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

Defined peptides with exclusive molecular functionalities from biomass streams provide an untapped treasure for innovative biogenic specialty chemicals and materials. In this context, feather keratin, a natural structural protein with high L-cysteine content, enables access to polythiol-containing peptides, which can be used as matrix compounds for new materials per se and be specifically modified via their amino and acid moieties. This study describes an innovative two-step approach for tailored feather keratin fragmentation involving selective enzymatic hydrolysis followed by optional chemical reduction. Several proteases were investigated to serve as a benchmark for the decomposition of chicken feather keratin, and we succeeded in the controlled decomposition of chicken feathers using trypsin and other specific proteases, producing polythiol-containing peptide fragments. We were able to implement a green hydrolysis process without the need for any denaturants or reducing agents and achieved yields of soluble protein up to 81% (w/w) and thiol concentrations up to 21 mmol L−1. The obtained hydrolysates were used to produce peptide films, and the scalability of the newly developed hydrolysis process has been demonstrated in 25 L batch reactions.