3.3.1. Effect of pH

As seen from Figure 3A, S/Z exhibited extensive aggregation at pH 3.0 and 4.0, exhibiting an increased particle size. This increase in size could be due to the fact that weakened electrostatic repulsion was weakened among binary nanoparticles. However, after adding CMC and ALG, compared to S/Z, the stability of both nanoparticles was enhanced noteworthily within pH 3.0 to 4.0. Most notably, from pH 3 to 9, both CMC/S/Z and ALG/S/Z had excellent stability. It is reported that certain zein-surfactant or zein-polysaccharide binary nanoparticles, such as zein-rhamnolipid, zein-alginate, and zein-chondroitin sulfate, experienced a significant size increase at low pH levels [34–36]. Unexpectedly, zein-surfactant-polysaccharide ternary nanoparticles exhibited superior pH stability. There are some yellow floccules in the bottom of the container of S/Z at pH 3.0 and 4.0 but no floccules in CMC/S/Z and ALG/S/Z (Figure S4).

**Figure 3.** Particle size of colloidal particles at different pH conditions (**A**) and different NaCl concentrations (**B**).

#### 3.3.2. Effect of Ionic Strengths

Particle size of S/Z was relatively low by 0 to 100 mM NaCl concentrations (Figure 3B). However, when increased to higher ionic strengths at 150~200 mM NaCl concentrations, precipitates were produced along with increasing particle size. This forming aggregation patterns for nanoparticles at high ionic strengths could be explained by increasing counterions (such as Cl− and Na+), depressed electrostatic repulsion via electrostatic screening and nanoparticle charge neutralization [21]. However, in the existence of CMC and ALG, the particle size of CMC/S/Z and ALG/S/Z was increased with the NaCl concentration increased. And adding CMC and ALG reduced the sensitivity of S/Z to aggregation under high ionic strength condition. There are two possible reasons for the improved physical stability of CMC/S/Z and ALG/S/Z. Firstly, CMC and ALG prevented counterion neutralization and strong electrostatic repulsions, which could potentially restrain complex particles from coalescence via enhancing repulsive forces among particles. Secondly, an increase of the steric repulsion among particles could have occurred as polysaccharide molecules were attached to S/Z. Some floccules were also observed at the bottom of the tube for S/Z at 150 and 200 mM NaCl (Figure S5). However, there were no floccules at the bottom of the tube for CMC/S/Z and ALG/S/Z, in which stable colloidal systems were both developed.
