Lipids acylglycerols

Wanasundara et al. (1999) reported that neutral lipids (acylglycerols and fatty acids) constitute 96% of the total lipid in flaxseed, whereas polar lipids (glycolipids and phospholipids) account for 1.4%. Stenberg et al. (2005) observed similar findings except that less phospholipid was detected. Froment et al. (1999) discussed the effects of cultivar, location, and late harvest on phospholipid content. Neutral lipid fraction of flaxseed meal was 95-98% triacylglycerols (TAG) and thus accounts for the predominant lipid in flaxseed (Oomah et al., 1996). 

In some polysaccharides, the reducing terminal is linked, through a phosphoric diester linkage, to O-1 of a 2,3-di-6 -acylglycerol. This structural feature has been demonstrated for some capsular polysaccharides from E. coli and Neisseria species, - but is probably more common than that. Non-covalent linkage between the lipid part and the cell membrane may explain why extracellular polysaccharides often occur as capsules, and the high (apparent) molecular weight observed for these polysaccharides may be due to micelle formation in aqueous solution. 

Because they are uncharged, acylglycerols (glycerides), cholesterol, and cholesteryl esters are termed neutral lipids. 

Hypolipoproteinemias Abetaiipoproteinemia No chylomicrons, VLDL, or LDL are formed because of defect in the loading of apo B with lipid. Rare blood acylglycerols low intestine and liver accumulate acylglycerols. Intestinal malabsorption. Early death avoidable by administration of large doses of fat-soluble vitamins, particularly vitamin E. 

Besides water, the diet must provide metabolic fuels (mainly carbohydrates and lipids), protein (for growth and turnover of tissue proteins), fiber (for roughage), minerals (elements with specific metabolic functions), and vitamins and essential fatty acids (organic compounds needed in small amounts for essential metabolic and physiologic functions). The polysaccharides, tri-acylglycerols, and proteins that make up the bulk of the diet must be hydrolyzed to their constituent monosaccharides, fatty acids, and amino acids, respectively, before absorption and utilization. Minerals and vitamins must be released from the complex matrix of food before they can be absorbed and utifized. 

Lipids may be defined as a large group of molecules with a substantial portion of aliphatic or aromatic hydrocarbon. Included are molecules with diverse chemical characteristics, such as the hydrocarbons, soaps, detergents, acylglycerols, steroids, phospholipids, sphin-golipids, and fat-soluble vitamins, and, subsequently, with diverse physical behavior. One of the most important characteristics of lipids from a biological aspect is their behavior in aqueous environments, as all cells exist in an aqueous milieu. In this respect, the lipids range from almost total insolubility to nearly complete solubility. 

The potential for the preservation of lipids is relatively high since by definition they are hydrophobic and not susceptible to hydrolysis by water, unlike most amino acids and DNA. A wide range of fatty acids, sterols, acylglycerols, and wax esters have been identified in visible surface debris on pottery fragments or as residues absorbed into the permeable ceramic matrix. Isolation of lipids from these matrices is achieved by solvent extraction of powdered samples and analysis is often by the powerful and sensitive technique of combined gas chromatography-mass spectrometry (GC-MS see Section 8.4). This approach has been successfully used for the identification of ancient lipid residues, contributing to the study of artifact... 

Lipids are substances of biological origin that are soluble in non-polar solvents. There are saponifiable lipids, such as acylglycerols (fats and oils), waxes and phospholipids, as well as non-saponifiable compounds, principally steroids. 

Kaneko E, Polymorphism and phase transitions of fatty acids and acylglycerols, in Crystallization Processes in Fats and Lipid Systems, Garti N. and Sato K., eds., Marcel Dekker, New York, 2001, 53-97. 

Jensen, R.G. 1983. Detection and determination of lipase (acylglycerol hydrolase) activity from various sources. Lipids 18 650-657. 

Riederer (1990) published a more complex method based on two lipid-like compartments, an acylglycerol lipid compartment and a cuticle compartment. The acylglycerol-air partition coefficient was assumed to equal Kow/Kaw, while measured values of the cuticle-water partition coefficient were employed for the cuticle compartment. Riederer (1995) later modified this model to include a predictive equation for the cuticle-water partition coefficient, based on Kerler and Schonherr s measurements (1988) of eight chemicals with log KqW values ranging from 1.92 to 7.86. They used isolated citrus and rubber plant leaf cuticles as well as tomato and green pepper fruit cuticles. The resulting equation is... 

Other extraction methods used in the lipid extraction include supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE). With SEE, good extraction yields have been obtained for nonpolar lipids including ester-ified fatty acids, acylglycerols, and unsaponifiable matter. However, complex polar lipids are only sparingly soluble in supercritical carbon dioxide alone and polar modifiers, such as methanol, ethanol, or even water is required to improve the extraction of polar lipids (10). SFE has been used for the extraction of lipids especially from various food matrices, such as different nuts, edible oils, and seeds (11). The recoveries of lipids in SFE were on the same levels than with conventional solvent extraction methods (12,13), no significant differences between the fatty acids extracted were observed. PLE has also been used in lipid extraction, although only in very few applications (14). The elevated temperatures used in PLE can cause alteration of the lipid composition. 

CRABP-GST is immobilized onto a glutathione-containing resin at a concentration that saturates the resin. A complex lipid mixture was prepared by combining a concentrated lipid extract derived from mouse tissue (brain) [5] (DMSO stock) with exogenously added retinoic acid (RA, positive control) and 13C-oleic acid (negative control). Analysis of this complex lipid mixture by LC-MS prior to incubation with immobilized CRABP demonstrated that the mixture contained RA (added), phospholipids, acylglycerols, cholesterol esters, and cholesterol. A portion of this mixture (corresponding to 1 nmol of RA) was added to PBS (DMSO concentration should not exceed 5%) and incubated with the CRABP-GST bound beads for 1 h. 

Itabashi, Y. and Takagi, T. (1986) High performance liquid chromatographic separation of mono-acylglycerol enantiomers on a chiral stationary phase. Lipids, 21, 413-416. 

Uzawa, H., Noguchi, T., Nishida, Y., Ohrai, H., and Meguro, H. 1993. Determination of the lipase stereospecificities using circular dichroism (CD) lipases produce chiral di-O-acylglycerols from achiral tri-O-acylglycerols Biochim. Biophys. Acta(-Lipids and Lipid Metabolism), 1168, 253-260. 

Lipids are made up of many classes of very different molecules that all show solubility properties in organic solvents. Mass spectrometry plays a key role in the biochemistry of lipids. Indeed, mass spectrometry allows not only the detection and determination of the structure of these molecules but also their quantification. For practical reasons, only the fatty acids, acylglycerols and bile acids are discussed here, although other types of lipids such as phospholipids, [253-256] steroids, [257-259] prostaglandins, [260] ceramides, [261,262] sphingolipids [263,264] and leukotrienes [265,266] have been analysed successfully by mass spectrometry. Moreover, the described methods will be limited to those that are based only on mass spectrometry, even if the majority of these methods generally are coupled directly or indirectly with separation techniques such as GC or HPLC. A book on the mass spectrometry of lipids was published in 1993. [267]... 

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