|M.Sc Student||Kuplennik Nataliya|
|Subject||Development and Investigation of Active Antimicrobial|
|Department||Department of Polymer Engineering||Supervisors||Professor Emeritus Moshe Narkis|
|Professor Ayelet Fishman|
|Full Thesis text|
In recent years much attention has been devoted to active packaging technologies which offer new opportunities for the food industry and food preservation. In the present study, two antimicrobial (AM) packaging prototypes were developed by combining a polymer matrix with a food preservative via melt compounding (prototype 1), or mixing with a commercial lacquer and applying the obtained mixture on a polymer film as a coating layer (prototype 2).
Different approaches were tested for dispersion of the polar potassium sorbate (KS) preservative in the apolar polymer matrix (LLDPE) and a new approach yielding a fine and thin KS dispersion was developed. This approach includes using glycerol monooleate (GMO) as a dispersant and preparation of a GMO/KS concentrate by strong mechanical mixing. Thermal stability of the blends prepared by all the approaches was not affected by the additives presence at temperatures relevant to LLDPE processing, i.e. 180-220°C, and at higher temperatures, the thermal stability was improved. Shear thinning behavior was observed in all the blends and rheological characterization revealed that additives insignificantly affected the apparent viscosity of the blends. Release tests showed that KS migrates from compression molded 300 μm films to an acidic food simulant and its diffusion obeys the Fickian diffusion rule. All of the prepared films had similar values of diffusion coefficient, 1.8-2.9?10-10 m2/h. The films prepared by the new approach showed a slightly higher antimicrobial activity against Saccharomyces cerevisiae S288C (2-3 log reduction) than those prepared by the other approaches (1-2 log reduction) due to the fine KS dispersion obtained, as was shown by HRSEM observations.
Working on the second AM packaging prototype, a comprehensive research for incorporation of preservatives into commercial lacquers applying several different methods, techniques and materials was performed. Nearly 150 different formulations were prepared and tested. It was shown that incorporation of sorbic acid (SA) into the EVA based lacquer by dissolving it in an appropriate solvent and then mixing with a lacquer, under continuous heating, resulted in a stable lacquer/preservative/solvent mixture. The formulations obtained with final 2, 3 and 4%w/w SA concentrations were applied as a single and a double coating layer on commercial polyethylene films. The coating weight of the double layer samples was approximately twice higher than that of the single layer samples, and in general higher than the acceptable application weight of dry lacquer - 6-8 g/m2. The presence of the SA and solvents in the lacquer resulted in a porous coating layer structure. Consequently, the higher was the SA concentration in the coating layer the higher was the release degree. Approximately 100% release was obtained for the 4%w/w SA coatings, compared to 22% for the 2%w/w SA coating. All coated films exhibited antimicrobial activity against S. cerevisiae S288C. Films coated with the lacquer containing 4%w/w SA as two layers manifested the highest antimicrobial activity, 3.5 log growth reduction.