Total lipid fraction

Silica columns can tolerate relatively heavy loads of triglyceride and other nonpolar material. Such material is not strongly adsorbed and can easily be washed from the column with 25% diethyl ether in hexane after a series of analyses (83). Procedures for determining vitamins A and E have been devised in which the total lipid fraction of the food sample is extracted with a non-aqueous solvent, and any polar material that might be present is removed. An aliquot of the nonpolar lipid extract containing these vitamins is then injected into the liquid chromatograph without further purification. Direct injection of the lipid extract is possible because the lipoidal material is dissolved in a nonpolar solvent that is compatible with the predominantly nonpolar mobile phase. Procedures based on this technique are rapid and simple, because there is no need to saponify the sample. 

Infant formula Disperse sample in nonaqueous solvent mixture (DMSO/DMF/ CHC13, 2 + 2+1) containing 0.1% (w/v) ascorbic acid. Partition total lipid fraction into hexane, centrifuge. Radial-PAK cartridge containing Resolve silica 5 /xm... 

Significant activity of the total lipid fraction of Carthamus lanatus was found against Staphylococcus aureus [249]. The lipid composition was examined and almost equal amounts of triacylglycerols, digalactosyl diacylglycerols and phospholipids were determined. Examples of other antimicrobial lipids from the Anthemideae tribe also included Xanthium strumarium lipids [250], and glyceroglycolipids from Serratula... 

Steroid Analysis. Steroid analysis was carried out on selected humic and fulvic freeze-dried samples of stream, foam, and foam extract from the Suwannee River by Microbial Insights, Inc., (Knoxville, TN). Tri-methyl silyl derivatives of 3 P ol sterols were prepared from either the neutral lipid or total lipid fraction by alkaline saponification as described by Nichols et al. (23). 

Figure 11-1 a Variation in the ratio of sphingomyelin (S) to phosphatidylcholine (PC) and other constituents such as cholesterol (C) and phosphatidylethanolamine (PE) in the total lipid fraction of Erythrocytes from various species, b Sphingomyelin relative to total lipids present in the endoplasmic reticulum (reproduced from [2] with permission from the Macmillan Press Ltd, London. 

An example is given for the composition of the liver cell membrane [2], There is also a considerable difference in the proportion of phospholipids in different cell types and different species. Figure 11-1 shows the variation of sphingomyelin (S) lo phosphatidylcholine (PC) content in the total lipid fraction of erythrocytes from various species and of ox endoplasmic reticulum in various organs [2], The lateral mobility of lipids in membranes is another essential aspect [7],... 

Only a small portion of the total lipid fraction obtained by extraction with a nonpolar solvent consists of long-chain carboxylic acids. Most of the carboxylic acids of biological origin are found as esters of glycerol, that is, as triacylglycerols (Fig. 23.1). ... 

Saponification of the extracts is generally desirable to remove unwanted lipid materials. However, this step is omitted in the isolation of carotenol esters, since these are hydrolyzed by this procedure. It is also omitted in the isolation of carotenoids such as fucoxanthin and peridinin, which are alkali-labile. If acetone has been used in the initial extraction, it is essential that all traces be removed before saponification. The general procedure used involves dissolving the total lipid fraction in an alcoholic (ethanol or methanol) solution of potassium hydroxide. The mixture is then either heated for a short period of time while kept in the dark, or left in the dark at room temperature for 12-16 h. There has been considerable discussion of the merits of these two procedures. Which method is used is dependent on the nature of the samples being analyzed and the requirements of the analysis (Davies, 1976 Liaaen-Jensen, 1971). After saponification, water is added, and neutral lipids (the unsaponifiable fraction) are extracted with diethyl ether or hexane. Acidic carotenoids remain in the alkaline phase and are extracted with diethyl ether or hexane after acidification with acetic acid. The unsaponifiable fraction usually contains sterols as well as carotenoids. If desired, sterol contaminants can be removed by precipitation from cold (- 10°C) petroleum ether or by precipitation of these compounds as their digitonides. 

Total phospholipids expressed in % ofthe total lipid fraction, tr = trace. 

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