Purification, characterization, and dehairing properties of alkaline and thermo-stable keratinase by Penicillium citrinum AUMC 14742

The global accumulation of keratin-rich poultry waste poses significant environmental challenges due to its resistance to degradation. This study presents the first comprehensive optimization, purification, and characterization of an alkaline and thermo-stable keratinase produced by Penicillium citrinum AUMC 14742. The strain was confirmed morphologically and molecularly (ITS; GenBank accession PV069363) and showed strong phylogenetic placement within the P. citrinum clade. Keratinase production by Penicillium citrinum AUMC 14742 was optimized using a Box–Behnken design, which identified temperature, pH, and peptone concentration as the most influential variables. Under the optimized conditions of 26 °C, pH 8.0, and 1.5 g/L peptone, the fungus achieved a maximal keratinase activity of 312.75 U/mL. The enzyme was purified 143-fold with a specific activity of 35,423 U/mg and exhibited a molecular weight of 41.87 kDa. Biochemical characterization revealed strong alkalophilicity (optimum pH 10), thermostability (optimum 55 °C), and broad stability in the presence of metal ions, detergents, inhibitors, and solvents. Enzyme activity was markedly enhanced by Mn²⁺ (199%), Zn²⁺ (103%), Co²⁺ (101%), Tween-80 (315%), DMSO (148%), and especially 2-mercaptoethanol (≈ 1634%), while SDS, H₂O₂, Cu²⁺, and Fe²⁺ produced inhibitory effects. Kinetic analysis yielded a Km of 34 mg/mL and a Vmax of 243.9 µmol/min, indicating high catalytic efficiency toward keratin. Functionally, the crude enzyme achieved complete dehairing of goat skin within 15 h at 30 °C, demonstrating its effectiveness as an eco-friendly alternative to chemical depilation. The strong correspondence between the optimized production conditions and the enzyme’s biochemical properties highlights the robustness of the RSM model and underscores the industrial potential of this alkaline, thermo-stable keratinase.