Effect of Ultrasound Treatment on the Structural and Techno-Functional Properties of Feather-Derived Keratin

Chicken feathers, an underutilized poultry-processing by-product, are a rich keratin source whose native disulfide-crosslinked structure limits solubility and functional applicability. This study investigated the effects of probe ultrasound treatment (30–60% amplitude, 10 min) on the structural and techno-functional properties of alkali-extracted chicken feather keratin (CFK) to support its valorization in various applications. Control (untreated) and ultrasound-treated CFK samples were characterized by FTIR, SDS–PAGE, free sulfhydryl (–SH) content, ζ-potential, surface hydrophobicity, antioxidant activity (ABTS and CUPRAC assays), in vitro protein digestibility, water solubility, oil-holding capacity, and emulsifying and foaming properties. FTIR and SDS–PAGE revealed that the characteristic amide bands and apparent molecular-weight profile of keratin were mainly preserved following ultrasound treatment, whereas Amide I deconvolution indicated an amplitude-dependent reduction in native β-sheet content and Ellman’s assay showed a loss of free –SH groups. Ultrasound treatment enhanced several functional properties in an amplitude-dependent manner. Surface hydrophobicity, oil-holding capacity, emulsifying activity, and ABTS-based antioxidant activity showed the highest values at 40% amplitude, while water solubility and emulsion stability were highest at 60%. The in vitro digestibility remained above 90% for all samples. These findings show that ultrasound treatment can modify the functional performance of feather keratin in an amplitude-dependent manner without marked changes in its apparent molecular-weight profile or its major amide bands, supporting its potential as a functional ingredient for various applications.