Preparation and Properties of Ferulic Acid-Loaded Hydrogel Based on Amyloid Fibrils

To improve the loading rate and stability of ferulic acid, ferulic acid-loaded hydrogel based on amyloid fibrils, formed by heat treatment of hen egg white lysozyme under acidic conditions, was prepared by self assembly. The effects of amyloid fibril concentration, polyphenol addition, and pH on the loading rate of ferulic acid were investigated to optimize the hydrogel preparation conditions. The structural changes of the protein and the microstructure and gel properties of the hydrogel were explored by infrared (IR) spectroscopy, endogenous fluorescence spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and rheometry, and the effects of polyphenol addition on the structure and properties of the hydrogel were evaluated. Ultra-high performance liquid chromatography (UPLC) was used to test the stability of ferulic acid loaded in the hydrogel under thermal and light conditions. A simulated digestion system was established to investigate the in vitro slow release profile of ferulic acid from the hydrogel network. The results indicated that the optimum preparation conditions that provided maximum ferulic acid loading of 6.99% were determined as 70 g/L, 0.6% and pH 5 for concentration of amylose fibril, addition of ferulic acid and pH, respectively. Moreover, the hydrogel could effectively reduce the degradation of ferulic acid under different thermal and light conditions. Compared with lysozyme, the proportion of α-helix and β-sheet in the amyloid fibril increased and the tertiary structure formed an aggregation precursor state, which was more favorable for binding to polyphenols to form structurally stable hydrogels. The amyloid fibril-based hydrogel loaded with 0.6% ferulic acid had the gelation performance, tightest intermolecular structure, highest storage modulus (1655.5 Pa), and lowest swelling rate (160%), and best slow-release performance in vitro.