Microwave-assisted Extraction of Tomato Peels and Physicochemical Stability, In Vitro Bioaccessibility, and Cellular Uptake of Lycopene-Loaded Emulsions
Chronic disease is responsible for roughly two-thirds of deaths globally. Although a variety of factors contribute, phytochemical consumption may lower the risk of several diseases. Many phytochemicals act as functional pigments or antioxidants, can be found in manufacturing waste streams, and are often underutilized or discarded. Unfortunately, many phytochemicals are poorly extractable, unstable, and have limited bioavailability and efficient strategies must be developed in order to use these compounds. Lycopene, a hydrophobic and labile compound, was selected as a model carotenoid to investigate microwave-assisted extraction (MAE) and for developing a protein-stabilized emulsion delivery system. Dairy proteins are commonly used as emulsifiers due to their favorable functional properties; however, plant proteins offer a relatively sustainable alternative to reduce the dependence on animal-derived products. Thus, the objectives of this research were to: 1) determine the effect of MAE conditions on cis- and trans-lycopene recovery from tomato peels, a processing byproduct, 2) determine the effect of dairy or plant protein on lycopene-loaded emulsion physicochemical stability, 3) investigate the effect of mixed protein interfaces on interfacial rheology, and 4) assess in vitro bioaccessibility and cellular uptake of lycopene from emulsions. Findings indicated that MAE saved time by extracting significantly more all- trans-lycopene from tomato peels compared to a slower, conventional extraction. MAE-processed tomato peels exhibited more structural disruption compared to others, which may have allowed for better lycopene recovery. Pea protein stabilized emulsions by forming viscoelastic, interfacial protein films and retained lycopene similarly to casein, an industry standard. Interestingly, binary blends containing whey with soy or pea protein improved emulsion stability compared to those stabilized with only one protein. Despite having the best individual stability, casein exhibited antagonistic effects when blended with plant proteins. In vitro studies indicated that pea protein emulsions had a significantly lower micellarization efficiency, but significantly higher uptake efficiencies compared to whey emulsions, non-emulsified lycopene oil, and tomato paste. Mechanisms for interfacial film behavior and bioaccessibility were proposed as these findings open opportunities for future research endeavors. Overall, these results indicate that MAE reduces lycopene recovery time and that plant proteins have favorable functionality for the delivery of lipophilic bioactives.
San Martin-Gonzalez, Purdue University.
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