Characterization of nisin containing chitosan-alginate microparticles

Nisin is a naturally occurring bacteriocin that has GRAS status for use in foods granted by the FDA. Encapsulation of nisin within microparticles can protect it from interactions with other food components, thereby increasing its stability and functionality. The effects of formulation parameters on the physico-chemical characteristics of nisin-loaded chitosan-alginate microparticles were studied. Chitosan-alginate microparticles were prepared using the ionotropic pre-gelation method, which involves inducing coiling of the alginate polymer by forming a calcium-alginate pre-gel state, and followed by chitosan complexation. Calcium-alginate pre-gel states were investigated using various calcium concentrations (0-5 mM) through viscosity measurements, and calcium concentrations below 2 mM were found to promote the formation of a coiled alginate nucleus. Calcium concentration had a significant effect (p < 0.05) on the size and zeta potential of microparticles. Nisin containing microparticles prepared using 2 mM calcium concentration had a particle size diameter of 7.86 +/- 0.34 mm, and zeta potential value of -10.6 +/- 1.22. The average polydispersity index (PDI) of particles was found to be 0.25 +/- 0.01, indicating a wide variation in particle sizes. SEM images revealed that the microparticles showed a tendency to aggregate, perhaps due to their low surface charge. Chitosan-alginate complex formation was confirmed using FTIR analysis, and the nisin peptide was found to be intact upon encapsulation, with no change in its secondary structure. (C) 2017 Elsevier Ltd. All rights reserved.