Hydrothermal–enzymatic process for the bio‐valorization of keratin wastes by thermostable keratinase from Thermoactinomyces vulgarisTK1‐21

Abstract

AbstractBACKGROUNDChicken feather (CF), pig bristle (PB), and pig hoof (PH) are substantial keratin wastes from slaughterhouses. They are generated in large quantity, are almost totally unexploited protein resources, and are potential substrates for value‐added products.RESULTSIn this study, Thermoactinomyces vulgaris TK1‐21 showed a good ability to produce keratinases for the degradation of all three keratin wastes within 5 days at pH 8.5 and 45 °C. Maximum keratinase activities of 5.72, 4.21, and 4.89 U mL−1 were obtained for CF, PB, and PH, respectively. T. vulgaris TK1‐21 secreted two types of extracellular enzymes (keratinase_TK1‐21), which were purified and characterized as thermitase (keratinase‐I) and carboxypeptidase T (keratinase‐II) with estimated molecular weights of 28 and 36 kDa, respectively. Dialyzed crude keratinase_TK1‐21 could efficiently hydrolyze the hydrothermally treated CF, PB, and PH into keratin hydrolysate (KH). Soluble protein concentrations of 6.94, 3.87, and 6.32 mg mL−1 were obtained at pH 9.0, 55 °C, and 72 h, which were three times higher than those of untreated substrates. In addition, this hydrothermal–enzymatic method showed high KH productivity (60–70%) with a production cost of 16.24 USD kg−1. The ferric‐reducing antioxidant power assay and radical scavenging activities of KH derived from CF, PB, and PH were 19–42, 2.5–4.9, and 608–1314 μmol TE gprotein−1. Bioplastic starch blended with these KHs showed improved tensile strength (2.55–4.40 MPa) and elongation at break (40–54%) when compared to bioplastics without KH blending.CONCLUSIONSBased on our results, we suggest an alternative valorization approach with techno‐economic feasibility for keratin waste bioconversion into a potential active ingredient for bioplastics via hydrothermal–enzymatic processing. © 2023 Society of Chemical Industry (SCI).