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

Abstract

BACKGROUND: Chicken 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.RESULTS: In 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 ∼mol TE g protein −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.CONCLUSIONS: Based 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.

A green process for the specific decomposition of chicken feather keratin into polythiol building blocks

“…The autoclaving conditions are close to hydrothermal treatment, which has been described for keratin decomposition. 68–70…”

“…The autoclaving conditions are close to hydrothermal treatment, which has been described for keratin decomposition. [68][69][70] 3.3 Characterisation of tryptic feather keratin hydrolysates 3.3.1 Conrmation of disuldes via Raman spectroscopy. We recorded Raman spectra of a chicken feather, KHPs, and KHPs aer reduction with TCEP to verify the presence of thiols and disuldes.…”

Sustainable Valorization of Coffee Silverskin: Extraction of Phenolic Compounds and Proteins for Enzymatic Production of Bioactive Peptides

“…To enhance the biological activities of proteins, the extracted proteins need to be hydrolyzed by enzymatic hydrolysis using various types of proteases. For instance, enzymatic hydrolysis of keratin waste by a keratinase from Thermoactinomyces vulgaris TK1-21 resulted in keratin hydrolysate with increased DPPH and ABTS values [10]. In addition, bioactivity of sericin extract [11] and CS protein [12] were increased after proteolytic hydrolysis by alkaline protease from B. halodurans SE5 and Alcalase, respectively.…”