Author
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Warner, Kathleen |
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Submitted to: Antioxidants International Conference Proceedings
Publication Type: Abstract Only Publication Acceptance Date: 5/1/2004 Publication Date: 7/15/2004 Citation: Warner, K.A. 2004. Effects of antioxidants in frying oils [abstract]. Antioxidants International Conference Proceedings. p. 89. Interpretive Summary: Technical Abstract: In response to a lack of standard protocols for analyzing the effect of antioxidants in food oils, we have assembled procedures for evaluating the effects of antioxidants in vegetable oils. These protocols are for oils containing naturally occurring antioxidants; oils with added antioxidants; and purified oils that have been stripped of all minor oil constituents. The three basic portions of this presentation are: 1) principles for antioxidant studies of food oils; 2) protocols for oxidizing oils with antioxidants; and 3) protocols for measuring the amount of oxidation and therefore the effectiveness of the antioxidants in inhibiting oxidation. E.N. Frankel (1) has published the basic principles on which these procedures are based. First, oils (oil or triacylglycerols) with antioxidant(s) should be evaluated under various conditions of oxidation (temperature, light, metals). Avoid the use of free fatty acids because they form micelles and of fatty acid methyl esters because the effect of antioxidants is different than in triacylglycerols. Second, use various oxidation conditions including different temperatures (between ambient and 60 deg C), metal catalysts, and/or agitation. Avoid high temperatures because the mechanism for oxidation is different at high temperatures (above 60 deg C) than at ambient temperature. Avoid high oxidation levels (e.g. peroxide values higher than 20-30) because they are not relevant to actual food samples since they exceed normal levels of rancidity. Third, several methods should be used to measure different and specific products of oxidation related to the quality of the oil. To determine level of oxidation, measure both initial primary oxidation products (hydroperoxides, peroxides, conjugated dienes) and secondary decomposition products (carbonyls, volatile compounds). In food-based oil systems, sensory evaluations should be conducted to confirm results from instrumental and chemical analyses used to measure oxidation products. Use methods that are sufficiently sensitive to measure relatively low levels of oxidation (below 0.1% or peroxide values below 5). Methods that measure specific oxidation products such as volatile compounds (e.g. aldehydes) are preferable to methods that measure non-specific compounds or changes in the oil such as the TBA test, weight-gain, oxygen absorption, and decrease of linoleic or linolenic acid. Recommended methods to oxidize the oil are the AOCS 'Oven Storage Test for Accelerated Aging of Oils' (Cg 5-97) (2) for autoxidation in the dark and AOCS 'Light Exposure Procedures for Oils' (Cg 6-02) (2) for photooxidation. To measure levels of oxidation, samples should be analyzed by more than one method and should include analyses of primary oxidation products such peroxides (AOCS method Cd 8b-90 (97)) (2) or conjugated dienes (AOCS method Ti 1a-64 (97)) (2). Secondary oxidation products such as volatile compounds (AOCS method Cg 4-94 (97)) (2) and p-anisidine (AOCS method Cd 18-90 (97)) (2) should also be analyzed because they correlate well with flavor. Odor and flavor analysis by trained sensory judges is recommended for food oils (AOCS Recommended Practice 'Flavor Panel Evaluation of Vegetable Oils' Cg 2-83 (97) (2) or ASTM Standard Practice E 1627-94 'Standard Practice for Sensory Evaluation of Edible Oils and Fats' (3). Set a defined end point, relative to the goal of the experiment prior to initiating the project. For example, a typical end point is the number of hours to reach a peroxide value of 10 or 20 meq/kg. 1. Frankel, E. N. Lipid Oxidation, Oily Press, Dundee, Scotland, 1998, pp. 129-160. 2. AOCS Official Methods and Recommended Practices, 5th edition, AOCS Press, Champaign, IL (1998). 3. American Society for Testing and Materials, vol. 15.07, Annual Book of ASTM Standards, West Conshohocken, PA (2003). |
