Abstract: Soluble dietary fiber (SDF) was extracted from Sargassum hemiphyllum fermented with Aspergillus niger or Aspergillus oryzae in order to investigate the effect of fungal fermentation on the yield, structural improvement, functional properties and antioxidant activity of SDF from S. hemiphyllum. The results showed that SDF prepared by fermentation with the two strains had advantages over each other. Compared with the untreated control group, A. oryzae fermentation increased the yield of SDF by 3.625 times, and the obtained SDF, which was bright in color and loose in structure, had higher purity and lower molecular mass (6.3 kDa), and consequently higher water-holding capacity (WHC) and sodium cholate adsorption capacity. A. niger fermentation increased the yield of SDF by 3.375 times, and the molecular mass of the obtained SDF was 39.4 kDa, which had a porous structure and significantly improved water-holding capacity, cholesterol and sodium cholate adsorption capacity. In vitro antioxidant experiments showed that fermentation improved the hydroxyl radical scavenging capacity of SDF, and decreased its scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical and oxygen radical. In summary, this study can provide a reference for the preparation of SDF by fungal fermentation and its development and application in functional foods.

Key words: soluble dietary fiber; fermentation method; Aspergillus oryzae; Aspergillus niger; Scagassum hemiphyllum