Maize kernels (cv. ‘Jidan 66’) were exposed to different intensities (2.5, 3.5 and 4.5 mT) of low-frequency static magnetic fields for different time periods (12, 24, 36, 48, 60 and 72 h) and germinated at 25 ℃ for 96 h. The changes in the growth indices, the phenolic contents, the hypoglycemic activity of phenolic compounds and the key enzyme activities related to polyphenol metabolism in germinated maize kernels were investigated. The results showed that the sprout length and germination rate of maize seeds treated at magnetic field intensity of 3.5 mT for 60 h were significantly increased, and the contents of bound and free phenols were increased by 72.72% and 47.16%, and the contents of syringic acid and p-coumaric acid were also significantly increased compared to the untreated control (P < 0.05). In addition, the activity of phenylalanine ammonia lyase (PAL), 4-coumaric acid-CoA ligase (4CL), and cinnamate 4-hydroxylase (C4H) were improved under low frequency static magnetic field, and the α-glucosidase and α-amylase inhibitory activity of bound and free phenolics were enhanced. These pieces of evidence indicated that low frequency static magnetic field can promote the growth of maize seeds and the accumulation of phenolic compounds, and improve the hypoglycemic activity of phenolic compounds in germinated maize seeds .

The effect of Armillaria mellea fermentation alone and combined with static magnetic field on the structure and physicochemical properties of zein was explored. Fourier transform infrared (FTIR) spectral analysis showed that static magnetic field treatment changed the secondary structure of the protein during the fermentation process. The analysis of ultraviolet (UV) absorption spectra and intrinsic fluorescence spectra showed that static magnetic field treatment resulted in protein unfolding and group exposure. The results of scanning electron microscopy (SEM) showed that after static magnetic field treatment, the surface of the protein became rougher with obvious pores and increased specific surface area. The results of thermodynamic analysis showed that static magnetic field treatment obviously increased the denaturation temperature of the protein, decreased the particle size, increased the absolute value of the zeta potential, and resulted in increased content of free sulfhydryl groups and decreased content of disulfide bonds. In addition, the physical and chemical properties of the protein were significantly changed by static magnetic field-assisted fermentation. The water and oil retention capacities, emulsification properties, foaming capacity and foam stability were increased significantly, reaching maximum values of 3.86 g/g, 4.22 g/g, 26.83 m²/g, 37.67% and 58.12%, respectively on the 7th day of fermentation. The emulsion stability was decreased significantly, reaching a minimum level of 34.10% on the 7th day. In summary, static magnetic field-assisted fermentation of zein by A. mellea can change its structure of and effectively improve its physical and chemical properties, thereby improving the added value and utilization rate of zein.

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.