Effects of Different Extraction Methods on the Structural and Functional Properties of Soluble Dietary Fibre from Sweet Potatoes

In this study, hot water treatment (WT), ultrasonic treatment (UT), ultrasonic-sodium hydroxide treatment (UST), ultrasonic-enzyme treatment (UET), and ultrasonic-microwave treatment (UMT) were used to treat sweet potatoes. The structural, physicochemical, and functional properties of the extracted soluble dietary fibres (SDFs) were named WT-SDF, UT-SDF, UST-SDF, UET-SDF, and UMT-SDF, respectively. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal properties, and Brunauer-Emmett-Teller (BET) analysis were employed. The structural results indicated that the UST-SDF exhibited the best thermal stability, highest crystallinity, and maximum specific surface area. Moreover, compared to hot water extraction, ultrasonic extraction, or ultrasonic extraction in combination with other methods, enhanced the physicochemical and functional properties of the SDF, including extraction yield, water-holding capacity (WHC), oil-holding capacity (OHC), glucose adsorption capacity (GAC), glucose dialysis retardation index (GDRI), sodium cholate adsorption capacity (SCAC), cholesterol adsorption capacity (CAC), nitrite ion adsorption capacity (NIAC), and antioxidant properties. Specifically, the UST-SDF and UMT-SDF showed better extraction yield, WHC, OHC, GAC, CAC, SCAC, and NIAC values than the other samples. In summary, these results indicate that UST and UMT could be applied as ideal extraction methods for sweet potato SDF and that UST-SDF and UMT-SDF show enormous potential for use in the functional food industry.