Beef triacylglycerol

Hu X, Jandacek RJ and White WS. 2000. Intestinal absortion of (3-carotene ingested with a meal rich in sunflower oil or beef tallow postprandial appearance in triacylglycerol-rich lipoproteins in women. Am J Clin Nutr 71 1170-1180. 

This subject is discussed in Chapter 15, but a brief summary is given here, as an introduction to fat metabolism. The three major components of a human diet are meat, fish and plants, and the fats associated with each component can be different. Meat usually comprises the muscle of mammals and birds but it is always associated with fat. Even apparently lean meat may have a high fat content a 250 g beef steak may contain 60 g fat in addition to its 80 g protein. Some of this will be adipose tissue between muscles the remainder is triacylglycerol (TAG) within the fibre. In addition, milk and other dairy products contain significant amounts of fat about a quarter of the fat in the average UK diet comes from dairy produce. 

Triacylglycerols (fats and oils) store the majority of the energy in most animals and plants. Fats such as beef tallow remain solid or semisolid at room temperature while oils such as olive oil or corn oil are liquid at that temperature. Oils solidify only at lower temperatures—in a refrigerator, for example. The different kinds of fatty acids found in the side chains of the triacylglycerol cause the different melting temperatures. The fatty acids of oils contain more double bonds than do those of fats. 

From the 50% solid fat line in the isosolid diagram of physical blends of milk fat and beef tallow, it was evident that there were eutectic and compound interactions but these were absent in interesterified blends with a more complex triacylglycerol composition (Timms, 1979). 

Triacylglycerol profiles, determined by high-performance liquid chromatography (HPLC), may also be a tool for the detection of the adulteration of pork by beef fat (44). The presence of 5% or more of pork fat in beef or mutton tallow can be detected and quantified by HPLC analysis of fatty acids in the sn-2 position of the triacylglycerols, because the ratio of 16 0/18 loo9 at this position is about 5.0... 

Lipids constitute below 1% of the weight of fruits, vegetables, and lean fish 3.5% of milk 6% of beef 32% of egg yolk and 85% of butter. The lipids contained in the food raw materials in low quantities serve mainly as components of protein-phospholipid membranes and perform metabolic functions. In fatty commodities the majority of the lipids are stored as depot fat in the form of triacylglycerols. The lipids of numerous food fishes, such as orange roughy, mullets, codfish, and sharks,... 

Problem 19.64. Triacylglycerol A contains 53 percent oleic acid, 29 percent linoleic acid, 9 percent palmitic acid, 4 percent stearic acid, 1 percent myristic, and lesser amounts of other fatty acids. Triacylglycerol B contains 39 percent oleic acid, 29 percent palmitic acid, 24 percent stearic acid, 3 percent myristic, 2 percent linoleic, and lesser amounts of other fatty acids. One of the samples is peanut oil and the other is beef fat (tallow). Which is which ... 

Ans. Triacylglycerol A is peanut oil since it contains 84 percent unsaturated fatty acids (oleic + linoleic). Triacylglycerol B is beef fat since it contains only 41 percent unsaturated fatty acids (oleic + linoleic). 

Stearic add n-octadecanoic add, CH3-(CH2)](-COOH, a fatty acid, M, 284.5, m.p. 71.5°C, b.p.,5 232°C. Together with palmitic acid, S.a. is one of the most plentiful and most widely distributed fatty acids, occurring esterified in practically all animal and plant oils and fats, e.g. 34% in cocoa butter, 30% in mutton fat, 18% in beef fat, 5-15% in milk fat. It is used in the manufacture of candles, soaps, detergent antifoams, pharmaceuticals and cosmetics. Stearin is the triacylglycerol of S. a. 

The lipids in lean beef consist of about 2 to 4% triacylglycerols and 0.8 to 1% phospholipids containing 44% polyunsaturated fatty acids, which are mainly subject to oxidation. Oxidation occurs initially in the phospholipids of ceUular and subcellular membranes, which are in close proximity to the heme catalysts of the mitochondria and microsomes. A typical fatty acid composition of beef membrane phospholipids includes 22% 18 2,2% 18 3,15% 20 4, less than 1% 20 5 and 2% 22 6. Phosphatidylethanolamine is the main phospholipid implicated in lipid oxidation of cooked meat. Chicken and turkey muscle are more susceptible to oxidation than beef, because of their higher polyunsaturated phospholipid fraction and relatively low levels of natural tocopherols. Red poultry muscles oxidize faster than white because of higher phospholipid and iron contents. 

Hydroxylated triacylglycerols from castor oil and beef tallow were separated according to their equivalent carbon number (ECN) using a 35°C Cig column (RI... 

The fatty acid composition of beef fat (Table 14.3) is not influenced greatly by feed intake, but that of hog fat (lard) is. The composition of edible beef fat triacylglycerols is given in 3.3.1.4. The following commercial products are prepared from beef fat Prime Beef Fat ( premier jus ) is obtained by melting fresh and selected fat trimmings in water heated to 50-55 °C. The acid value resulting from lipolytic action (cf. 14.5.3.1)... 

In contrast to the composition of triacylglycerols found in beef fat (Table 3.13), lard contains fewer triacylglycerols of the type SSS and more of the types SUU, USU and UUU (S = saturated U = unsaturated fatty acid). As a consequence, lard melts at lower temperatures and over a range of temperatures rather than sharply at a single temperature, and its shelf life is not particularly long. In comparison with beef, pig depot fat... 

Fats can be hard and brittle substances (cocoa butter), hard substance (beef tallow), gooey soHds (pork lard, pahn oil) and viscous Hquids (vegetable oils). The melting and soHdihcation points of some fats are Hsted in Table 3.27. The range of values is mainly related to the variabihty of the composition of fatty acids and triacylglycerols. 

Coconut and pahn kernel oil, pahn oil, traditional rapeseed oil and cottonseed oil, beef tallow and butter tend to preferentially crystallise in the metastabile 3 -modification, which has characteristic small needle-Hke crystals. These triacylglycerols characteristically form clusters and aggregates to form the crystal spatial network, ideally they form a gel structure, which shows thixotropy. Fats... 

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