Preparation and Characterization of Chitosan-Alginate Nanoparticles for Trans-Cinnamaldehyde Entrapment

Abstract

Trans-cinnamaldehyde incorporated chitosan and alginate nanoparticles were synthesized using the ionic gelation and polyelectrolyte complexation technique. Alginate, chitosan, calcium chloride, and trans-cinnamaldehyde at predetermined concentrations were complexed electrostatically to optimize size and loading efficiency (i.e. preliminary study). A final extrapolated methodology using optimized processing parameters (e.g. stirring, homogenization, and equilibration time; droplet size) was developed and utilized for controlled release, morphological, thermal, antioxidant, and antimicrobial studies. The best working alginate to chitosan mass ratio was determined to be 1.5:1 at a pH dispersion of 4.7. Particle size (166.26 nm) and encapsulation efficiency (73.24%) were further optimized at this mass ratio using an alginate:calcium chloride mass ratio of 4.8:1, alginate:trans-cinnamaldhyde mass ratio of 37.5:1, 18 gauge syringe needle, stirring times of 90 minutes, 15 minutes of homogenization, and equilibration time of 24 hours. Optimized nanoparticles showed increased shelf life (6 weeks) and translucency in solution. Release tests showed trans-cinnamaldehyde release from loaded nanoparticles best followed the bioexponential model; a burst release function (32.5% cumulative release) followed by a sustained release function (62.31% final cumulative release). Differential scanning calorimetry confirmed inclusion of oil into nanoparticles by indirectly comparing thermal stability of free trans-cinnamaldehyde with loaded trans-cinnamaldehyde in the inclusion complex. Nanoparticles resembled a spherical shell and core type arrangement (i.e. spherical, distinct, and regular) and were in the size range of 10-100 nm. The final radical scavenging effect of loaded particles in apple juice was 62% and trans-cinnamaldehyde was just as available to react in free form as it was in inclusion complexes. Minimum inhibitory concentration values (MIC) for trans-cinnamaldehyde loaded nanoparticles was 7,031.25 μg/ml for Escherichia coli O157:H7 and 14,062.5 μg/ml for Listeria monocytogenes. The concentration of trans-cinnamaldehyde in the inclusion complexes corresponded to a MIC of approximately 730 and 1,4062 μg/ml of free trans-cinnamaldehyde for E. coli O157:H7 and L. monocytogenes, respectively. Results indicated that L. monocytogenes was more tolerant to the inhibition by trans-cinnamaldehyde inclusion complex in comparison to E. coli O157:H7. Overall, results suggest that the application of antimicrobial polymeric nanoparticles optimized for essential oil loading in food systems may be effective at inhibiting specific pathogens.