Composition of lipid classes

ACYL AND ALKYL COMPOSITION OF LIPID CLASSES DETERMINATION OF FATTY ACIDS... 

Bianchi, G. and Vlahov, G. (1994) Composition of lipid classes in the morphologically different parts of the olive fruit, cv. Coratina (Olea europaea Linn.). FatSci. Technol., 96, 72-77. 

Sanders, T.H. (1980b) Fatty acid composition of lipid classes in oils from peanuts differing in variety and maturity. J. Am. Oil Chem. Soc., 57, 12-15. 

Figure 1. Fatty acid composition of lipid classes from tissues of mature seeds with spotted cotyledons.

The composition of lipids from the silk and cuticule has been reviewed by Schulz (1997a, 1999). These lipids consist primarily of alkanes, as found in other arthropods, with 2-methylalkanes with an even number of carbon atoms in the chain being most abundant, with lesser amounts of alcohols, acids, aldehydes, and wax esters. Recently, a thorough analysis of the silk lipids of N. clavipes (Schulz, 2001) revealed a unique class of lipids from spider silk and cuticle, consisting of straight-chain and branched methyl ethers (1-methoxyalkanes, Fig. 4.4) with chain lengths between 25 and 45 carbon atoms. 

Accurate determination of lipids in foods is required for nutritional labeling, certification, or for evaluation of standard of identity and uniformity, as well as examination of their effects on functional and nutritional properties of foods. Following lipid extraction and precise quantitative analysis, lipids so obtained may be used for analysis of other lipid characteristics and properties provided that nondestructive and mild extraction procedures are employed that retain the integrity of lipids. Thus, determination of lipid classes, fatty acid composition (unit du), and oxidative state of lipids (Chapter D2), amongst others, may be pursued following the extraction process. 

NU Olsson, AJ Harding, C Harper, N Salem Jr. High performance liquid chromatography method with light scattering detection for measurements of lipid class composition analysis of brains from alcoholics. J Chromatogr B 681 213—218, 1996. 

The fatty acid composition of lipids is usually analyzed by gas chromatography following transesterification into methyl esters. Unmodified lipids can be analyzed by HPLC or by soft chemical ionization mass spectrometry. In the course of sample preparation it is often necessary to separate the various membrane fractions (plasma membrane, thylakoid, microsomal, mitochondrial, etc.) by sophisticated gradient centrifugations, as well as the individual lipid classes within a membrane fraction, usually by thin-layer chromatography (TLC). 

Rouser G, Yamamoto A. Kiitchevsky G. Cellular membranes. Structure and regulation of lipid class composition species differences, changes with age and variations in some pathological states. Arch Intern Med 1971 127 1105-1121. 

Total lipid extracts from natural or food sources are likely to contain a diverse mixture of lipid classes. While one or two lipid classes may dominate on a proportional basis, it can often be the amount or composition of minor lipid classes that are of particular interest. Conversely, the presence of minor lipid classes can interfere... 

ITigh-performance liquid chromatography (FIPLC) is routinely used for the compositional analysis of lipid classes, TAGs, and tocopherols. Flowever, there can be problems for the quantitative detection of lipids other than tocopherols because most lipids do not have a suitable chromaphore, and therefore cannot be detected spectrophotometrically. Evaporative technology such as nebulizing mass detectors and the quartz/flame ionization transport system has to be employed. 

Table 1.3 summarizes recent and important oceanographic and limnological work based on the analysis of lipid class composition by TLC-FID. A notable characteristic of this compilation of studies is the broad spectrum of matrices analysed, from lipids in environmental samples of water, sediments, soils and micro-organisms to vertebrates. 

Oshima, T. and Ackman, R. G. (1991) New developments in Chromarod/Iatroscan TLC-FID analysis of lipid class composition. Journal of Planar Chromatography, 4, 27-34. 

CHEN G Q, JIANG Y and CHEN F (2008) Variation of lipid class composition in Nitzschia laevis as a response to growth temperature change. Food Chemistry, 109,88-94. 

The currently accepted structure of B. is the fluid mosaic model. Lipid molecules and membrane proteins are free to diffuse laterally and to spin within the bilayer in which they are located. However, a flip-flop motion from the inner to the outer surface, or vice versa, is energetically unfavorable, because it would require movement of hydrophilic substituents through the hydrophobic phase. Hence this type of motion is almost never displayed by proteins, and it occurs much less readily than translational motion in the case of lipids. Since there is little movement of material between the inner and outer layers of the bilayer, the two faces of the B. can have different compositions. For membrane proteins, this asymmetry is absolute, and, at least in the plasma membrane, different proportions of lipid classes exist in the two monolayers. Attached carbohydrate residues appear to be located only on the noncytosolic surface. Carbohydrate groups extending from the B. participate in cell recognition, cell adhesion, possibly in intercellular communication, and they also contribute to the distinct immunological character of the cell. 

An abnormal lipoprotein was once defined according to the following criteria inap-propritate lipid composition of density class (by this way the beta-VLDL of type III hyperlipoproteinemia was detected) or unusual protein content of density class (LP (a)). Both criteria led to the detection of lipoprotein X (LP-X). 

Ohshima, T Ackman, R.G. New developments in chromarod/iatroscan TLC-FID Analysis of lipid class composition. J. Planar Chromatogr. 1991, 4, 27—34. 

There are a number of books available that deal with lipids and their structures, and the author has found those cited to be of particular value [319,367]. Literally thousands of papers have appeared over the last 25 years detailing the structures and compositions of lipids from particular tissues and species, as determined by modem chromatographic methods, but there appears to have been very little effort to collate and critically compare these data in any systematic way, or to relate the compositions of lipids to their functions. Among other consequences of this, there remain anomalies and gaps in our knowledge. Comprehensive accounts of the lipids of the tissues of ruminant animals [162], tissue and membrane phospholipid compositions [395,970] and triacylglycerol compositions [125,553,686,824] have appeared, however, and there are miscellaneous reviews of the compositions of specific lipid classes or tissues in the literature. The author recently attempted to summarise the essential features of lipid composition in a succinct manner [168]. This cannot be repeated here, and a brief summary only of lipid structure and composition follows. 

As an increasing number of reports appear on the subject of low temperature acclimation in plants, it becomes more and more apparent that a variety of lipid compositional changes are effected. The principal ones include 1) altered levels of fatty acid unsaturation, 2) altered molecular species composition within lipid classes, and 3) altered proportions of the different lipid classes. These three categories of change will be discussed separately. 

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