Pickering high internal phase emulsions
(HIPEs) stabilized by biological
particles have attracted growing interest. However, developing Pickering
HIPEs with bare zein particles (ZPs) is still a challenge. Here, we
demonstrated a facile method for the development of Pickering HIPEs
stabilized solely by bare ZPs. In brief, the pH value was adjusted
during the emulsification; thus, the aggregation of ZPs transferred
from the continuous phase of HIPEs to the oil–water interface.
In detail, the strong hydrophobicity of ZPs was changed into intermediate
wettability after changing pH, as indicated by the value of the three-phase
contact angle (θ) decreasing from 108.4° to around 90°.
Through adjusting the assembly behaviors of ZPs, the interfacial and
continuous microstructures in the emulsification system were defined
accordingly, therefore forming stable Pickering HIPEs. Generally,
with the final NaOH concentration ranging from 0.6 to 2.0 mM in HIPEs
(pH 6.6–8.9), HIPEs with an internal phase volume fraction
of 80% were prepared successfully using pristine ZPs as sole eco-friendly
Pickering stabilizers. The microstructure of HIPEs featured that ZPs
deposited in situ at the oil–water interface,
forming an effective physical barrier, while the rest of ZPs that
remained in water phase functioned as the structural element and stacked
into a 3D network architecture, constituting another strong barrier
and facilitating the immobilization of oil droplets. This microstructure
contributed to satisfactory stability, good viscoelasticity behavior,
and ideal thixotropic recovery of HIPEs. Moreover, the HIPEs obtained
here served as the encapsulation system for probiotics, and they maintained
the viability of Lactobacillus plantarum at 4 °C. The facile method developed here paves the way for
preparing Pickering HIPEs stabilized by protein-based particles.
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