Formation and Structural Characteristics of Heating-Induced Amyloid Fibrils Derived from Rice Albumin at Different pH Values

The comparison of rice albumin (RA) after heat treatment at neutral and acidic conditions was investigated in this study. Compared to the decreased thioflavin T (ThT) intensity of RA at pH 2 during heating, the ThT intensity of RA at pH 7 increased throughout the process of fibrillization. After fibrillization, the ThT intensity of RA at pH 7 was significantly increased by 27%, 38% and 35% at the protein concentrations of 1%, 2% and 4%, respectively. In addition, worm-like fibrils with a contour length of 100-300 nm were formed after heating at neutral conditions, accompanied by an increased average particle size and structural re-arrangement. Furthermore, the fibril formation at pH 7 involved the enhancement of an ordered β-sheet structure. However, only spherical agglomerate with a larger average particle size (>2000 nm) was observed when RA was heated at pH 2, because excessive hydrolysis destroyed the fibril-core sequences of RA. Additionally, the low solubility and high hydrophobicity of RA at pH 2 were not conducive to the formation of fibrils. In a word, a neutral environment is suitable for RA-based fibril formation, which provides a new insight for its future uses in food products.