Fluorescent complex coacervates of agar and in situ formed zein nanoparticles: Role of electrostatic forces

Herein, the complex coacervation between in situ formed spherical fluorescent zein nanoparticles and polyanion agar as function of mixing ratio (R = [Agar]/[Zein]) was investigated. This interaction yielded two distinguishable regions (at pH 5.4): Region I (R < 0.2), where fully charge neutralized soluble complexes with protein denaturation was noticed, and Region II (R > 0.2), where overcharged complexes were formed, with R = 0.2 defining the optimum binding. Small angle neutron scattering studies demonstrated that in the low-q region, nanoparticles formed the crosslink junctions and in the persistence regime of high-q region, the data captured the cross-sectional radius ( = 3.5 nm) for agar-zein complexes. The coacervates became more viscoelastic in salt-free samples because both the low frequency storage modulus and crosslink density were found to decrease with mixing ratio. Systematic decrease in storage modulus with ionic strength (0-0.01 M) implied screened Coulomb interaction was responsible for the observed coacervation. Further, we seek to find universality in complex coacervation of zein nanoparticle with biopolymers, and polysaccharides in particular.