Complementary roles of cellulose nanofiber and soy protein isolate for clean-label stabilization of plant-based...

Clean-label stabilization of plant-based emulsions often requires a combination of interfacially active proteins and polysaccharide networks. The present study examined the stability window of cellulose nanofiber (CNF)-soy protein isolate (SPI) emulsions by screening CNF:SPI ratios (0:10-10:0) and oil fractions (20-80%), and then focused on 40% oil for systematic evaluation. We determined the zeta potential (ζ), emulsifying activity/stability indices (EAI/ESI), droplet size distributions, confocal microstructure, and rheology to elucidate the complementary roles of CNF and SPI.

All emulsions were electrostatically stabilized, exhibiting zeta potentials between -31.5 and -49.9 mV, with increasing CNF fraction producing more negative surface charges. The SPI-only formulation generated small but polydisperse droplets (~15-80 μm) and displayed weak viscoelasticity, whereas the CNF-only system produced coarse, bimodal droplets (20-100 μm) despite a strong surface charge. By contrast, mixed formulations, particularly C8S2-C6S4, formed uniform droplets (10-20 μm), demonstrated broad linear viscoelastic ranges, and showed pronounced shear-thinning behavior. Among them, C6S4 achieved the highest EAI = 8.18 m² g^-1 and ESI = 70.4 min, together with the largest critical strain = 68.5%, indicating the most effective synergy between interfacial protein film formation and CNF-reinforced bulk network. These findings quantitatively confirm that balanced CNF:SPI ratios yield optimal structural stability and rheological performance for clean-label plant-based emulsions.

These findings support a cooperative mechanism: SPI furnishes elastic interfacial films, whereas CNF reinforces the continuous phase via a weak fibrillar gel network. Balanced CNF:SPI ratios (C6S4-C8S2) optimize droplet uniformity, electrostatic repulsion, and bulk viscoelasticity. These results provide practical design rules for obtaining robust clean-label plant-based emulsions. © 2025 Society of Chemical Industry.