WG4 investigates the bioactive properties of extracted fibers, including antioxidant activity, bound phenolics, prebiotic effects, and interactions with gut microbiota. This research reveals the health-promoting potential of food waste-derived fibers and supports their application in functional foods and nutraceuticals. By understanding bioavailability, bioefficacy, and digestion-related release mechanisms, WG4 provides crucial data for industry innovation, regulatory alignment, and targeted product development in collaboration with WG6 and WG5.