Date of Award
Doctor of Philosophy (PhD)
William S Whiteside
In this research a novel method for the rapid, direct measurement of oxidative lycopene degradation in oil-in-water emulsions via colorimetric means was developed. This analytical method was used to conduct experiments monitoring the degradation of lycopene-containing oil-in-water emulsions of decane spontaneously formed in the presence of nonionic surfactants (Span and Tween) of different tail lengths and molar ratios. The structure and ratio of these nonionic surfactants was manipulated to probe the mechanism of lycopene stabilization when iron-catalyzed oxidation was the main pathway of degradation, as controlled by pH and oil phase selection. The effect of addition of chloride salts with different cations was also investigated.
Optimum conditions for evaluation were developed using a Span 80/Tween 80 surfactant combination and lycopene extracted into decane from tomato paste. Using 0.5% FeCl3 concentration and ~2 millimoles surfactant at a pH of ~3, 2-hour degradation experiments were performed to evaluate various Span/Tween nonionic surfactant combinations for oxidative stability. Tails of lauryl (C12), myristyl (C14), stearyl (C18) and oleyl (C18:1 unsaturated) groups were evaluated. It was found that in general, for a fixed molar amount of surfactant, increasing the amount of Tween (hydrophilic surfactant) increased the stability of the lycopene emulsion. In addition, tail length of the surfactant plays a role in the stability of the emulsions with shorter, less hydrophobic tail lengths providing better oxidative stability.
Lithium, sodium, and potassium chloride were added to emulsions of lycopene in decane made with Span 20 and Tween 20 surfactants and evaluated for oxidative stability in iron-catalyzed conditions. It was found that stability decreased according to the Hofmeister Series for cations. The order of stability was found to be: K+ > Na+ > Li+. Increasing concentration of cation resulted in decreased lycopene stability for all cations.
Bowles, Jeffrey Allen, "Effects of Food-Grade Nonionic Surfactants on the Iron-Catalyzed Oxidative Stability of Lycopene in Oil-in-Water Emulsions" (2021). All Dissertations. 2909.