The growth of gold nanoparticles via chemical reduction of HAuCl4 dispersed in gelatin-silicate mixtures was studied. Gelatin leads to densely packed nanoparticles whereas open colloidal aggregates with tight boundaries are formed within silica. Within the bio-hybrid systems, gold species are located within the gelatin-silicate particles and/or within the gelatin phase, depending on the preparation conditions. These various localizations and their impact on the final nanoparticle structure are discussed considering attractive and repulsive electrostatic interactions existing between the three components. These data suggest that bio-hybrid systems are interesting and versatile interfaces to study crystallization processes in confined environments.