Physicochemical properties of keratin extracted from wool by various methods

Abstract

Keratin from wool fibers was extracted with different extraction methods, for example oxidation, reduction, sulfitolysis, and superheated water hydrolysis. Different samples of extracted keratin were characterized by molecular weight determination, FT-IR and NIR spectroscopy, amino acid analysis, and thermal behavior. While using oxidation, reduction, and sulfitolysis, only the cleavage of disulfide bonds takes place; keratin hydrolysis leads to the breaking of peptide bonds with the formation of low molecular weight proteins and peptides. In the FT-IR spectra of keratoses, the formation of cysteic acid appears, as well as the formation of Bunte salts (–S–SO3–) after the cleavage of disulfide bonds by sulfitolysis. The amino acid composition confirms the transformation of amino acid cystine, which is totally converted into cysteic acid following oxidative extraction and almost completely destroyed during superheated water hydrolysis. Thermal behavior shows that keratoses, which are characterized by stronger ionic interaction and higher molecular weight, are the most temperature stable keratin, while hydrolyzed wool shows a poor thermal stability.

Proteins from Agri-Food Industrial Biowastes or Co-Products and Their Applications as Green Materials

“…Keratin comprises a mixture of high-molecular-weight fibrous proteins whose properties are greatly influenced by the methodology (chemical, enzymatic, and ionic solution) employed for its extraction from different epidermal appendages (mainly, feathers and wool, but also nails, claws, beak, hair, or horns) [ 109 ]. The amino acid composition may vary depending on the source as well as on the animal breed or diet [ 110 ], being the cystine content usually high [ 111 , 112 , 113 , 114 ]. Transparent materials have been obtained primarily by casting, resulting in water-sensitive films with adequate UV barrier properties and thermal stability up to 200 °C [ 109 , 114 ].…”

Research progress on resource utilization of leather solid waste

“…Ionic liquid extraction uses ionic liquid with low vapour pressure, high ion conductivity, high thermal stability and nonvolatility to extract keratin, but a part of water soluble amino acids can be lost and the extraction procedure needs to be performed at inert atmosphere requiring expensive specialized equipment. For instance, Rajabinejad et al [25] extracted keratin from wool fibers with different extraction methods, such as, oxidation, reduction, sulfitolysis and superheated water hydrolysis, and the physicochemical properties of these keratin were compared. Although similar extraction yields were obtained, the characterization results showed that the time, cost and environmental sustainability of these methods were different.…”

“…Considering the similar molecular weights, sulfitolysis using sodium metabisulfite as extraction reagents seemed to be the cheapest and least harmful extraction method, comparison with oxidative and reductive extraction using peracetic acid and dithiothreitol as reagents respectively. And low molecular weight of the peptides was obtained by superheated water hydrolysis, which is easy to accomplish on a large scale and a relative cheap and environmentally friendly method [25].…”

The influence of alkaline extraction on some keratin hydrolysates properties

“…The development of techniques for the efficient production of biomass from poultry farming or sheep breeding for keratin extraction should prove to be very useful for the sustainable management of huge waste. Denaturation techniques, such as methods based on reduction (Zeng and Lu, 2014), oxidation (Brown et al, 2016) and enzymatic hydrolysis and ionic liquids (Rajabinejad et al, 2018) are benchmarks for obtaining good yields and soluble keratin (Hearle, 2000).…”