Sustainable valorization of chicken feather waste via integrated protic ionic liquid and microbial keratinase system

Chicken feathers represent a major agro-industrial waste stream, rich in recalcitrant β -keratin that resists conventional degradation. In this study, we developed a hybrid valorization strategy that integrates green ionic liquids (ILs) with microbial keratinase hydrolysis to efficiently convert feather waste into bioactive amino acids. A protic ionic liquid, monoethanolammonium formate ([MEA][HCOO]), was synthesized and characterized via FTIR and 1 H NMR. Optimization studies demonstrated that waste feathers completely dissolved in [MEA][HCOO] IL at 130 °C within 2 h. The dissolved substrate was subsequently hydrolysed by keratinase produced by Bacillus licheniformis (MTCC 2617), which exhibited peak activity of 12.9 ± 0.3 U mL −1 after 48 h of cultivation at 37 °C and pH 7. The integrated IL–enzyme system significantly enhanced feather hydrolysis, releasing 151.1 μg/mL soluble protein (1.511 mg total), equivalent to 15.1 mg protein g −1 feather, as determined by the Bradford assay. Amino acid analysis further confirmed serine (24.0 mg g −1 feather (2.40 mg per 20 mL batch)) and glycine (8.09 mg g −1 feather (0.809 mg per 20 mL batch)) as dominant products, identified by RP–HPLC and ninhydrin assays, respectively. To maximize amino acid recovery, RSM was employed to optimize dissolution and hydrolysis parameters, identifying pH 8.0 and hydrolysis temperature of 35 °C. This integrated approach demonstrates a sustainable circular bioeconomy pathway, converting low-value poultry waste into high-value biomolecules for applications in agriculture, cosmetics, and biomedicine.