•Complex coacervation between zein and agar showed concentration dependent mixing.•Zein nanoparticles were formed in situ which immediately provoked coacervation with agar.•In salt-free coacervates, the material rigidity decreased with mixing ratio that make material more viscoelastic.•Storage modulus decreased with ionic strength due to screened Coulomb interaction.•At higher ionic strength, van der Waals forces played a key role in the coacervates. 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.