Polyunsaturated fatty acid triacylglycerols

Polyunsaturated fatty acids Triacylglycerols containing primarily fatty acids with more than one double-bond are referred to as polyunsaturated fats. The effects of polyunsaturated fatty acids on cardiovascular disease is influenced by the location of the double bonds within the molecule. 

Saturated fatty acids do not contain double bonds in the hydrocarbon chain. Unsaturated fatty acids contain from one to hve double bonds. Those with one double bond are known as monounsaturated, those with two as diunsatu-rated and those with more than two as polyunsaturated fatty acids. A brief summary of the roles of saturated and unsaturated fatty acids is given in Table 11.1. The proportion of these fatty acids in triacylglycerol in human adipose tissue is presented in Table 11.2. 

Consumption of fats containing n-6 polyunsaturated fatty acids lowers plasma LDLs, but HDLs, which protect against coronary heart disease, are also lowered. Dietary n-3 polyunsaturated fats have little effect on plasma HDL or LDL levels, but they suppress cardiac arrhythmias and reduce serum triacylglycerols, decrease the tendency to thrombosis, and substantially reduce the risk of cardiovascular mortality. 

Lipids are susceptible to oxidation and, therefore, analytical protocols are required to measure their quality. Not all lipids have the same degree of susceptibility to oxidation. Many factors are responsible for a lipid s tendency to oxidize, including the presence of catalysts, oxidative enzymes, radiation, and a lipid-air interface, as well as the oxygen partial pressure, the incorporation of oxygen into the product, and the presence of metal ions. The most important factor is the degree of unsaturation of the lipid itself. The majority of a food product s polyunsaturated fatty acids (PUFAs) are generally contained in phospholipids, which are consequently more prone to autoxi-dation than the triacylglycerol fraction. 

Full fat milk contains about 3% fat and triacylglycerols account for about 95% of the lipid fraction. Other components of the lipid fraction are diacylglycerols, cholesterol, phospholipids, and free fatty acids. The lipid structures contain many fatty acids from all major classes, that is, saturated, monounsaturated, and polyunsaturated fatty acids (Haug et al., 2007). More than 60% of the fatty acids in cow s milk and consequently in dairy products are saturated, including shorter and medium... 

Myher, J.J., Kuksis, A., Gehr, K., Park, P.W. and DiersenSchade, D.A. (1996) Stereospecific analysis of triacylglycerols rich in long-chain polyunsaturated fatty acids. Lipids, 31, 207—215. 

The positional distribution of fatty acids in phosphatidylcholine and phosphatidylethanolamine, the major glycerophospholipids, of bovine milk, were investigated by Morrison et al. (1965) and are shown in Table 1.13. Unlike triacylglycerols, phospholipids do not contain short-chain fatty acids (14 0 being the shortest chain fatty acid present at a significant level). This is probably due to differences in the route of synthesis, as most short-chain fatty acids are found at the sn-3 position of triacylglycerols, which in phospholipids is occupied by the phosphate moiety. In phospholipids, the polyunsaturated fatty acids tend to be esterified preferentially at the sn-2 position, while the saturated fatty acids show a preference for the sn-1 position (Table 1.13). For phosphatidylethanolamine, 18 2 and 18 3 are found predominantly at the sn-2 position, while 18 1 is fairly evenly distributed and 16 0 and 18 0 are predominantly at the sn-1 position. In phosphatidylcholine, which is more saturated than phosphatidylethanolamine, the distribution of saturated and unsaturated fatty acids is less distinct between... 

The major differences between the lipids of bovine and human milk are in fatty acid composition and triacylglycerol structure. Bovine milk contains substantial quantities of C4 o-Ci0 o, about 2% Cis 2 and almost no other long-chain polyunsaturated fatty acids. The fatty acid composition is not altered by ordinary changes in diet. Human milk contains very little C4 o-C10 o, 10-14%i (w/w of fat) Ci8 2, and small quantities of other polyunsaturates. The triacylglycerol structure differs, with much of the sn-2 position in human milk lipids occupied by C16 0 and the sn-2 position of bovine milk-fat occupied by C4 o-Ci0 o-... 

Haraldsson, G. G. 2005. Structured triacylglycerols comprising omega-3 polyunsaturated fatty acids. In Hou, C. T. (Ed.), Biocatalysis and Biotechnology for Functional Foods and Industrial Products (pp. 18-1-18.21). Boca Raton FL CRC Taylor and Francis. 

In the menhaden oil winterization of Table 6, the increase in polyunsaturated fatty acids is modest in the olein fraction, and the commercial objective may have been the stearine fraction, 50% richer in saturated acids of commercial interest. As already remarked for polyunsaturated fatty acids, 18/12 (in implied percents) or 180/120 (in mg/g) were obtained as triacylglycerols from menhaden and/or anchovy oils with minimal trouble and technology. Retail product No. 2 is also a product like No. 5. Winterization also would prevent either capsules or oil turning cloudy if refrigerated. Strangely, hardly anybody challenges label claims as to chemical nature, although the word oil may be carelessly used because concentrates are almost always ethyl esters, but numbers should always be expressed in the free acid form. 

Although polyunsaturated fatty acids are biohydrogenated to stearic acid (Cl8 0) in the rumen, they are desaturated to oleic acid in the small intestine, mucosa adipose tissue, and mammary gland. Thus the ratio of C18 l to C18 0 is greater in the fatty tissue and the milk lipids than in plasma triacylglycerols. Ruminant milk also contains 40-50% C4 0-C14 0 fatty acids by weight synthesized in the mammary glands from acetate (52). 

Fats not protected for escape or bypass will be altered if fed to ruminants. Within limits, triacylglycerols are hydrolyzed, and the polyunsaturated fatty acids are biohydrogenated by rumen bacteria enzymes. 

Polyunsaturated and oxygenated fatty acids, obtained from triacylglycerols (TAG) of several different plant and animal species, are valuable materials feedstock for value-added products in a variety of industries food, pharmaceutical, cosmetics, and paints and coatings. The acyl species, their chemical structure, and their most abundant sources are summarized in Table 1. In contrast to inexpensive Cie and Cig saturated and A9-unsaturated acyl groups, such as palmitic (16 0), stearic (18 0), oleic (18 l-9c), linoleic (18 2-9c, 12c), and a-linolenic acid (ALA 18 3-9c, 12c,15c), recovered from the oil of soybean and other common sources, and C4-C16 saturates from palm oil and milk fat, polyunsaturated and oxygenated acids are derived from less common sources, and particularly for polyunsaturated fatty acid (PUFA), are typically present at only 20 0% purity. 

Yamane, T. Lipase-catalyzed synthesis of structured triacylglycerols containing polyunsaturated fatty acids monitoring the reaction and increasing the yield. In Enzymes in Lipid Modification Bornscheuer, U.T., Ed. Wiley-VCH Weinheim, Germany, 2000 148-169. 

The amount of VLDL secreted by the liver is extremely variable and can be affected in a number of ways. A primary determinant of VLDL output is the flux of free fatty acids entering the liver. The liver responds to an increase in free fatty acids by synthesis of more and larger VLDLs. If saturated fatty acids predominate in the formation of triacylglycerol, the VLDL particles will be more numerous but smaller than if polyunsaturated fatty acids predominate. This finding may be related to the reduction in plasma cholesterol levels that results from elevating the proportion of polyunsaturated fats in the diet. The surface-to-volume ratio is smaller in the larger VLDLs. Since cholesterol... 

The substrate for the reaction is triacylglycerol of polyunsaturated fatty acid, which is not soluble in water, but can be solubilized with high concentration in octane. The lipase converts its substrate at the interface between octane and the aqueous phase. The free fatty acid produced is poorly water soluble. 

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