*3.3. Stability of Hollow Particles*

## 3.3.1. Salt Endurance

Colloidal stability against salt was assessed by exposing particles to various concentrations of NaCl. Quercetin-loaded hollow zein particles without and with chitosan were highly unstable and precipitated out even at 50 mM NaCl (Figure S2A,B), attributed to the screening effect and charge neutralization by counterions [7,43]. Quercetin-loaded HZchi/pec showed a remarkable endurance to precipitation up to 500 mM NaCl (Figure S2C). The size of quercetin-loaded HZ-chi/pec particles kept a single peak and increased gradually as the concentration of NaCl increased up to 200 mM (Figure 5A). Meanwhile, their ζ-potential changed to −29 mV (Figure 5B). It is possible that the NaCl ions screen the repulsion among the polysaccharide chain, leading to a greater adsorption of pectin on the particle surface [48,49]. These results are different from the sedimentation of pectin-coated zein particle at 70 mM NaCl reported by Huang et al. [16]. It can be thus speculated that the complex coating of chitosan and pectin provided better stability against salt than did by pectin alone. The size of quercetin-loaded HZ-chi/pec particles became bigger and had two peaks (Figure 5A), and their ζ-potential absolute values significantly decreased upon further increasing the concentration of NaCl. These results suggest the salt at high concentrations reduced the electrostatic repulsion between particles, resulting in their aggregation [46].

**Figure 5.** Size distribution (**A**) and ζ−potential (**B**) of quercetin−loaded hollow zein particles coated with chitosan and pectin as a function of NaCl concentration.
