Orange Peel Valorization Through Citric Acid Extraction: Linking Process Conditions to Structural and Functional Properties of Pectin

Citrus processing generates large amounts of peel residues rich in pectic polysaccharides that can be valorized through eco-friendly extraction methods. This study evaluated how citric acid extraction conditions (pH 1.46-2.64, 51-96 °C, 20-70 min) influence the yield, composition, and functional properties of pectin obtained from orange peel. A central composite design (CCD) assessed the effects of pH, temperature, and time on pectin yield, degree of esterification (DE), and galacturonic acid (GalA) content. Pectin obtained under conditions maximizing each response was further characterized by structural, thermal, rheological, and functional properties. The maximum values obtained were 26.5% yield (96 °C, 70 min, pH 1.46), 84.1% GalA (74 °C, 42 min, pH 2.17), and 67.0% DE (50 °C, 70 min, pH 1.46). High yield was favored by high temperature and low pH, whereas GalA was maximized under moderate conditions, although at low recovery (5.6%). GalA-optimized pectin showed higher gel hardness (641 g) and apparent viscosity (0.64 Pa·s) than yield-optimized pectin (122 g; 0.28 Pa·s). This study demonstrates that optimizing for yield, GalA, or DE produces structurally distinct pectin fractions with different functional properties rather than a single optimal extraction condition.