High Temperature Degradation of Fatty Acids: Cyclic Fatty Acid Monomers From Frying Oils, Their Formation and Potential Health Impacts

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Dietary fats are an essential part of the human diet since they are a concentrated source of energy and a major source of essential fatty acids (FA), and in general, Canadians recognize the beneficial health attributes of polyunsaturated FA. Their consumption of fats and oils for frying has been increasing over the years, because of changes in the eating habits favoring fried foods, notwithstanding the low-fat/no-fat diet trend. Heating of unsaturated vegetable oils results in thermolytic and oxydative reactions leading to the formation of degradation products such as trans and oxygenated FA, oligomers, and cyclic fatty acid monomers (CFAM). The degradation products are of serious concern from the standpoints of consumer health as well as the economics of operation for the food industry, and it is imperative to address this situation. Thus, the objectives of the research program are to gain a good understanding of the chemical reaction mechanisms leading to the decomposition of lipid molecules at frying temperatures, which would enable the development of methods to control those deteriorative reactions; and to assess their potential harmful metabolic effects. We have shown that the formation of CFAM and the rearrangement of conjugated systems in FAs result from peri-electronic reactions at high temperatures. Subsequently, we studied the kinetics of the formation of CFAM from a-linolenic acid (Ln) in order to understand the mechanisms, and identify the key intermediates in the formation of both 5- and 6-membered ring CFAM. Of particular note are our synthesis of a labeled (deuterium; 2H) and position-specific 6-membered ring CFAM, and metabolomics of this molecule in an animal model fed a diet containing low level (0.5% of total lipids). Either the composition of urine or the plasma alone could discriminate between the treated and control groups, where the levels of carnitines and lysophospholipids, indicators of lipid biosynthesis/use, were significantly reduced in the plasma of animals fed CFAM. We have also identified many metabolites of CFAM in both urine and plasma samples that indicated that CFAM undergo ß-oxidation and are typically eliminated as glucuronide, sulphate and nitrate conjugates. The results of this work constitute a significant progress towards our long term goal and have now paved the way to undertake studies on the production, characterization and metabolic effects of a potent new class of oxidation products from frying oils, the oxidized CFAMs (CFAM-Ox). We hypothesize that CFAM-Ox are formed in frying oils and may be have harmful metabolic effects, even at trace levels. This little known class of oxidized compounds, produced from frying oils, could exhibit certain analogous activities as those of the prostanoids, and consequently, they could interfere with critical biological reactions as well as signal transduction leading to altered physiology and incidence of diseases.