Unravelling surface-active properties of unrefined ball-milled pistachio shell powder

This study explores for the first time the stabilizing potential of unfractionated pistachio shell powder (PSP), in emulsions and foams. PSP particles exhibited irregular morphology and a dry Dmax of ~9 µm, a high insoluble fraction (~87.5%), with 13% soluble content exhibiting surface activity at oil–water and air–water interfaces. Surface pressure kinetics revealed rapid interfacial adsorption of soluble compounds, likely involving low-molecular-weight surfactants and proteins. Despite low protein levels (1.06 ± 0.03%), PSP-stabilized emulsions displayed extremely small droplet sizes (Dmax = 15.6 ± 0.7 µm), suggesting a hybrid stabilization mechanism, as the droplets and the solid particles exhibited comparable sizes. Increasing PSP concentration reduced both droplet size and creaming, with full stability achieved close to 8% PSP. Confocal imaging confirmed limited interfacial anchoring of particles, supporting the predominance of soluble fraction in initial droplet formation and particle-driven network stabilization from the continuous phase. Foaming capacity was pH- and concentration-dependent: low PSP content (