Abstract
One of the agro-industry’s side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering these facts, the keratin-rich waste can be considered as a treasure for the producers interested in the valorization of such slowly-biodegradable by-products. As keratin is a protein that needs harsh conditions for its degradation, and that in most of the cases its constitutive amino acids are destroyed, we review new extraction methods that are eco-friendly and cost-effective. The chemical and enzymatic extractions of keratin are compared and the optimization of the extraction conditions at the lab scale is considered. In this study, there are also considered the potential applications of the extracted keratin as well as the reuse of the by-products obtained during the extraction processes.
Highlights
Faculty of Food Engineering, Tourism and Environmental Protection, “Aurel Vlaicu” University of Arad, Bioresource Department, National Institute for Research & Development in Chemistry and Petrochemistry-ICECHIM Bucharest, 202 Splaiul Independentei, 6th District, 060021 Bucharest, Romania; Abstract: One of the agro-industry’s side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization
Considering the effect on the native structure of keratin extraction methods can be grouped in protected solubilization and unprotected solubilization [64,65]; About the used extraction methods there are chemical, physical, and biological methods [66]; Regarding the effect on the environment, some green methods have been developed, such as microwave irradiation, supercritical water extraction, and steam explosion
KRFM becomes costly if is treated as a waste, but valorization of these by-products through the eco-friendly extraction methods of the keratin might turn it into a valuable resource for the obtaining of new materials of great importance in different industries
Summary
The structural units of keratin are 20 amino acids, united by varied inter and intramolecular links consisting of hydrogen, disulfide, hydrophobic, and ionic bonds, leading to increased mechanical strength and stability of keratin structure and keratinous materials [1,26,27,28]. The formation of β-keratin filament implies four lateral β-strands, constituted because of polypeptide chain folding in its central region, which links through intermolecular hydrogen bonds [7,41] and produces small rigid planar surfaces lightly bent together in the form of a pleated arrangement [3]. Such proteins are rich in sulfur amino acids and possess lower molecular mass (from 10 to 15 kDa) compared to the other types of keratins [38] Their function is to cross-link the keratin intermediate filaments (KIFs) and are involved in the interaction of KIFs with the cytoskeleton and cellular membranes [42]. Γ-keratin is less susceptible to protease hydrolysis [44]. γ-keratin promotes cell rescue after thermal injury in vitro and is more suitable for the preparation of wound dressing products [45]
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