Stability of pea protein isolate-γ polyglutamic acid stabilised O/W emulsion: Effect of oil fraction, salt, and temperature

Pea protein isolate (PPI) exhibits amphipathic properties and low allergenicity. Nonetheless, the limited solubility of PPI at its isoelectric point (pI = 4.6) may hinder its efficacy in emulsion applications. Therefore, addressing this limitation of PPI is imperative. The present work thus investigated the influence of γ-polyglutamic acid (γ-PGA) on the quality of PPI-based emulsion. The results showed that as the concentration of γ-PGA increased from 0.05 to 0.50%, turbidity measurements for a PPI system within a pH range of 4.0 - 5.0 decreased from 0.79 to a minimum of 0.24, indicating that γ-PGA enhanced the hydrophilicity of PPIs, which might have been due to γ-PGA's ability to promote conformational stretching of PPIs. When oil fraction volume was increased from 1 to 3% (v/v), the emulsion particle size at pH 4.5 decreased from 2233.33 to 710.11 nm; however, further increase in oil volume resulted in larger emulsion particles. Compared with other groups with different oil volumes, the emulsion containing 3% (v/v) oil volume exhibited the lowest separation index during 21-day storage. Additionally, particle size and ζ-potential exhibited an increase with increasing NaCl concentration, indicating that the presence of ionic strength decreased the stability of the PPI-γ-PGA emulsion. Similarly, a corresponding increase in particle size was noted with increasing temperature. Consequently, the interactions between γ-PGA and PPI indicated a substantial potential for utilising γ-PGA in the stabilisation of PPI-stabilised emulsions under acidic conditions. The present work also provided fundamental theoretical insights into the application of PPI-γ-PGA emulsions across diverse environmental contexts.