Release kinetics of nisin from chitosan-alginate films and microparticles

Open Access
Chandrasekar, Vaishnavi
Graduate Program:
Food Science
Doctor of Philosophy
Document Type:
Date of Defense:
April 30, 2015
Committee Members:
  • Ramaswamy C Anantheswaran, Dissertation Advisor
  • John Neil Coupland, Committee Member
  • Catherine Nettles Cutter, Committee Member
  • Ali Demirci, Committee Member
  • nisin
  • release
  • diffusion
  • chitosan-alginate
  • films
  • microparticles
Antimicrobials are being used to inhibit the growth of pathogenic and spoilage bacteria, thereby enhancing safety and extending the shelf-life of processed foods. Nisin is a bacteriocin that has Generally Recognized as Safe (GRAS) status, and is effective against Gram positive bacteria. Studies have shown that when nisin is directly applied to the surface of foods, it loses its biological activity over time. This loss is due to binding interactions with proteins and fats, and degradation by proteolytic enzymes, as well as due to diffusion into the bulk of the food. Delivery systems with sustained release properties of nisin have the potential to improve its stability and biological functionality in foods. Chitosan-alginate polyelectric complexes are an effective drug delivery tool used in the pharmaceutical industry for controlled release of antimicrobials. These materials can be used for controlled release of nisin as a film or microparticle system. The goal of this research was to develop and characterize chitosan-alginate films and microparticles containing nisin, and understand the release kinetics of nisin in an aqueous system. The specific objectives were (1) to determine the factors affecting release of nisin from chitosan-alginate films, (2) to determine the release kinetics of nisin from chitosan-alginate films and study component interactions, and (3) to evaluate the release kinetics of nisin from chitosan-alginate microparticles. The effects of polymer concentration (0.5 and 1.0%), chitosan molecular weight (low and high) and ratio of chitosan to alginate (expressed as 33, 50 and 66% alginate fraction) were investigated on the release of nisin from chitosan-alginate films. The polymer concentration and alginate fraction were found to have a significant effect (p<0.05) on nisin release. Highest nisin release was obtained for films prepared using 0.5% polymer concentration and 33% alginate fraction. SEM images indicated that the ratio of chitosan to alginate influenced the film microstructure. The release kinetics of nisin from chitosan-alginate films prepared using various alginate fractions (33, 50 and 66%) was investigated using a two-temperature agar diffusion bioassay. The total amount of nisin released from films into an aqueous system decreased significantly (p<0.05) with an increase in alginate concentration. The mechanism of diffusion of nisin from all films was found to be Fickian, and the diffusion coefficients varied from 0.87 x 10-9 to 8.03 x 10-9 cm2/s. Strong complexation was confirmed between chitosan and alginate polymers within the films, particularly at high alginate fractions. Binding between nisin and alginate was also confirmed, resulting in reduction of freely available nisin within films. Chitosan-alginate microparticles containing nisin, were produced by preparing a calcium-alginate pre-gel, followed by chitosan complexation. Calcium concentrations ranging from 0.25 to 2 mM were found to be effective in inducing the formation of a coiled alginate nucleus. Particles obtained were in the micrometer range. Calcium concentration had a significant effect (p<0.05) on particle size and zeta potential of microparticles. Burst release of nisin was observed from these particles into water. A diffusion-based model was developed to predict the nisin release from microparticles, and good agreement (R2 = 0.91) was obtained between model predicted data and experimentally measured nisin release. SEM images indicated that the microparticles were predominantly spherical or ellipsoidal in shape, with a tendency for particles to aggregate. Findings from this research will be useful for the development of efficient nisin delivery systems for food safety applications.