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United States Department of Agriculture

Agricultural Research Service

2007 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
We obtained new knowledge about which amounts of tocopherols inhibit oxidation and deterioration in purified frying oils using tortilla chips as a food system. We found that gamma and delta tocopherols inhibited oxidation of the aged tortilla chips fried in mid-oleic sunflower oil the best, followed by alpha tocopherol. None of the tocopherol homologues had an effect in extending the fry life of oil. We obtained new knowledge on the effects of various amounts of phytosterols in purified oils on enhancing oil stability during heating and frying. We found that the primary phytosterols existing in commodity oils such as soybean and sunflower did help to inhibit the deterioration of soybean oil heated at frying temperatures. Their addition extended the fry life of the oil. The additive combination of phytosterols to inhibit frying oil deterioration and tocopherols to inhibit oxidation in the fried food provides important information in the search for alternatives to hydrogenated oil for frying. We arranged with ARS plant geneticists in Fargo, ND, to grow out large quantities of mid-oleic with high levels of gamma and delta tocopherols as an alternative to traditional mid-oleic sunflower, which has low levels of gamma and delta tocopherols. Enough seeds were planted to yield 8 pounds of oil that is processed into refined, bleached, and deodorized oil for end-use performance testing of the oil. This has extended the research beyond just extracting the seeds to test the oxidative stability of the crude oil as we have done in the previous years. We evaluated the levels of Maillard reaction products formed in expeller pressed soybean oils and in traditional hexane extracted soybean oils and found few differences in the levels between the two types of oil processing. We evaluated the frying stability of mid-oleic/ultra low linolenic soybean oil and the retention of the tocopherols during frying. Mid-oleic/ultra low linolenic soybean oil had a fry life equal to hydrogenated soybean oil; however the mid-oleic/ultra low linolenic soybean oil retained more tocopherols than the hydrogenated soybean oil which helped to extend the shelf life of fried tortilla chips. 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.

Phytosterols may improve heat stability of oils. Vegetable oils from different sources naturally differ in content of phytosterols (for example, corn oil has twice as many phytosterols compared to soybean oil). The question investigated is whether the amount of phytosterols in a vegetable oil affects its stability to heat. We found that in soybean oil, adding phytosterols increased its heat stability, and that the higher the phytosterol content, the better the heat stability. In high-oleic sunflower oils, added phytosterols had no affect on heat stability, perhaps because the high-oleic sunflower oil is already inherently more stable. This will add to knowledge of the role of phytosterols in oil stability, and may be used by breeders for selecting plants with higher phytosterol content, or by vegetable oil processors, who may adjust their processing conditions to conserve phytosterols, or add back phytosterols lost during processing. The data was presented in May at the Annual Meeting of the American Oil Chemists' Society in Quebec City, Canada. This knowledge addresses Component I for "Quality Characterization, Preservation and Enhancement" for National Program 306 "Quality and Utilization of Agricultural Products."

Mid-oleic/ultra low linolenic soybean oil is better than hydrogenated soybean oil for frying. Food manufacturers and restaurants are seeking alternatives to hydrogenated oil for frying because of problems with trans fatty acids. To determine if a new oil, mid-oleic/ultra low linolenic soybean oil has the fatty acid and tocopherol composition for enhanced frying stability, we compared the fry life and fried food stability of this oil compared to hydrogenated oil. The foods fried in mid-oleic/low linolenic soybean oil had better flavor, longer shelf life and more tocopherol retention than did the hydrogenated soybean oil. This new oil has the potential to replace hydrogenated oil for commercial frying because of enhanced stability from its fatty acid and tocopherol profiles. This new knowledge addresses Component I for "Quality Characterization, Preservation and Enhancement," for National Program 306.

Investigation of phytosterol structure in relation to anti-polymerization activity in heated oils. Phytosterols are naturally occurring components in vegetable oils. There are hundreds of different phytosterols, but only five occur most commonly in vegetable oils. The question investigated is whether phytosterols with different structures, including the number and type of double bonds, affects their ability to prevent polymerization of vegetable oils heated to frying temperature. We found that phytosterols with no double bonds or with one double bond had little anti-polymerization activity. Phytosterols with two double bonds had slight anti-polymerization activity, but a phytosterol with three double bonds most significantly reduced the amount of polymers formed in heated soybean oil. This adds to the knowledge of the role of phytosterol structure on its function in heated oils. Eventually this knowledge will allow us to make recommendations to plant breeders in the selection of plants with optimum phytosterol compositions. The data was presented in May at the Annual Meeting of the American Oil Chemists’ Society in Quebec City, Canada. This knowledge addresses Component I for "Quality Characterization, Preservation and Enhancement", for National Program 306.

Corn dried distiller’s grain (DDG) extracts are high in phytosterols and antioxidants. Corn DDG is a by-product of the growing industry whereby ethanol is obtained from corn fermentation. It is currently sold at relatively low value as an animal feed. We found that oil extracted from DDG is high in naturally-occurring antioxidants, such as tocopherols, tocotrienols, and ferulate-phytosterol esters. It is also high in phytosterols, which are valued for their cholesterol-lowering properties. This knowledge provides a possibility for a value-added market for the DDG by-product. The valuable components could be initially extracted, leaving still a high protein and high fiber feed supplement. In addition, we are in the process of purifying some of these components to test their ability to stabilize oils during heating and frying. This knowledge addresses Component I for "Quality Characterization, Preservation and Enhancement", as well as Component II: “New Processes, New Uses, and Value-Added Foods and Biobased Products” for National Program 306.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of non-peer reviewed presentations and proceedings9

Review Publications
Warner, K.A. 2007. Frying oil deterioration. In: Akoh, C., editor. Food Lipids: Chemistry, Nutrition and Biotechnology. Boca Raton, FL: Taylor and Francis Company. p. 71-82.

Winkler, J.K., Rennick, K.A., Eller, F.J., Vaughn, S.F. 2007. Phytosterol and tocopherol components in extracts of corn distiller's dried grain. Journal of Agricultural and Food Chemistry. 55:6482-6486.

Last Modified: 4/17/2014
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