Emulsion and interfacial properties of blended potato–lupin protein systems

The demand for plant-based proteins in emulsified foods has grown, necessitating deeper insights into how individual components and blends of plant proteins behave in oil-water systems. We examined potato (PPI) and lupin protein isolate (LPI), alone and in blends, at varying concentrations (1.0 %, 0.5 %, 0.1 %, 0.01 %) in oil-in-water emulsions produced by microfluidisation. Emulsions were analysed for droplet size distribution, and the protein content and protein composition of the aqueous phases were determined. Additionally, interfacial tension (IFT) was measured using pendant drop tensiometry. At 1.0 % total protein concentration, PPI formed small droplets (dx(50) = 0.83 ± 0.05 µm), whereas LPI exhibited median particle sizes around 3.45 ± 1.95 µm. The trend reversed at 0.1 % protein concentration. Blended systems showed significant droplet aggregation. Pendant drop tensiometry indicated that PPI effectively lowered IFT (9.19 ± 0.07 mN/m at 1.0 % total protein after 120 min), although adequate protein concentrations were necessary for a rapid decrease. LPI reduced IFT more rapidly at lower concentrations but maintained a higher IFT after 120 min compared to PPI at 1.0 % (11.55 ± 0.52 mN/m). In blends, the strong tension-lowering effect of PPI dominated at higher protein concentrations, while LPI fractions reduced IFT more rapidly at lower concentrations, highlighting a concentration-dependent interaction. Protein composition analysis confirmed that key PPI fractions readily adsorbed at the interface, while blending promoted depletion of selected lupin fractions from the continuous phase. The findings suggest that combining potato and lupin proteins can be used to tune emulsion properties in a concentration- and blend-ratio-dependent manner, offering valuable insights for formulating plant-based emulsions.