Effect of Edible Fungal Fermentation on Structure and Functional Properties of Ginseng Insoluble Dietary Fiber

Ginseng residue, the by-product of the extraction of bioactive components from ginseng, is rich in dietary fiber. In this study, ginseng insoluble dietary fiber (IDF) was prepared by ginseng residues fermented with Morchella esculenta, Hericium erinaceus or Armillaria mellea in order to explore the effect of fermentation by edible fungi on the structure and functional properties of IDF. The results of scanning electron microscopy (SEM) showed that a large number of honeycomb pores appeared on the fermented fiber surface and the specific surface area increased compared with that before fermentation. The particle size of fermented fiber decreased. Fourier transform infrared (FTIR) spectroscopy showed that fermentation resulted in partial degradation of cellulose, hemicellulose and lignin in IDF. The results of X-ray diffraction showed that the fermented fiber had a higher degree of crystallinity. The results of differential scanning calorimetry (DSC) showed that the fermented fiber had better thermal stability. The results of functional characteristics showed that compared with unfermented IDF, the water-holding capacity, oil-holding capacity and water-swelling capacity of IDF fermented by Armillaria mellea increased by 74.2%, 93.6% and 124.38%, and all of the increases were higher than those in IDF fermented by the other three strains. Additionally, IDF fermented by Armillaria mellea had the highest glucose adsorption capacity (17.91–83.56 mg/g), glucose dialysis retardation index (GDRI, 30.29%–68.27%), cholesterol adsorption capacity (8.44 mg/g at pH 2.0, and 12.35 mg/g at pH 7.0), sodium cholate adsorption capacity (6.57–12.7 mg/g), nitrite adsorption capacity (1642.37 μg/g at pH 2.0, and 1249.13 μg/g at pH 7.0) and cation exchange capacity. In summary, fermentation by edible fungi can effectively improve the functional properties of ginseng insoluble dietary fiber, which will promote its application in foods.