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BACKGROUND Cocoon waste, solid waste from the silk industry, is currently utilized as low‐cost spun silk yarn. In this study, the enzymatic valorization process of yellow cocoon waste to produce antioxidative sericin hydrolysate and fibroin film was demonstrated. RESULTS The enzymatic process involving thermostable alkaline protease from Bacillus halodurans SE5 (protease_SE5) was superior to the conventional high temperature and high pressure and 0.5% Na2CO3 processes. Protease_SE5 produced sericin hydrolysate with high peptide concentration (0.335 mg mL–1) and provided degummed fibroin with a complete structure. Sericin hydrolysate from protease_SE5‐assisted hydrolysis showed remarkable radical scavenging activities on ABTS, DPPH and FRAP assays with 602, 3.90 and 24.8 μmol Trolox equivalents (TE) g−1 protein, respectively. After ultrafiltration and size‐exclusion chromatography, two active fractions (F1 and F2) were obtained from sericin hydrolysate with ABTS radical scavenging activity of 2120 and 3289 μmol TE g−1 protein, respectively. Identification of bioactive peptides by de novo sequencing was conducted, and seven candidate peptides were identified with high content of key antioxidative amino acids (His, Phe, Trp, Tyr and Arg) in the sequences. Moreover, bioactivities of several of the peptides were predicted by bioinformatics databases. Besides, the mechanical properties of enzyme‐derived fibroin film were also improved, with tensile strength and elongation at break of 62.1 MPa and 3.6% in the dry state, and 8.5 MPa and 140% in the wet state. CONCLUSION This enzymatic process could be an effective way for valorizing cocoon waste. The value‐added products from agricultural waste have promising applications in food, pharmaceutical and biomedical materials. © 2020 Society of Chemical Industry (SCI)

Cassava starch was blended with glycerol to prepare thermoplastic starch (TPS). Thermoplastic starch was premixed with sericin (TPSS) by solution mixing and then melt-blended with polyethylene grafted maleic anhydride (PEMAH). The effect of sericin on the mechanical properties, morphology, thermal properties, rheology, and reaction mechanism was investigated. The tensile strength and elongation at break of the TPSS10/PEMAH blend were improved to 12.2 MPa and 100.4%, respectively. The TPS/PEMAH morphology presented polyethylene grafted maleic anhydride particles (2 μm) dispersed in the thermoplastic starch matrix, which decreased in size to approximately 200 nm when 5% sericin was used. The melting temperature of polyethylene grafted maleic anhydride (121 °C) decreased to 111 °C because of the small crystal size of the polyethylene grafted maleic anhydride phase. The viscosity of TPS/PEMAH increased with increasing sericin content because of the chain extension. Fourier-transform infrared spectroscopy confirmed the reaction between the amino groups of sericin and the maleic anhydride groups of polyethylene grafted maleic anhydride. This reaction reduced the interfacial tension between thermoplastic starch and polyethylene grafted maleic anhydride, which improved the compatibility, mechanical properties, and morphology of the blend.

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.

Cassava starch was blended with glycerol to prepare thermoplastic starch (TPS). TPS was premixed with sericin (TPSS) by solution mixing and then melt-blended with polyethylene grafted maleic anhydride (PEMAH). The effect of sericin on the mechanical properties, morphology, thermal properties, rheology, and reaction mechanism was investigated. The tensile strength and elongation at break of the TPSS10/PEMAH blend were improved to 12.2 MPa and 100.4%, respectively. The TPS/PEMAH morphology presented PEMAH particles (2 µm) dispersed in the TPS matrix, which decreased in size to approximately 200 nm when 5% sericin was used. The melting temperature of PEMAH (121°C) decreased to 111°C because of the small crystal size of the PEMAH phase. The viscosity of TPS/PEMAH increased with increasing sericin content because of the chain extension. Fourier-transform infrared spectroscopy (FTIR) confirmed the reaction between the amino groups of sericin and the maleic anhydride groups of PEMAH. This reaction reduced the interfacial tension between TPS and PEMAH, which improved the compatibility, mechanical properties, and morphology of the blend.