Effect of solvents and precipitant on the properties of chitosan nanoparticles in a water-in-oil microemulsion and its lipase immobilization performance

When chitosan nanoparticles were prepared in a water-in-oil (W/O) microemulsion by using 2% (wt) acetic acid (HAc) and 30% (wt) tri-n-octylamine (TOA) as solvent and precipitant, respectively, particle diameters of 7 nm were observed and the particles formed ovoid shaped aggregates. Using 0.05% HCl and 5.0 M NaOH as solvent and precipitant produced nanoparticles 10 nm in size that aggregated in the form of snowflakes. These two types of nanoparticles were used to immobilize lipase, the lipase adsorption capacity using nanoparticles 7 nm in size reached 156 mg/g and activity retention compared to free enzyme was as high as 66.7%, and the residual activity of the immobilized lipase was 91% after 5 runs of reaction. In additional, the activity retention of nanoparticles 10 nm in size also could reach 62.8%. This indicated that the chitosan nanoparticles prepared in a W/O microemulsion were suitable for lipase immobilization.