Extraction of Soluble Dietary Fiber from Pumpkin Seed Cake and Analysis of Its Structure and Functional Properties

Following the extraction of oil and proteins from pumpkin seeds, substantial quantities of residual seed cake remain, with dietary fiber being one of its principal active components. The residual pumpkin seek cake remaining after oil and protein extraction was utilized as the raw material in this study to minimize resource waste and maximize utilization. Soluble dietary fiber(SDF) was extracted through the combined application of ultrafine grinding and high-temperature cooking with enzymatic assistance. Initially, the optimal duration for ultrafine grinding was determined based on average particle size. The effects of enzymatic hydrolysis time, temperature, and pH on SDF yield were examined to establish the optimal enzymatic hydrolysis conditions. Subsequently, the structure of SDF was analyzed using scanning electron microscopy, ion chromatography, X-ray diffraction, high-performance liquid chromatography, and Fourier-transform infrared spectroscopy. Lastly, the functional characteristics of SDF were evaluated in terms of adsorption capacity, enzyme activity inhibition, and antioxidant properties. The results showed that the optimal extraction conditions for pumpkin seed cake SDF were as follows: Ultrafine grinding time of 10 minutes, enzymatic hydrolysis temperature of 53 ℃, enzymatic hydrolysis time of 58 minutes and enzymatic hydrolysis pH of 4.3. Under these conditions, the yield of SDF reached 13.07%±0.33%. Structurally, pumpkin seed cake SDF exhibited a loose and porous surface with a molecular weight mainly distributed around 11.97 kDa. Its monosaccharide composition included rhamnose, arabinose, galactose, glucose, xylose, and galacturonic acid, demonstrating a cellulose I-type crystalline structure along with characteristic polysaccharide peaks. Functionally, the adsorption capacities for bile salts and cholesterol were determined to be 6.34 and 10.61 mg/g (pH=7), respectively. The IC₅₀ values for inhibiting α-amylase and pancreatic lipase activities were 13.999 and 9.263 mg/mL, respectively, while the DPPH and ABTS⁺ radical scavenging IC₅₀ values were 3.470 and 3.006 mg/mL, respectively. In conclusion, the ultrafine grinding and high-temperature cooking method assisted by enzymatic treatment yields pumpkin seed cake SDF with relatively high extraction efficiency and potential hypoglycemic, hypolipidemic, and antioxidative activities. These findings provide a theoretical basis for the value-added utilization of pumpkin seed cake resources.