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Author ORCID Identifier



Open Access Dissertation

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded


Month Degree Awarded


First Advisor

David Julian McClements

Subject Categories

Chemistry | Food Chemistry | Food Microbiology | Nutrition | Other Food Science | Polymer Chemistry | Toxicology


ε-Polylysine is an appealing FDA-approved, all natural antimicrobial biopolymer effective against a wide range of microorganisms. Its implementation is greatly limited by its strong cationic charge, which has been linked to instability in food systems, perceived astringency and bitterness, and the ability to inhibit lipid digestion. Previous studies have shown that controlled complexation of ε-polylysine with anionic pectin is able to prevent instability and astringency in simplified model food systems, while maintaining the antimicrobial character of polylysine. Isothermal titration calorimetry, micro-electrophoresis, microscopy, and turbidity analyses of the stability of electrostatic pectin-polylysine complexes in the presence of strongly anionic κ-carrageenan, and carrageenan-polylysine complexes in the presence of pectin at different mass ratios (pH 3.5) suggested that although polylysine-carrageenan interactions were much stronger, polylysine-pectin complexes maintained their stability in the presence of carrageenan.

In vitro digestion models showed that electrostatic interactions between bile salts and polylysine, which have been suggested as the mechanism for lipase inhibition by polylysine (2ppm), were affected by components in the sample’s matrix. The implementation of an anionic (quillaja saponin) versus a non-ionic surfactant (Tween 20) in corn oil emulsions (2.5%w/w) showed a marked decrease of lipase inhibition, suggesting that electrostatic complexes formed by polylysine with other components prior to its exposure to bile salts in the small intestine may prevent the lipase-inhibiting polylysine-bile salts complex from occurring.

Corn oil emulsions (2%w/w) stabilized by Tween 20 subjected to oral, gastric, and intestinal digestion in the presence and absence of mucin and polylysine (200ppm) demonstrated that polylysine forms electrostatic complexes with bile salt-stabilized mixed micelles, potentially decreasing lipid absorption and altering its metabolism. Complexes formed between polylysine and mucin prior to addition of bile salts showed a decrease in insolubilized oil after digestion, suggesting that interactions between polylysine and bile salts were somewhat inhibited.

The influence of polylysine and pectin on the in vitro digestibility of animal feed either as individual components or as an electrostatic complex was assessed as part of a subchronic toxicity study. While pectin appeared to increase the rate and extent of lipid digestion, there did not seem to be any inhibition generated by polylysine.