Characterization and Analysis of High Voltage Atmospheric Cold Plasma Treatment of Soybean Oil

Ximena V Yepez, Purdue University

Abstract

In 1900, Paul Sabatier was honored by the Nobel Prize for the invention the catalytic hydrogenation reaction, that changes the liquid oil into a solid fat. Although this reaction was used in many fields, the main application was to produce partially hydrogenated oils for the food industry. Catalytic hydrogenation achieves a reduction of polyunsaturated fatty acids, by a reaction that involves a catalyst, hydrogen gas, high pressure and temperature. However, this process creates the unwanted trans fatty acids. In 2015, after a century of research and development, the FDA announced that partially hydrogenated oils cannot be used as food ingredients, because trans fatty acids are associated with detrimental health effects. Today, emerging technologies are studied as effective tools to modify chemical structures of molecules. High voltage atmospheric cold plasma (HVACP) is a novel technology developed at Purdue University, which generates reactive species from gases such as hydrogen, nitrogen, or carbon dioxide. This technology not only reduces the microbial load of food, but also modifies the chemical structure of food ingredients. The overall objective of this project is to explore the feasibility of applying high voltage atmospheric cold plasma to modify the chemical structure of soybean oil by partial hydrogenation, without the use of a catalyst, high temperature, and trans fatty acids. The first study characterizes the effect of HVACP treatment of soybean oil and identifies changes in iodine value and fatty acid composition. This initial study constitutes a proof of concept, where HVACP treatment of 12h using 5% hydrogen-95%nitrogen gas produced a reduction to the iodine value from 130 to 90, a value similar to a commercial partially hydrogenated oil. In the second study, the objective is to increase the hydrogenation rate and reduce the treatment time by increasing the percentage of hydrogen gas in the plasma chamber. A processing time up to 1.5 h was evaluated with different concentrations of nitrogen and hydrogen gas. A short treatment time produced a reduction of IV from 130 to 123 in all gases. However, a fraction of the sample inside the plasma chamber was recovered from the top of the box, which had a higher exposure to reactive plasma species. This sample had a semisolid texture and an iodine value within the 80-90 range. These results suggest that a treatment with nitrogen and hydrogen gas modifies the chemical structure of soybean oil at similar rates. Additionally, HVACP is a surface treatment, that can be accelerated by increasing the sample’s surface area. The use of nitrogen gas was associated with a yellow color that appeared in samples treated with nitrogen gas, suggesting that nitrogen was absorbed in the triglyceride molecule. In the third study, an extensive analysis of HVACP hydrogenation of unsaturated double bonds by identifying reactants and products is developed, and a plasma hydrogenation reaction mechanism is proposed. Here, soybean oil, pure standards of linolenic acid and trilinolenin were treated with nitrogen, hydrogen, and argon gas. Results showed a hydrogenation reaction with all gases but mostly with nitrogen gas. It was proposed that the hydrogenation reaction may be achieved by hydrogen atoms from (a) water dissociation; (b) intermolecular re-arrangement; or, (c) hydrogen gas.

Degree

Ph.D.

Advisors

Kokini, Purdue University.

Subject Area

Chemistry|Agronomy|Atmospheric sciences|Food Science|Medical imaging

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