Keratinous and corneous-based products towards circular bioeconomy: A research review

Abstract

Keratins and corneous proteins are key components of biomaterials used in a wide range of applications and are potential substitutes for petrochemical-based products. Horns, hooves, feathers, claws, and similar animal tissues are abundant sources of α-keratin and corneous β-proteins, which are by-products of the food industry. Their close association with the meat industry raises environmental and ethical concerns regarding their disposal. To promote an eco-friendly and circular use of these materials in novel applications, efforts have focused on recovering these residues to develop sustainable, non-animal-related, affordable, and scalable procedures. Here, we review and examine biotechnological methods for extracting and expressing α-keratins and corneous β-proteins in microorganisms. This review highlights consolidated research trends in biomaterials, medical devices, food supplements, and packaging, demonstrating the keratin industry's potential to create innovative value-added products. Additionally, it analyzes the state of the art of related intellectual property and market size to underscore the potential within a circular bioeconomic model.

Keywords: Alpha-keratin; Biotechnology; Corneous beta-protein; Environmentally sustainable technology; Resource recovery.

Graphical abstract

Fig. 1

Two main strategies for α-keratin and corneous β-proteins production: biotechnological and waste-based. Schematic representation of two approaches for α-keratin and corneous β-proteins production, (i) biotechnological approach and (ii) utilisation of wasted corneous and keratinous materials, and subsequent downstream steps to generate products. Ori: origin of replication. AB: antibiotic.

Fig. 2

Schematic representation of α-keratin and corneous β-protein structure levels. The secondary structure assembles in α-helix or a β-sheet, and the structures for the amino acid glycine (gly), serine (ser), leucine (leu), and glutamate (glu) are shown. Ca.: circa.

Fig. 3

Different procedures to obtain α-keratin and corneous β-protein and typical values of their main properties. Extraction procedures from natural sources (chemical hydrolysis and heating, enzymatic and microbial treatments, dissolution in ionic liquids, and microwaving techniques) and chemical-physical properties (young modules, fracture strength, and toughness) are shown. Gpa: gigapascal. Mpa: megapascal. Ca.: circa.

Fig. 4

Market size in the United States between 2020 and 2030 of α-keratins and corneous β-proteins. The economic values for the hydrolysed (dark green and light orange) and other types (light cyan and dark orange) are shown. The millions (M) of United States Dollars (USD) for 2020, 2021, and 2022 correspond to $212 M, $219 M, and $232 M. The estimated values between 2024 and 2030 are illustrated in light (hydrolysed) and dark (other types) orange. The values are reported according to the content shown in Grand View Research: “Keratin Market Size, Share & Trends Analysis Report By Product (Hydrolysed, Others), By Application By Source (Food & Beverages, Pharmaceutical & Healthcare), By Region, And Segment Forecasts, 2022–2030” [168].