Whey protein active films with lemon by-product extract effectively delay lipid oxidation in fresh salmon

Lipid oxidation is a major challenge in the preservation of high-fat foods, limiting shelf life and quality. The use of food industry by-products as natural antioxidants represents a sustainable alternative to synthetic additives. This study aimed to develop whey protein-based active film incorporating lemon by-product extract to delay the lipid oxidation in fresh salmon. Films were produced using whey protein concentrate (WPC) with 0, 1, 2 and 4% ( w/v ) lemon by-product extract and whey protein hydrolysate with lemon flavor (WPH-L). The incorporation of lemon extract significantly increase phenolic content, reaching up to 9.7 mg GAE/dm² and 347 µg/dm² of flavanones (eriocitrin and hesperidin) in WPC-4. Water vapor permeability ranged from 6.22 × 10⁻¹⁰ to 1.28 × 10⁻⁹ g·m⁻¹·s⁻¹·Pa⁻¹, with 2% extract incorporation showing the most balanced barrier performance. Mechanical properties were generally preserved across formulations. All active films significantly reduced lipid oxidation in salmon compared to the control, with WPC-2 and WPH-L achieving approximately 76% reduction in malondialdehyde values after 10 days during refrigerated storage. Notably, WPH-L films exhibited stable mechanical behavior and antioxidant performance without additional extract, highlighting the role of protein hydrolysis. This work provides a comparison between WPC and WPH and identifies optimal extract concentrations for balancing antioxidant performance and film properties. These findings demonstrate that lemon by-product extract incorporated in whey protein–based films represent a promising and practical solution for preserving high-lipid foods by effectively delaying lipid oxidation, while supporting sustainable and circular food packaging strategies.