Valorising feather keratin: antioxidant activity, cytotoxicity and mutagenicity during processing and gastrointestinal digestion

Chicken feathers are an underutilized resource with high potential for bioactive peptide production. In this study, the valorisation of feather keratin through a three-step processing approach, i.e., keratin extraction with L-cysteine, followed by its enzymatic hydrolysis with pepsin, trypsin, chymotrypsin or subtilisin, and finally Maillard reaction with glucose or xylose of resulting hydrolysates was proposed. Representative preparations were subjected to simulated gastrointestinal digestion to evaluate their behaviour under physiological-like conditions. Subtilisin hydrolysate showed the strongest radical scavenging, iron-chelating and reducing activity. Its glycation with xylose yielded a preparation with enhanced radical scavenging and reducing activity, diminished iron chelation pre-digestion but the highest overall antioxidant capacity post-digestion. Neither processing nor digestion compromised the safety of the keratin preparation, as the absence of acute cytotoxicity or mutagenicity indicated. All digests showed high digestibility and retained antioxidant properties. These findings support the potential of feather keratin preparations as antioxidant ingredients in nutraceutical applications.