Triglycerides structure, determination

Phospholipids, components of every cell membrane, are active determinants of membrane permeability. They are sources of energy, components of certain enzyme systems, and involved in lipid transport in plasma. Because of their polar nature, phospholipids can act as emulsifying agents. The structure of most phospholipids resembles that of triglycerides except that one fatty acid radical has been replaced by a radical derived limn phosphoric acid and a nitrogen base. c.g.. choline or serine. 

Solid Fat Index. This analysis has become the most important criterion for the melting behavior and crystalline structure of fats and oils products. It determines the proportion of solid and liquid materials at a given temperature. The solid fat index (SFI) analysis is an empirical measure of the solid fat content. It is calculated from the specific volume at various temperatures using a dilatometric scale graduated in units of milliliters times 1000. Values for the solid contents are usually determined at 50°F, 70°F, 80°F, 92°F, and 104°F or 10°C, 21.1°C, 26.7°C, 33.3°C, and 40°C. Unlike the tropical oils, cottonseed and the other oleic- and lino-leic-classification oils do not contain any significant quantity of triglycerides made up of two or three saturated fatty acids therefore, the solid fat index at the lowest temperature usually measured would have minimal values. Natural cottonseed oil can have a solid fat index content at 50°F or 10°C but not at the higher temperature measurements. 

Extraction Rates. The design of large-scale solvent extraction vessels must accommodate the rate at which equilibrium is attained between the free miscella flowing past the solid particles and the miscella absorbed within the solids. Attainment of equilibrium may be quite slow, particularly as the oil content of the solid material drops to low levels. Investigations show that the rate at which equilibrium is approached (in effect, the extraction rate) is influenced by many factors, including the intrinsic capacity for diffusion of solvent and oil, which is determined primarily by the viscosities of the two the size, the shape, and the internal structure of the solid particles and, at low oil levels in the solids, the rate at which the solvent dissolves nontriglyceride substances that are soluble but dissolve less readily than the triglycerides. 

Cholesterol, which is largely insoluble in aqueous m a, travels through the blood circulation in the form of Upoprotein complexes. The plasma lipoproteins are a family of globular particles that share common structural features. A core of hydrophobic lipid, principally triacylglycerols (triglycerides) and cholesterol esters, is surrounded by a hydrophilic monolayer of phospholipid and protein (the apolipoproteins) [1-3]. Lipid-apolipoprotein interactions, facihtated byi amphi-pathic protein helices that segregate polar from nonpolar surfaces [2,3], provide the mechanism by which cholesterol can circulate in a soluble form. In addition, the apolipoproteins modulate the activities of certain enzymes involved in Upoprotein metabolism and interact with specific cell surface receptors which take up Upopro-teins by receptor-mediated endocytosis. Differences in the Upid and apoUpoprotein compositions of plasma Upoproteins determine their target sites and classification based on buoyant density. 

In this chapter we will study the chemistry of lipids with a wide variety of structures and biological functions. Among these are the triglycerides that stock our adipose tissue, pain-producing prostaglandins, and steroids that determine our secondary sexual characteristics. 

Determine whether each structure is a fatty acid, triglyceride, phosphohpid, steroid, or wax. Explain your reasoning. 

The stable crystal form of triglycerides exhibits the triclinic chain packing Tjl, and this subcell structure was first determined by Vand and Bell (1951). The subcell contains two CH2 groups related by a centre of symmetry. The dimension in the case of n-octa-decane (Nyburg and Liith, 1970) is a = 4.285 A, b = 5.414 A, c = 2.539 A, a = 80.99°, = 112.2°... 

The H-RMN spectrum given in Fig. 3.7 had all the resonances expected for the CO structure, viz. 3-hydroxy groups and 3 insaturations per triglyceride molecule. Additionally, elemental analyses and molecular weight determination confirmed the proposed structure. 

The chromatogram-like structure of the carbonyl region shows separation of a mixture from different mono-, di- and triglycerides and free fatty acids (Fig. 4.7). This method is used for quality control of olive oils (Sacchi et al, 1990). Integrals of the respective intensities are directly proportional to the molar amount of the component, with one restriction comparison is only allowed between atoms in the same chemical environment, for example carbonyls only with carbonyls, methyls only with methyls and so on. There is no need for a standard to evaluate the fatty acid distribution, and no calibration and no quality control samples are needed. No chemical modification such as saponification or derivatization is necessary, so degradation of the chemically sensitive polyunsaturated acids is avoided. The material can be recovered unchanged after the measurement. In addition to the general fatty acid distribution a determination of individual distributions is possible. ... 

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