Heated fats

Soaps are the detergents used since long. Soaps used for cleaning purpose are sodium or potassium salts of long chain fatty acids, e.g., stearic, oleic and palmitic acids. Soaps containing sodium salts are formed by heating fat (i.e., glyceryl ester of fatty acid) with aqueous sodium hydroxide solution. This reaction is known as saponification. 

In relation to cancer, there is some evidence that highly oxidized and heated fats may have carcinogenic characteristics. HNE (4-hydroxy-2-frans-nonenal), a secondary lipid peroxidation product derived from linoleic acid oxidation, has assumed particular interest because it has shown cytotoxic and mutagenic properties. Its toxicity, as well other secondary lipid peroxidation products (HHE 4-hydroxy-2-frans-hexenal and HOE 4-h yd roxy-2-trans-oc ten al), is explained through the high reactivity with proteins, nucleic acids, DNA, and RNA. Research links them to different diseases such as atherosclerosis, Alzheimer s, and liver diseases (Seppanen and Csallany, 2006). Research is rapidly progressing, but results are still not conclusive. 

The isolation and structure elucidation of dimers formed as the result of thermal oxidation of fats during deep frying has been of great interest. However, the compositional determination of this fraction from used or heated fats and oils has been neglected because of the difficulties encountered during the isolation of dimers from heated fats and the complexity of the structures present within this fraction. 

Aitzetmuller (69,70) indicated that SEC can be used as a measure and indication of the extent of heating and polymerization of heated fats and oil. Harris et al. (71) achieved SEC separation of monomer, dimer, and trimer acids within 3 h, and quantitation was possible with the use of heptanoic acid as internal standard. 

Space does not allow a complete citing of the literature on thermal decomposition of lipids. Nor was it intended to list the hundreds of products which were identified in heated fats and rationalize mechanisms for their formation. The above discussion is an attempt to identify certain factors which influence the fate of lipids in complex biological systems when subjected to high temperature. It should be obvious that the potential for the mulitiple reactions and interactions which could take place in such systems is enormous. 

Other investigators (7-9) have identified a large number of carbonyls from heated fat. The remaining meat aroma components derived by heating lipids are esters, lactones, alkan-2-ones (methyl ketones), benzenoids and other alkylfurans. Several investigators have analyzed volatile compounds formed during thermal degradation of fatty acids (10-12). 

Smoke Point. As oils or fats are heated, a thin bluish smoke appears. The smoke point is the lowest temperature, under controlled conditions, that the smoke becomes visible. Cottonseed oil s smoke, fire, and flash points, like other fats and oils, are almost entirely dependent on the free fatty acid content. Fats and oils smoke point results decrease when the triglycerides are split during hydrolysis to form free fatty acids and glycerol. The glycerol portion decomposes to form acrolein, which is the major portion of the smoke evolved from heated fats and oils. Like other long-chain fatty acid oils, cottonseed oil with 0.01% free fatty acid will have a smoke point of approximately 450°F. Additions of monoglycerides... 

When it is necessary to heat fats to keep them fluid, heat should be applied to line, pumps, and tanks. Although insulation may be used to retain the necessary amount of heat, the abihty to apply heat in emergency situations is most desirable. Occasionally, even when shortenings are held above their apparent melting point, hard fractions will separate or seed out or fractionation will take place. In effect, the composition of the fat changes in different levels in the tank and possibly can block the lines. Application of heat and agitation may be necessary to correct the problem. It is recommended that experimentation on the product be carried out at the projected temperatures and times to ensure that this problem will not occur under operating conditions in the plant. 

Animal tissue cells grown in culture medium in the form of a monolayer are a useful biological living model to observe physiological, morphological or metabolic changes in the presence of compounds added to the medium. Bird and Alexander (15, 37) reported on effects of thermally oxidized corn oil and olive oil on in vitro heart cells. The DNUA from fat thermally oxidized as described earlier (7) was isolated. Free fatty acids from the fresh fat controls or from the DNUA of the heated fats were prepared (38). 

Figure 1. Histological scores for organs of rats intubated with fresh fats (O) or DNUA of heated fats (%). (Reproduced with permission from Ref. 31. Copyright...

The most consistent change in cultures exposed to heated fats was associated with intracellular lipid accumulation, which occurred rapidly (Figure 6). Prolonged exposure produced abnormal spherical cells filled with lipid droplets. They contained constricted, centrally located nuclei. Karyorrhexis and karyolysis were observed, and vacuolation and a network appearance were pronounced due to oxidized fat (Figure 7). The pyknotic nuclei as a percentage of the total number of cells in 20 random fields were increased due to heated fat fractions (Table IX), and accompanied the cytoplasmic changes seen earlier. Lipid droplet accumulation was estimated as shown in Table X, and the free fatty acids from the fresh fats induced less lipid accumulation. Nevertheless, the values for 00 were as high as those for HCO. 

Mitotic indices as a percentage of total number of cells in 20 random fields are shown in Table XI. Heated fat suppressed the rate of mitosis with the greater effect shown by HOO. In Figure 8, some tripolar spindles were observed among the dividing cells in the presence of HOO. 

Cultured heart cells responded rapidly to fatty acids administered to the medium. Heated fat produced lower levels of unsaturated fatty acids in the PL fractions, and a greatly increased level of arachidonic acid in the TG fractions (15) In the livers of rats fed heated fats, Rao et al. (50) showed a rapid rate of elongation and desaturation of fatty acid chains. 

Palmitic acid is preferentially taken up by the myocardium and used for synthetic reactions or as an energy source (51), and it has been shown to be important in the beating activity of heart cells in culture (52). Treatment of cells with heated fats resulted in a substantially reduced incorporation of labeled palmitic into the PL fraction, and an increased incorporation into the TG fraction (37). This would indicate that PL synthesis was inhibited due to heated fat treatment, and there was an impaired mobilization of TG fatty acids. Oleic acid is known to promote fat accumulation in tissue culture cells (53). The HOO treatment which provided most oleic acid gave the highest TG values. 

The French chemist Michel Eugene Chevreul (1786-1889) spent the first part of an incredibly long professional life in an investigation of fats. In 1809, he treated soap (manufactured by heating fat with alkali) with acid, and isolated what are now called fatty acids. Later, he showed that when fats... 

The endothelial dysfunction during the postprandial phase after a meal rich in oxidized fat is almost certainly due to the cellular response to oxidized fat originating from this repeatedly heated fat. As in so many cases, the precise identity of this factor is not known. It is often assumed that it is a reactive molecule, derived from quantitatively the most important unsaturated fatty acid (linoleic acid) in the diet. Thus 9-, 11-, and 13-hydroperoxy-linoleic acids are possibilities, as are 8,9- or 11,12-epoxy-linoleic acids. However, the relative amount of epoxy fatty acids in the diet is much less than that of hydroperoxy fats. Photooxidation products of oleic acid cannot be excluded either, and it is worth pointing out that this unsaturated fatty acid is quantitatively the most important fatty acid in Western and Mediterranean diets. What is also not clear is whether endothelial dysfunction during postprandial lipemia requires the induction of enzymes. 

Le Quere, J.-L., J.-L. Sebedio, R. Henry, F. Couderc, N. Demont, and J.-C. Prome, Gas Chromatography-Mass Spectrometry and Gas Chromatography-Tandem Mass Spectrometry of Cyclic Fatty Acid Monomers Isolated from Heated Fats, J. Chromatogr. 562 659-672 (1991). 

Le Quere, J.-L., Sebedio, J.-L., Henry, R. et al. (1991) Gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry of cyclic fatty acid monomers isolated from heated fats. J. Chromatogr., 562, 659-72. 

Sebedio, J.-L., Prevost, J., Ribot, E. and Grandgirard, A. (1994) Utilization of high-performance liquid chromatography as an enrichment step for the determination of cyclic fatty acid monomers in heated fats and biological samples. J Chromatogr., 659, 101-9. 

If resin is to be introduced, the requisite proportion is to be thrown into the previously heated fat acid, and the stirring continued until the whole of the resin has melted, after which the fused sal-soda is to be run in as described. 

The oxidation of unsaturated fats is not only greatly accelerated at high temperatures, but the free radical mechanism is changed by the decrease in oxygen concentration in heated fats. At elevated temperatures, the oxygen availability is lower and becomes limiting (see Chapter 7.E). The alkyl radicals, formed by initiation (1), become more important because the rate of the oxygenation reaction (2) is diminished at elevated temperatures. The termina-... 

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