Effects of Different Extraction Methods on Physicochemical, Functional Properties, and Structure of Dietary Fiber from Dragon Fruit Peel

To reduce resource waste and enhance the utilization of dragon fruit peel, the study employed acid hydrolysis (A-SDF), enzymatic hydrolysis (E-SDF), and ultrasound-assisted extraction (U-SDF) to isolate soluble dietary fiber (SDF) from red-fleshed dragon fruit peel. The physicochemical, functional, and structural properties of the SDF extracted by these methods were analyzed and compared. The results showed that U-SDF demonstrated the highest water-holding capacity (32.06±0.66 g/g) and oil-holding capacity (5.36±1.54 g/g), while E-SDF exhibited the greatest swelling capacity (29.10±1.34 g/g). In terms of antioxidant activity, A-SDF showed the strongest scavenging ability against DPPH and hydroxyl radicals, whereas E-SDF exhibited the highest ferric-reducing antioxidant power (FRAP). All antioxidant activities displayed a clear dose-dependent pattern. Additionally, U-SDF exhibited the strongest cholesterol-binding capacity in a simulated intestinal environment (20.34 mg/g at pH7.0). Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed that all SDF types retained the cellulose Ⅰ crystalline structure. Scanning electron microscopy (SEM) revealed that U-SDF possessed a larger specific surface area along with finer flake-like structures, which contributed to enhanced adsorption capacity. The results demonstrated that ultrasound-assisted extraction offers a comparatively high SDF yield while significantly enhancing its functional properties, highlighting its potential as an effective approach for producing high-quality SDF from dragon fruit peel for use in food and nutraceutical applications.