Effects of Ultrasound-Assisted Combined Enzymatic Modification on Physicochemical and Functional Properties of Dietary Fiber from Pitaya Peel

To enhance the high-value utilization of pitaya processing by-products, pitaya peel was used as the raw material to optimize the preparation process of dietary fiber modified by ultrasound-assisted combined enzymatic modification using response surface methodology. The effects of modification on the nutritional and bioactive components, structural characteristics, physicochemical properties, and functional properties of pitaya peel powder were systematically analyzed. The results showed that the optimal conditions were determined as follows: cellulase addition of 2.5%, xylanase addition of 2.0%, ultrasonic time of 43 min, and ultrasonic power of 300 W. The mass ratios of protein, lipid, and ash in the modified powder exhibited no significant changes, while the mass ratios of cellulose, hemicellulose, and lignin decreased significantly (P<0.05). The mass fraction of soluble dietary fiber (SDF) increased markedly from (10.67±0.31) g/100 g to (26.63±0.13) g/100 g, and the total dietary fiber content reached (72.41±0.07) g/100 g. The modification led to partial loss of some bioactive components, with the contents of flavonoids, betacyanins, and total phenolics decreasing by 22.22%, 14.37%, and 5.73%, respectively. The ultrasound-assisted combined enzymatic modification significantly improved the water-holding capacity [(5.75±0.06) g/g], oil-holding capacity [(3.30±0.12) g/g], swelling capacity [(15.33±0.76) mL/g], and solubility (51.00%±0.31%) of the pitaya peel powder (P<0.05). Structural characterization revealed that the modified dietary fiber acquired a loose and porous morphology, with enhanced thermal stability, while the main structure of the dietary fiber remained intact. Furthermore, the modified dietary fiber showed significantly increased glucose adsorption capacity, α-amylase inhibitory activity, and sodium cholate and cholesterol adsorption capacities (P<0.05). In conclusion, the ultrasound-assisted combined enzymatic modification synergistically enhanced the physicochemical and functional properties of dietary fiber from pitaya peel, providing a theoretical basis for its high-value application in functional foods.