Chitosan and crosslinked chitosan nanoparticles: Synthesis, characterization and their role as Pickering emulsifiers

•Deprotonated and crosslinked chitosan nanoparticles were produced and analyzed.•Chitosan nanoparticles were able to stabilize emulsions of roasted coffee oil.•Higher hydrophobicity was observed for deprotonated than for crosslinked chitosan.•Deprotonated chitosan nanoparticles formed a network in the continuous phase.•Crosslinked chitosan nanoparticles acted as Pickering emulsion stabilizers. Chitosan has been modified in order to produce nanoparticles with promising characteristics in diverse food applications, e.g. Pickering emulsions. Chitosan deprotonation and ionic crosslinking with tripolyphosphate were assessed in this work. Chitosan nanoparticles produced by these two methods were characterized according to surface charge, particle size distribution, chemical structure, wettability and microstructure imaging. The nanoparticles’ performance in the formation of oil-in-water Pickering emulsions was studied by physicochemical and rheological assays. Chitosan nanoparticles produced by amino deprotonation were larger and resulted in emulsions with larger oil droplets, with rheological behavior of the emulsions being greatly affected by increasing concentration of chitosan, which formed a network structure in the continuous phase. On the contrary, the tripolyphosphate-crosslinked chitosan nanoparticles were smaller and produced emulsions with smaller droplets, which remained less viscous even when chitosan concentration was increased and showed evidences of Pickering stabilization when analyzed by microscopy techniques.