Particle characteristics and tribo-rheological properties of soy protein isolate (SPI) dispersions: Effect of heating and incorporation of flaxseed gum

To understand the heat treatment and flaxseed gum (FG) on the properties of commercial spray dried soy protein isolate (SPI), SPI dispersions were prepared with mass ratio of 6 %, 9 %, and 12 % in water and the corresponding protein concentrations of 2.2 %, 3.61 % and 5.23 % were reached after centrifugation. The solutions were treated at different temperatures (25, 75 and 100 degrees C) and the particle characteristics and physical properties of the resulted samples were determined. The influence of different concentrations (0.05 % to 0.3 %) of FG addition was evaluated in the SPI solution at 5 % protein concentration. The results showed that heating caused decrease of particle size of the SPI proteins and 100 degrees C heat treatment caused decrease of hydrophobicity and viscosity of the protein dispersions, and increase of their physical stability, and the effect was more marked at high protein concentration; while heat treatment at 75 degrees C caused substantial increase in protein hydrophobicity and viscosity, and decrease of stability. Addition of FG resulted in increase of particle size, absolute value of zeta potential and hydrophobicity of the protein solutions. The viscosity of the solution was decreased with addition of FG, but higher FG concentration could lead to higher viscosity. The physical stability of the mixed system was improved at low FG concentrations, but decreased at concentration higher than 0.2 %, which was more significant after 100 degrees C heat treatment. FG incorporation could improve the boundary lubrication of the protein solutions.