Drying mode and hydrothermal treatment conditions govern the formation of amyloid-like protein fibrils in solutions of dried hen egg white

Abstract

The recipe of some food products contains dried hen egg white (EW). It is convenient in use and available with a range of functionalities as a result of being stored under different time, temperature and moisture conditions following drying. Amyloid fibrils are fibrillary protein structures composed of highly ordered stacking of cross-β sheets. They can contribute to the foaming and gelling capacity of EW proteins. We here for the first time report that dried EW contains amyloid-like fibrils and that such fibrils in spray-dried EW (EWSD) are longer (ca. 100–200 nm) than those in freeze-dried EW [EWFD] (ca. 20–100 nm). In addition, conditions for optimal fibrillation were determined for both EWFD and freeze-dried ovalbumin (OVAFD) using a response surface design. Dilute solutions of OVAFD and EWFD were incubated at different pH values, times and temperatures. After storage at optimal conditions OVAFD [2.0% (wprotein/v), pH 7.0, 23 h, 76 °C] and EWFD [0.5% (wprotein/v), pH 7.0, 24 h, 85 °C], a higher level of cross-β sheet structures and larger worm-like protein fibrils were observed for OVAFD than for EWFD. Lastly, when EWSD stored for one week at either 50 °C and 50% relative humidity (RH) [EWSD 50°C/50%] or at 60 °C and 80% RH (EWSD 60°C/80%) was submitted to heating [0.5% (wprotein/v), pH 7.0, 24 h, 85 °C], a higher extent of fibrillation was found for EWSD 60°C/80% than for EWSD 50°C/50%. Thus, drying induces EW amyloid-like protein fibrillation. Also dry heating EWSD at 60 °C and 80% RH further enhances such fibrillation during heating in excess of water.