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United States Department of Agriculture

Agricultural Research Service

Research Project: ENHANCING FLAVOR QUALITY AND OXIDATIVE STABILITY OF EDIBLE VEGETABLE OILS WITH PHYTOCHEMICAL ANTIOXIDANTS
2006 Annual Report


1.What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? Why does it matter?
Edible vegetable oils account for 75% of the U.S. production of vegetable oils or approximately 16 billion pounds each year. Vegetable oils intended for high stability uses such as frying currently need additional processing such as hydrogenation and chemical additives to be suitable for the 8 billion pounds/per year frying oil industry. Food manufacturers are currently looking for alternatives to hydrogenated oils because of trans fatty acids; however, oils that are processed without hydrogenation are not stable enough for frying oils. Most oils with fatty acid compositions modified to increase oleic and/or to decrease linoleic or linolenic acids are still not as stable for frying as hydrogenated oils. Naturally occurring minor oil constituents such as tocopherols and phytosterols could further enhance the stability of modified oils to have equal or better stability than hydrogenated oils. However, not enough information is available on how these phytochemicals affect product quality, stability, and end use performance. Basic research is needed to determine the relationship between product composition and desired flavor quality and stability attributes in soybean, sunflower, corn and other oils. Technologies are also needed to process oils to have better yields of naturally occurring antioxidants. If not enough appropriate edible oils for high stability applications can be produced in the U.S., food manufacturers may look to imported tropical fats such as palm or coconut as alternatives. We are developing new knowledge about naturally occurring phytochemical antioxidants in vegetable oils that affect the quality and inherent stability of edible oils. We are using various approaches to enhancing the flavor quality and oxidative stabilities of vegetable oils such as characterizing pressed oils to understand the sources of their enhanced stability. In other efforts to improve frying oil and fried food stability, we will add natural antioxidants to oils that lack the stability needed for high stability uses such as frying. We will make recommendations to food manufacturers, oil processors and plant geneticists to develop oils with enhanced stability using phytochemicals.

This project is in National Program 306 under "Quality and Utilization of Agricultural Products." This research contributes new knowledge to understand the roles of product composition for optimum end-use performance and quality of edible vegetable oils (problem area 1a on factors and processes that affect quality and problem area 1c on definition and basis of quality). This research also contributes to meeting the ARS goal for genetic improvement of oilseeds for improved attributes for good quality products in which plant breeders target particular quality attributes in the germplasm (problem area 1d on preservation and/or enhancement of quality).


2.List by year the currently approved milestones (indicators of research progress)
Year 1: Evaluate high gamma tocopherol sunflower oils; determine levels of oxidation products in frying oils; and evaluate pressed oils for frying stability.

Year 2: Optimize tocopherol ratios in vegetable oils; continue studies to determine levels of oxidation products in frying oils; continue to evaluate high gamma tocopherol sunflower oils; and continue studies to evaluate pressed oils for frying stability.

Year 3: Conduct studies with phytosterols; continue to optimize tocopherol ratios in vegetable oils; continue to evaluate high gamma tocopherol sunflower oils; and continue studies to evaluate pressed oils for frying stability.

Year 4: Continue to optimize tocopherol ratios in vegetable oils; continue to evaluate high gamma tocopherol sunflower oils; continue studies to evaluate pressed oils for frying stability; and continue to conduct studies with phytosterols.

Year 5: Continue to optimize tocopherol ratios in vegetable oils; continue to evaluate high gamma tocopherol sunflower oils; continue studies to evaluate pressed oils for frying stability; and continue to conduct studies with phytosterols.


4a.List the single most significant research accomplishment during FY 2006.
Expeller pressed low linolenic acid soybean oil--a trans-free alternative to hydrogenated oils. In continuing studies on expeller pressed oils as an alternative to hydrogenated oils for frying, we found that if low linolenic acid soybean oil is expeller pressed rather than processed conventionally by hexane extraction, the stability of the oil during frying is similar to that of hydrogenated soybean oil. The combination of expeller pressing and low linolenic acid soybean oil produced a better frying oil than either expeller pressed soybean oil or low linolenic acid soybean oil individually. This project is in National Program 306 under Component I for "Quality Characterization, Preservation and Enhancement." This research contributes new knowledge to understand the roles of product composition for optimum end-use performance and quality of edible vegetable oils (problem area 1a on factors and processes that affect quality and problem area 1c on definition and basis of quality). Currently, food manufacturers and commercial users of frying oils such as restaurants are in need of alternatives to hydrogenated oils for frying because of the trans fatty acid content imparted by hydrogenation. In pilot plant frying studies conducted by the ARS Potato Research Worksite in East Grand Forks, MN and in batch frying tests conducted at our research center, we found that low linolenic acid soybean oil that had been expeller pressed was superior to regular soybean oil that had been expeller pressed. Oil processors and food manufacturers now have new oil--expeller pressed low linolenic acid soybean oil--as a trans-free alternative to hydrogenation or added antioxidants in edible oils.


4b.List other significant research accomplishment(s), if any.
None.


4c.List significant activities that support special target populations.
None.


4d.Progress report.
In studies on the effects of expeller pressing of oils to enhance frying stability, we conducted pilot-plant continuous frying trials of potato chips and non-continuous batch frying trials of tortilla chips using oils including expeller pressed soybean oil, expeller pressed low linolenic soybean oil, partially hydrogenated soybean oil, high oleic sunflower oil, and corn oil. We found that the expeller pressed low linolenic acid soybean oil had better stability than the expeller pressed soybean oil. In most tests, the expeller pressed low linolenic acid soybean oil was as stable as hydrogenated soybean oil or high oleic sunflower oil. In studies to measure the phytosterols content of the frying oils, we found that corn oil had 2-3 times higher content than the other oils. Phytosterol content of the expeller pressed soybean oil was not higher than that of regular soybean oil. However, the phytosterol content of expeller pressed low linolenic soybean oil was higher than both expeller pressed regular, and hydrogenated soybean oil, indicating that there may be environmental or varietal influences on phytosterol content. Phytosterols were not susceptible to much loss in any of the oils during the continuous frying process. Corn oil had the highest loss at 5%. More phytosterols were lost during the batch frying process, most likely because the oil was used for a longer period of time. The formation of degradation products called polymers was lower during continuous frying than batch frying. During batch frying, the formation of polymers was highest in the regular soybean oil and expeller pressed soybean oil, probably because of their higher content of polyunsaturated fatty acids. The expeller pressed low linolenic soybean oil and the high oleic sunflower oil both had slightly less polymer formation than corn oil, while the hydrogenated soybean oil still had the lowest formation.

We conducted studies to determine the fate of tocopherol oxidation products in oil heated to frying temperatures. Some of our previous results have shown that tocopherols volatilize or disappear rapidly during frying. As tocopherols decompose during this process, they form breakdown products such as quinones also can have antioxidant properties. Since some quinones can act as antioxidants even after the tocopherols have decomposed, we conducted studies on oils heated to frying temperature and found that alpha tocopherol quinones levels increased as alpha tocopherol levels decreased in soybean and sunflower oils. The quinones themselves then decrease over time. This study showed that alpha tocopherol quinones are present in frying oils and may help to inhibit oxidation in frying oils and fried foods. These results could also help explain why oils that lose all of their tocopherol content still have some inhibition to oxidation.

We recommended that ARS plant geneticists develop sunflowers with high levels of gamma and delta tocopherols as an alternative to traditional sunflower, which has low levels of gamma and delta tocopherols. We evaluated oil extracted from sunflower seeds bred to have high levels of gamma and delta tocopherols and found that the oil was significantly more oxidatively stable than sunflower oil with the regular low gamma tocopherol content. These results are of interest to oil processors and food manufacturers in determining the appropriate antioxidant composition of oils such as soybean, sunflower, cottonseed, canola, and corn oils to maximize their quality for the 8 billion pound/year frying oil industry.


5.Describe the major accomplishments to date and their predicted or actual impact.
Two major accomplishments have been made during this project. First, we recommended that ARS plant geneticists breed sunflowers with increased levels of gamma and delta tocopherols. In the resulting cultivars, we found that crude sunflower oils extracted from the seeds were significantly improved in quality and stability if the tocopherol content was modified from its regular high alpha tocopherol content to high gamma and delta tocopherol content. More research is needed to grow out seeds that have the most effect on oil quality and to process the oil into deodorized oil to conduct full-scale frying studies. This information will be used by plant breeders in the future when issues such as yield and cost are resolved. This project is in National Program 306 under Component I for "Quality Characterization, Preservation and Enhancement." This research contributes to meeting the ARS goal for genetic improvement of oilseeds for improved attributes for good quality products in which plant breeders target particular quality attributes in the germplasm (problem area 1d on preservation and/or enhancement of quality). Second, in continuing studies on expeller pressed oils as an alternative to hydrogenated oils for frying, we found that if low linolenic acid soybean oil is expeller pressed rather than processed conventionally by hexane extraction, the stability of the oil during frying is similar to that of hydrogenated soybean oil. The combination of expeller pressing and low linolenic acid soybean oil produced a better frying oil than either expeller pressed soybean oil or low linolenic acid soybean oil individually. This project is in National Program 306 under Component I for "Quality Characterization, Preservation and Enhancement." This research contributes new knowledge to understand the roles of product composition for optimum end-use performance and quality of edible vegetable oils (problem area 1a on factors and processes that affect quality and problem area 1c on definition and basis of quality). Currently, food manufacturers and commercial users of frying oils such as restaurants are in need of alternatives to hydrogenated oils for frying because of the trans fatty acid content imparted by hydrogenation. In pilot plant frying studies conducted by the ARS Potato Research Worksite in East Grand Forks, MN, and in batch frying tests conducted at our research center, we found that low linolenic acid soybean oil that had been expeller pressed was superior to regular soybean oil that had been expeller pressed. Oil processors and food manufacturers now have new oil--expeller pressed low linolenic acid soybean oil--as a trans-free alternative to hydrogenation or added antioxidants in edible oils.


6.What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end-user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products?
Based on studies of sunflower oils from seeds bred to have high levels of gamma and delta tocopherols, we recommended that ARS plant geneticists develop sunflower seeds with specific amounts of alpha, gamma and delta tocopherols. During the 2006 growing season, the seeds from these cultivars will be harvested and sent to our research center for analysis. These sunflower seeds have the potential to be a value-added product within the next several years. The initial higher cost of seeds with modified tocopherol content will probably affect the use of this oil. In addition, new knowledge about the trans-free alternatives to hydrogenated frying oil such as expeller pressed oil has been developed and transferred to oil processors and food manufacturers through presentations, publications, workshops, short courses and visits with company representatives. They can use this information to develop new oils that will provide healthful, better tasting foods. In addition, plant breeders can use this information to develop new cultivars of oilseeds with enhanced profiles of tocopherols.


7.List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: List your peer reviewed publications below).
Warner, K. 2005. Loss of tocopherols in frying oils, fried foods and salad oils, 26th World Congress and Exhibition of the ISF, Prague, Czech Republic.

Warner, K., Glynn, M. 2006. Effects on quality and oxidative stability of snack foods fried in expeller pressed oils. Institute of Food Technologists Annual Meeting, Orlando, FL.

Warner, K., Miller, J.F., Demurin, Y. 2006. Oxidative stability of crude mid-oleic sunflower oils from seeds with high gamma and delta tocopherol levels. Annual Meeting and Expo of the American Oil Chemists Society.

Warner, K. 2006. Flavor development in high stability oils during frying. Annual Meeting and Expo of the American Oil Chemists Society.

Warner, K. 2006. Trans-free frying oils--Alternatives to hydrogenated fats. Trans-free Workshop, Oklahoma State University, Stillwater, OK.

Warner, K. 2006. Characteristics of frying oils and fried foods. Short Course on Frying Oils, Institute of Food Technologists, Chicago, IL.

Winkler, J.K., Warner, K., Glynn, M.T. 2006. Effect of deep-fat frying on phytosterol and polymerized triacylglycerol content in oils with differing fatty acid composition. Annual Meeting and Expo of the American Oil Chemists Society.


Review Publications
Warner, K.A., Dunlap, C.A. 2006. Effects of expeller pressed/physically refined soybean oil on frying oil stability and flavor of french-fried potatoes. Journal of the American Oil Chemists' Society. 83(5):435-441.

Warner, K.A. 2005. Effects on the flavor and oxidative stability of stripped soybean and sunflower oils with added pure tocopherols. Journal of Agricultural and Food Chemistry. 53(26):9906-9910.

Warner, K.A. 2006. Methods of analysis to determine the quality of oils. In: Gunstone, F., editor. Modifying Lipids for Use in Foods. Cambridge, UK: Woodhead Publishing Ltd. p. 15-30.

Warner, K.A., Glynn, M.T. 2006. Effects on quality and oxidative stability of snack foods fried in expeller pressed oils [abstract]. 2006 Institute of Food Technologists Annual Meeting and Food Expo. p. 23.

Warner, K.A., Miller, J.F., Demurin, Y. 2006. Oxidative stability of crude mid-oleic sunflower oils from seeds with high gamma and delta tocopherol levels [abstract]. 97th Annual Meeting and Expo of the American Oil Chemists' Society. p. 19.

Warner, K.A. 2006. Flavor development in high stability oils during frying [abstract]. 97th Annual Meeting and Expo of the American Oil Chemists' Society. p. 44.

Winkler, J.K., Warner, K.A., Glynn, M.T. 2006. Effect of deep-fat frying on phytosterol and polymerized triacylglycerol content in oils with differing fatty acid composition [abstract]. 97th Annual Meeting and Expo of the American Oil Chemists' Society. p. 89.

Lee, S., Warner, K.A., Inglett, G.E. 2005. Rheological properties and baking performance of new oat beta-glucan-rich hydrocolloids. Journal of Agricultural and Food Chemistry. 53(25):9805-9809.

Rennick, K.A., Warner, K.A. 2006. Effect of elevated temperatures on development of tocopherolquinones in oils. Journal of Agricultural and Food Chemistry. 54:2188-2192.

Last Modified: 4/20/2014
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