kDa with a high yield of 67%. It has been proven that the reducing agent destroyed partial disulfide bonds, ethanol destroyed partial hydrogen bonds and hydrophobic interactions, and the α-helix chain was converted into a β-folded chain and random coil after extraction by instrumental analysis using a Fourier transform infrared spectrometer and X-ray diffraction. The recombination of small keratin molecules can be proven by the increase in protein particle size and molecular weight via a particle size analyzer and SDS-PAGE respectively.

Biofunctionalization of Natural Fiber-Reinforced Biocomposites for Biomedical Applications

“…Wool and chicken feathers are mainly composed of keratin, a structural protein similar to SF. The chemical structure of keratin is predominantly an α-helix in chicken feathers [55] and a super coiled polypeptide chain with an α-helix and β-sheet in wool [56]. These structures are tightly packed via cross linkages, hydrogen bonds, Van der Waals and electrostatic interactions.…”

A sustainable solvent based on lactic acid and l-cysteine for the regeneration of keratin from waste wool

“…Besides, the characteristic peak of amide III observed around 1515-1518 cm −1 for the wool and regenerated keratin sample can be attributed to the C-N and C-O stretching vibrations. 6,16,23 Furthermore, the CH, CH 2 , and CH 3 vibration peaks appeared between 2800 and 3000 cm −1 for both wool and keratin. The keratin sample exhibited a characteristic peak around 1049 cm −1 attributed to the symmetric and asymmetric S-O stretching vibrations, indicating the presence of cysteine-S-sulfonated residues in the extracted keratin.…”

“…Highdensity disulfide cross linkages with the highest bond energy have connected different zones of the polypeptide chains of the keratin molecule and along with the hydrophobic interactions and van der Waals forces they endow the keratin with high mechanical strength and structural stability. 8 Various methods for keratin dissolution and extraction have been applied; however, the available processes have shown some shortcomings and disadvantages. 9 Utilization of concentrated strong acids or bases in chemical methods damages the protein structure by dissociation of peptide bonds, consequently decreasing product yields.…”

“…The solvent destabilizes the macromolecular structure by weakening the intermolecular and intramolecular forces, and breaking down the disulfide bonds has the potential to dissolve and extract keratin from wool without damaging the peptide bonds. 6,8 The DES in this study is formed by the combination of L-cysteine (amino acid) and L(+)-lactic acid (2 : 20, w/v). Lactic acid (2-hydroxypropanoic acid) is a carboxylic acid with a pK a value of 3.86 (20°C) and is a natural hydrogen bond donor (HBD).…”

Photocatalytic Properties of a Novel Keratin char-TiO2 Composite Films Made through the Calcination of Wool Keratin Coatings Containing TiO2 Precursors

“…Besides, wool keratin is stabilized by other bonds, including hydrophobic, hydrogen, and ionic bonds [26]. Wool fibers are a kind of natural protein textile material having unique properties, which depend upon its chemical composition and morphological characteristics [27]. The water insolubility, chemical resistance, biodegradability, and good mechanical properties of wool fibers are mainly determined by the disulfide bond of keratin [28].…”