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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
2009 Annual Report


1a.Objectives (from AD-416)
To develop new knowledge about natural antioxidants that affect the quality and inherent stability of vegetable oils by investigating effects of tocopherols, tocopheron oxidation products and phytosterols and evaluating alternative technologies of oil processing.


1b.Approach (from AD-416)
We will conduct frying studies to evaluate the effects of various ratios of tocopherols for enhancing both the fry life of the oil and the shelf life of fried food. The effects of various phytosterols as antipolymerization agents will be investigated. Oxidation products from tocopherols such as quinones will be investigated as potential antioxidants. In addition, new cultivars of high gamma sunflower oil will be evaluated for frying stability in comparison with traditional low gamma/high alpha sunflower oil. We will use this information to recommend optimum levels and ratios of tocopherols in edible vegetable oils for both food manufacturers and plant geneticists. We will study alternative technologies such as pressing to retain better yields of natural antioxidants and produce oils with enhanced quality and oxidative stability. We will identify those inherent phytochemicals in pressed oils that positively affect oil quality and stability.


3.Progress Report
To help food manufacturers and food service operations improve the oxidative stability of frying oils and fried foods, without the need for trans fat-containing hydrogenated oils, we have developed new knowledge about the effects of natural oil constituents such as tocopherols and phytosterols as well as a new antioxidant to inhibit deterioration of frying oils and fried foods.

First, we found that the best profile of tocopherols in frying oils was a combination of three tocopherols--high gamma and delta tocopherols with low alpha tocopherol to keep frying oils and fried food from deteriorating. Adding the tocopherols individually was not as effective as all three tocopherols added together, indicating a possible synergistic effect. 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 so they can be used without hydrogenation.

Second, we found that phytochemicals extracted from distillers dried grain (DDG) oil significantly improved the oxidative stability of soybean, sunflower, and high-oleic sunflower triacylglycerols. Tocopherols, tocotrienols, and ferulate phytosterol esters in the oil all contributed to the antioxidant activity, though there may be other components in the DDG extract that also contribute to antioxidant activity. We have also isolated ferulate phytosterol esters from DDG oil that help to prevent polymerization in oils heated to frying temperatures. This is of interest to ethanol producers searching for additional markets for DDG, as well as to food processors seeking antioxidants and phytochemical compounds to enhance the nutritional properties of their food products. We are also investigating structure-function relationships of phytosterols by analyzing extracts from various plant sources such as soybean, sunflower, canola, Vernonia galamensis, and evening primrose oils which contain different profiles of some less common phytosterols. The phytosterols have been identified, and isolation is continuing. We are determining if there are differences in the antipolymerization activity of phytosterols from different plant sources and if there are any differences in activity of phytosterols with delta-5 double bonds versus delta-7 double bonds. This data will assist plant breeders in determining the best phytosterol profile to breed for better oil stability. Third, we determined that a new citric acid-based antioxidant that is heat stable to frying oil temperatures inhibits the deterioration of soy oil and food fried in it. This additive inhibited the formation of free fatty acids and total polar compounds in the frying oil and the development of off-flavor compounds in the fried food. This additive can be used as an alternative to hydrogenated oil to increase the stability of frying oil and fried food.


4.Accomplishments
1. Improving soy oil for frying with high temperature natural antioxidant. High temperature natural antioxidant improves soy oil for frying and increases the shelf life of food fried in oil containing the additive. As a result of limits on the use of trans fat-containing hydrogenated oils for frying in some areas of the U.S., some frying operations have chosen to use commodity (regular) soybean oil. Although regular soybean oil is excellent for salads and home use cooking, it is not typically used for frying in restaurants or by fried food manufacturers because it deteriorates easily at the high temperatures used for frying. Therefore, methods are needed to help improve regular soybean oil so it does not deteriorate in quality during commercial frying. We found that a new citric-acid based antioxidant not only increased the frying life of regular soybean oil when compared to the same oil without the antioxidant, but also extended the shelf life of food fried in the oil in comparison to food fried in soybean oil with no additives. This new antioxidant helps to improve the quality of commodity soybean oil so that is may be used for commercial frying and results in better tasting, more healthful fried food for the consumer.

2. Antioxidant activity of phytochemical extract from distiller’s dried grain oil. Phytochemicals were concentrated in an extract of distiller’s dried grain oil using molecular distillation. This extract was tested for antioxidant activity in soybean, sunflower, and high oleic sunflower oil triacylglycerols. The phytochemical extract increased the oxidative stability of the triacylglycerols. Therefore, extracts from distillers dried grain oil have potential use as antioxidants in vegetable oils and in foods to increase shelf-life. This also provides a value-added use for oil extracted from distiller’s dried grains, which is important for the economic stability and growth of the ethanol industry.


6.Technology Transfer

Number of Invention Disclosures Submitted1

Review Publications
Lee, S., Inglett, G.E., Palmquist, D.E., Warner, K.A. 2008. Flavor and texture attributes of foods containing beta-glucan-rich hydrocolloids from oats. LWT - Food Science and Technology. 42(1):350-357.

Warner, K.A. 2009. Flavor Changes During Frying. In: Sahin, S., Sumnu, S.G., editors. Advances in Deep-Fat Frying of Foods. Boca Raton, FL: CRC Press. p. 201-213.

Warner, K.A. 2009. Oxidative and Flavor Stability of Tortilla Chips Fried in Expeller Pressed Low Linolenic Acid Soybean Oil. Journal of Food Lipids. 16:133-147.

Moser, J.K., Warner, K.A. 2008. Effect of Phytosterol Structure on Thermal Polymerization of Heated Soybean Oil. European Journal of Lipid Science and Technology. 110:1068-1077.

Warner, K.A. 2009. High-Temperature Natural Antioxidant Improves Soy Oil for Frying. Journal of Food Science. 74(6):500-505.

Moser, J.K., Vaughn, S.F. 2009. Antioxidant Activity of Phytochemicals from Dried Distillers Grain Oil. Journal of the American Oil Chemists' Society. 86:1026-1035.

Last Modified: 4/19/2014
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