Impact of Osmotic Dehydration on the Physicochemical Properties and Bioactive Compounds of Ecuadorian Valencia Orange (Citrus sinensis) Peels

Large volumes of orange residues generated by domestic and industrial consumption in Ecuador are commonly discarded, contributing to environmental burdens despite their high content of bioactive antioxidant compounds. This study evaluated the impact of osmotic dehydration (OD) on the physicochemical properties and functional attributes of Ecuadorian Valencia orange (Citrus sinensis) peels. A 23 factorial design was applied, evaluating blanching time (BT: 5–10 min), sucrose concentration (SC: 50–70 °Brix), and immersion time (IT: 12–24 h). Results revealed highly significant (p < 0.01) non-linear effects of processing variables on mass transfer kinetics. Notably, milder intermediate conditions (50 °Brix, 12 h, 5 min BT) yielded significantly lower water activity (0.70 ± 0.005) and moisture content (11.83% ± 0.12%) compared to severe processing (70 °Brix, 24 h, 5 min BT), which trapped internal water (aw = 0.81 ± 0.009, moisture = 13.77% ± 0.20%), which suggested the occurrence of solute-induced surface case hardening, minimizing subsequent moisture diffusion. Processing induced an extraordinary reduction in total phenolic content (TPC) by 86% to 93% (p < 0.01) from the fresh baseline down to a range of 1.40–2.70 mg GAE/g dw, alongside a critical drop in antioxidant capacity, with post-dehydration ABTS retained at <65% and FRAP at <30% of fresh values due to cellular membrane disruption and subsequent hydrophilic leaching. Conversely, lipophilic total carotenoid content was maximized under severe configurations (10 min BT, 70 °Brix SC, 24 h IT) at 52.92 ± 2.19 µg/g dw (p < 0.01) due to protective sugar matrix encapsulation. Ultimately, these findings demonstrate that while osmotic processing involves an inherent trade-off in soluble antioxidant depletion, it establishes a precise technological process window to stabilize highly perishable citrus by-products into microstructurally stable, value-added dietary fiber matrices, providing a predictable and scalable upcycling strategy for functional ingredient development within the regional circular bioeconomy.