Colloidal stability of oil-in-water emulsions prepared from hen egg white submitted to dry and/or wet heating to induce amyloid-like fibril formation

Abstract

Hen egg white (HEW) proteins are components of some foods and improvement of their techno-functional properties has been widely studied. During food processing, they are commonly subjected to heating. Here, both the impact of dry, wet, and combined dry and wet heat treatment was investigated. Heating (1 h at 80 °C) dried HEW (still containing 12% water) resulted in formation of glycated Maillard compounds such as protein-glucose conjugates, but only in limited amyloid-like fibril (ALF) formation. Wet heating (0.5 h at 80 °C, in excess water) clearly resulted in increased relative Thioflavin T (ThT) fluorescence, indicating the formation of ALFs. When dry heating (0.5 h at 80 °C) was followed by wet heating (24 h at 80 °C), the slightly lower relative ThT fluorescence than obtained when wet heating HEW suggested that ALF formation was limited due to protein glycation. When control (i.e. unheated) HEW dispersions and dispersions containing different heated HEW samples were used as continuous phase for oil-in-water emulsions, control HEW resulted in a multimodal particle size distribution and high creaming rate. In contrast, emulsions stabilized by dry and wet heated HEW showed an overall reduced volume-weighted average droplet diameter (D43) and increased creaming stability. HEW subjected to 4 h dry heat treatment at 80 °C and 24 h wet heat treatment at 80 °C resulted in emulsions with a monomodal particle size distribution with the smallest D43 (0.47 ± 0.01 μm), as well as the lowest creaming rate (68.4 ± 9.77 mm/day). Comparison of the relative ThT fluorescence, D43 and creaming rate by principal component analysis revealed that mainly the emulsions with dispersions having high relative ThT fluorescence had lower average particle sizes and consequently a higher creaming stability. Thus, formation of ALFs by wet heating of HEW seems to be the better heat treatment for improving their techno-functional properties.