Date of Graduation

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor/Mentor

Howard, Luke R.

Committee Member

Proctor, Andrew

Second Committee Member

Lay, Jackson O. Jr.

Third Committee Member

Prior, Ronald L.

Fourth Committee Member

McIntosh, Matthias C.

Keywords

Analytical; Anthocyanin; Chemistry; Color; HPLC; Natural

Abstract

Anthocyanins (ACYs) are polyphenol compounds found in nature, which contribute vivid colors to many fruits and vegetables, while also possessing significant health benefits. These pigments range in color from orange-red to blue-violet and could serve as natural colorants to replace artificial additives. There is a great demand from consumers to have fewer artificial compounds in their foods. However, the relatively instability of ACYs must be further understood in order to limit color degradation before they can completely replace synthetic colorants.

ACYs slowly degrade over time, but there is a knowledge gap on their fate and mechanisms causing degradation. In order to understand the mechanistic changes, different techniques were employed to understand ACY transformations over storage. Various types of solid phase extraction, high-pressure liquid chromatography columns, and gel electrophoresis analyses were used in an attempt to separate anthocyanin-tannin polymers by degree of polymerization. These compounds were detected using mass spectrometry, but separation by chromatographic techniques was not possible.

Ascorbic acid accelerates ACY degradation, but the mechanism was controversial. Model systems of a pure ACY, cyanidin-3-glucoside (C3G), and blackberry juice supplemented with ascorbic acid were prepared and hydroxyl radicals formed via the Haber-Weiss reaction. Hydroxyl radicals are highly unstable and reacted with C3G forming 6-hydroxy-C3G, which degrades faster than C3G. The combination of identifying the hydroxylated ACY using tandem mass spectrometry and detection the hydroxyl radicals via electron spin resonance verified the reaction mechanism of ascorbic acid catalyzed degradation of ACYs. Next, blackberry juice was supplemented with various additives to understand ACY stabilization mechanisms. Glutathione significantly improved anthocyanin retention over storage, so combinations of glutathione with lipoic and ascorbic acids were added to assess a potential antioxidant recycling mechanism. The combination was not more effective at stabilizing ACYs than glutathione alone. Finally, novel ACY compounds were created from radishes through a reaction originally found in wine fermentation. Using acetaldehyde as a polymerization agent, radish ACYs reacted with catechin to form stable pigments that were identified by mass spectrometry. This research furthers the understanding of anthocyanin reactions and degradation mechanisms, which improves their use as natural colorants in the food and beverage industry.

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