Optimization of Different Extraction Processes and Comparative Analysis of Physicochemical Properties of Dietary Fiber from Husk of <italic>Xanthoceras sorbifolium</italic>

The single-factor experiments were combined with response surface methodology to optimize the extraction process of dietary fiber from husk of Xanthoceras sorbifolium, so as to achieve high-value utilization of woody oil processing by-products. Furthermore, the structural and functional properties of soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) extracted through ultrasound-assisted alkaline (Alk) and enzymatic (E) methods were systematically compared. The results indicated that the optimal parameters for the ultrasound-assisted alkaline method were set as follows: Ultrasound temperature 61 ℃, ultrasound time 16 min, ultrasound power 210 W, and NaOH concentration 4.5%. For the ultrasound-assisted enzymatic method, the optimal conditions were determined as enzyme addition 7.9%, ultrasound temperature 55 ℃, ultrasound power 210 W, pH6.7, and ultrasound time 30 min. Under these optimal conditions, the yields followed the order: E-IDF (63.71%±0.16%)>Alk-IDF (59.61%±0.16%)>Alk-SDF (13.17%±0.13%)>E-SDF (11.39%±0.14%). As revealed by scanning electron microscopy, E-SDF exhibited a typically loose and porous structure, while distinct wrinkles were observed on the surfaces of the other components. As confirmed by spectroscopic analyses, all four components possessed characteristic functional groups of dietary fiber. As demonstrated by functional property studies, Alk-IDF showed superior water-holding capacity (12.16±0.05 g/g) and oil-holding capacity (19.12±0.06 g/g), while E-SDF displayed the highest swelling capacity (4.98±0.10 mL/g). At a concentration of 1 mg/mL, the reducing power (0.45±0.01) of E-SDF was higher than that of other components, whereas the free radical scavenging capacity (48.21%±1.02%) of Alk-SDF was the strongest. Overall, husk of Xanthoceras sorbifolium dietary fiber possesses favorable physicochemical properties, which could provide a theoretical basis for its high-value utilization.