Masters Theses

Date of Award

8-2008

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Qixin Zhong

Committee Members

P. Michael Davidson, Arnold M. Saxton

Abstract

A hydrophobic biopolymer, corn zein, was studied as a carrier for manufacturing particulate delivery systems of antimicrobials with sustained release. Three techniques, i.e., solvent attrition, supercritical anti-solvent and spray drying, were investigated to produce lysozyme-loaded zein micro- or nanocapsules. The work was focused on particle synthesis and in vitro release kinetics as affected by formulations and processes.

The size (100-200 nm) and morphology (separated or connected) of the zein nanoparticles produced using solvent attrition were significantly affected by shear force, ethanol and zein concentrations in stock solutions during synthesis. Zein nanoparticles showed gradual release of lysozyme at pH 7 and 8 but no sustained release at lower pHs. Further, the impact of adding 1% zein nanoparticles in model carboxymethylcellulose solutions (adjusted to pH 3 to 9) was studied for viscosities that increased with pH.

Microcapsules produced from supercritical anti-solvent showed a continuous matrix with internal voids. Sustained release of lysozyme at pH 2 to 8 was observed over 36 days at room temperature, with slower release at higher pH. At pH 4, release kinetics was further slowed by addition of sodium chloride.

Spray drying was studied as one commercially feasible process. To further reduce the material cost, partial purification of lysozyme from hen egg white was studied using binary aqueous alcohol. Extraction with 50% ethanol at pH 3.5 for 6 h enabled high lysozyme activity and relatively high purity. Lysozyme precipitated after increasing the ethanol concentration from 50% to 90% in the extract. The precipitates were resolubilized by dilution to 50% ethanol. Slurries after increasing ethanol concentration from 50% to 60%-90%, with or without additives of Tween 40 or thymol, were spray dried. Capsules without additives were porous and did not show sustained release of lysozyme. The addition of Tween 40 changed the capsule microstructure to packed nanoparticles but did not achieve sustained release of lysozyme. Thymol facilitated the formation of a continuous capsule matrix and allowed sustained release of lysozyme at near neutral pH.

Findings from this work demonstrated the possibility of using zein as a carrier biopolymer to deliver antimicrobials in food matrices for sustained release.

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