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Date of Award

2-2009

Access Type

Open Access Dissertation

Document type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

First Advisor

Eric A. Decker

Second Advisor

Fergus M. Clydesdale

Third Advisor

D. Julian McClements

Subject Categories

Agronomy and Crop Sciences

Abstract

Lycopene has recently received interest as an antioxidant in human tissues. These same antioxidant properties present challenges in preventing oxidative degradation within food products. In this research, degradation of lycopene in model emulsion systems was examined to better understand the chemical stability of this potential functional food ingredient.

Lycopene in corn oil or hexadecane was used to make oil-in-water emulsions using small molecule surfactants. Emulsion color loss was used to estimate lycopene loss and was monitored using an integrating sphere. Lipid hydroperoxide and hexanal formation was used to monitor the development of lipid oxidation.

Oxidation and color loss were found to be influenced by surfactant type, with the fastest rates occurring in emulsions stabilized by anionic sodium dodecyl sulfate (SDS) and slower rates occurring in emulsions stabilized by cationic dodecyltrimethylammonium bromide (DTAB) and nonionic Brij 35. Lycopene oxidized in the presence and absence of unsaturated fatty acids, suggesting that degradation can occur by mechanisms that do not involve lipid oxidation products.

Further understanding of the mechanisms of lycopene degradation was gained by exposing emulsions to light, varied pH, a metal chelator, and a free radical scavenger. Results suggest that transition metal induced oxidation of lycopene may be the predominant mechanism of degradation at low pHs where transition metal solubility is high. At higher pHs, where metal solubility is lower, attack by free radicals was also found to be contributing to lycopene oxidation.

The role of ferric and ferrous species of iron in lycopene degradation was also investigated. In SDS-stabilized emulsions, and in bulk hexadecane, lycopene was found to degrade fastest in the presence of ferric iron. Ferrozine chelation testing show that this degradation is likely due to the reaction of lycopene with ferric ions to produce the ferrous species and a lycopene radical cation. In nonionic, Brij 35 and Tween 20 emulsions, ferrous iron resulted in the most rapid lycopene degradation. While further work is needed to clarify these findings, results from ferrozine analyses suggests that ferrous ions may be oxidized to the ferric species by naturally present hydroperoxides present in the surfactants, and then go on to attack lycopene.

DOI

https://doi.org/10.7275/5648773

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