Investigating the effects of ion strength on amyloid fibril formation of rice proteins

Protein fibrillation is recognized as an attractive strategy to broaden and improve the function of food proteins. This research investigated the influence of different NaCl concentrations (0–210 mM) on the thermal aggregation behavior of rice proteins (RP) at pH 2.0. Under lower (<100 mM) and higher (>100 mM) NaCl concentrations, RP formed aggregates with different sizes and structures. At lower concentrations, the zeta-potential of RP increased from 14.3 mV to 22.8 mV during incubation, indicating that the electrostatic repulsion of RP was enhanced and numerous positively charged building blocks were generated. The circular dichroism (CD) results indicated that the native structure of RP was destroyed after heating at 90 °C for 24 h, and a secondary structure dominated by β-sheets (more than 50%) was formed. Proteins formed long fibrils after 24 h heating, as observed by atomic force microscope (AFM). However, at higher NaCl concentrations, the hydrophobic interaction was the dominant force due to electrostatic shielding. The protein aggregated randomly to form amorphous aggregates with particle sizes over 600 nm. This study will provide a new insight of RP-based fibrils in food application. • Adding a low concentration of NaCl promoted rice proteins fibrillation. • Rice proteins were easier to form amorphous aggregates at high NaCl concentrations. • Balancing electrostatic repulsion and hydrophobic interaction is key to be fibrils. • Proteins fibrillation improved the solubility and functional properties of proteins. • Peptides and positively charged construction are important components of fibrils.