Structural Characteristics and Physicochemical Properties of Soluble Dietary Fiber Preparations from <i>Citrus sinensis</i> Peel

This study evaluated the effects of acid, alkaline, cellulase-assisted, and xylanase-assisted extraction methods of orange by--products (Citrus sinensis peel) on the chemical composition, structure and physicochemical properties of resulting soluble dietary fiber (SDF) preparations.The highest extraction efficiency was obtained using the method with citric acid (31.37%).The pectin, hemicellulose and cellulose contents of fiber produced with this method (A-SDF) were 58.63, 7.38, and 8.42 g/100 g dry matter (dm), respectively.The method with citric acid resulted in an A-SDF with a water holding capacity of 19.17 g/g and an emulsifying capacity of 91.00%, which were superior to those obtained using alkaline and enzyme-assisted extractions.Fiber obtained by xylanase-assisted extraction had similar emulsion stability (75.77%), water swelling capacity (8.67 mL/g), and oil holding capacity (2.49 g/g) as A-SDF.Scanning electron microscopy images showed that A-SDF had a rough, porous surface favorable for hydration, while alkaline-extracted SDF (B-SDF) displayed dense, compact structures.Fourier-transform infrared spectra confirmed stronger hydroxyl and carboxyl group signals in A-SDF, suggesting its better hydrophilicity.X-ray diffraction analysis indicated the highest crystallinity index in B-SDF (41.83%), whereas fibers extracted using enzymes had more amorphous patterns, reflecting structural disruption.These findings demonstrate that acid-assisted extraction using citric acid is the most effective method for extracting soluble fiber from citrus by-products.