Effects of Extraction Methods on Structural and Functional Properties of Water-insoluble Dietary Fiber from Polygonatum sibiricum Residue

The effects of different extraction methods on the physical and chemical properties and functional characteristics of insoluble dietary fiber (IDF) from Polygonatum sibiricum residue were investigated. The complex enzyme method (CE), ultrasonic-assisted complex enzyme method (UCE) and enzyme-alkali method (CEA) were used to extract IDF. The composition, physicochemical properties, glucose adsorption capacity, cation exchange capacity and DPPH free radical scavenging capacity of three IDFs were analyzed. Results showed that the yield of ultrasound-assisted compound enzyme method was the highest (84.68%). Three IDFs had a higher purity and mainly consisted of cellulose, hemicellulose, and lignin. The purity of UCE-IDF was up to 82.24%. UCE-IDF had the best water holding capacity (4.74±0.66) g/g, oil holding capacity (3.84±0.29) g/g, binding capacity (3.29±0.09) g/g, the highest total phenol content (7.77±0.07) mg/g, the best cation exchange capacity (0.40±0.003) mmol/g, and the antioxidant capacity. CEA-IDF had the highest swelling capacity (5.33±0.11) mL/g and flavonoid content (1.88±0.03) mg/g. CE-IDF had the best glucose adsorption capacity (19326.67±41.63) μmol/g. Physical and chemical characterization indicated that the structure of UCE-IDF was more irregular and had higher thermal stability. The infrared spectra suggested that the three IDFs had the characteristic absorption peaks of cellulose. The X-ray results revealed that the three IDFs were cellulose I crystal. In summary, there were differences in physical and chemical properties and functional characteristics among the three IDFs. UCE-IDF showed significant advantages in several physical and chemical properties, such as water holding, oil holding thermal stability, and antioxidant activity. CEA-IDF was distinguished by its high flavonoid content and the best swelling power. CE-IDF had the best glucose adsorption capacity. The results of this study could provide a theoretical basis for the application of IDF in food processing industry.