The lipid fraction

The membrane contains 0.5-1.0% of the total lipid in milk and is composed principally of phospholipids and neutral lipids in the approximate ratio 2 1, with lesser amounts of other lipids (Tables 3.9 and 3.10) contamination with core lipid is a major problem. The phospholipids are principally phosphatidylcholine, phosphatidylethanolamine and sphingomyelin in the approximate ratio 2 2 1. The principal fatty acids and their approximate percentages in the phospholipids are C14.0 (5%), Ci -o (25%), C,g.o (14%), C,g., (25%), Cig,2 (9%), 22 0 (3%) and 24,0 (3%). Thus, the membrane contains a significantly higher level of polyunsaturated fatty acids than milk 

Component mg 100 g fat globule mg m fat globule surface % (w/w) of total membrane 

GMi Galactosyl-A-acetylgalactosaminyl-(neuraminosyl)-galactosyl- glucosyl-ceramide 

GD3 (disialohematoside) Neuraminosyl-(2 - 8)-neuraminosyl-(2 - 3)-galactosyl-glucosyl-ceramide 

GDj N-Acetylgalactosaminyl-(neuraminosyl-neuraminosyl)- galactosyl-glucosyl-ceramide 

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Phosphatidylcholine is an important component of cell membranes but cell mem branes are more than simply lipid bilayers Although their composition varies with their source a typical membrane contains about equal amounts of lipid and protein and the amount of cholesterol m the lipid fraction can approximate that of phosphatidylcholine The lipid fraction is responsible for the structure of the membrane Phosphatidyl choline provides the bilayer that is the barrier between what is inside the cell and what IS outside Cholesterol intermingles with the phosphatidylcholine to confer an extra measure of rigidity to the membrane... 

Research in physiology carried out in the 1930s established that the lipid fraction of semen contains small amounts of substances that exert powerful effects on smooth mus cle Sheep prostate glands proved to be a convenient source of this material and yielded a mixture of structurally related substances referred to collectively as prostaglandins We now know that prostaglandins are present m almost all animal tissues where they carry out a variety of regulatory functions... 

The lipid fraction is responsible for the structure of the membrane. Phosphatidylcholine provides the bilayer that is the banier between what is inside the cell and what is outside. Cholesterol intermingles with the phosphatidylcholine to confer an extra measure of r-igidity to the membrane. 

No discussion of the use of biotransfarmation in lipid chemistry would be complete without some mention of chemical transformation relating to fatty adds. Fatty adds are a major component of the lipid fraction of organisms. They are mainly found as components of triglycerides and phospholipids, although they may occur in smaller quantities as free fatty adds or as esters of other moieties. Fatty adds, either as free adds or as esters, are valuable commodities in the food and cosmetics industries. They may also serve as precursors of a variety of other compounds. 

Isotachis lyallii Mitt, is a liverwort that occurs on both the north and south islands of New Zealand. A study of the lipid fraction of this species collected from both islands revealed different secondary metabolite profiles involving sesquiterpenes and aromatic esters (Asakawa et al., 1997). The sesquiterpene array consisted of... 

Those authors also demonstrated that neither sexual stage nor age of plant had any effect on the qualitative composition of the lipid fractions. They did comment, however, on the possibility that the secondary chemical output of plants at these different sites might reflect local environmental conditions, especially considering that the distance between the sites at Castelluccio and Brucoli is only a few kilometers. They pointed to the work of Howard et al. (1980), who had demonstrated such effects on the chemical content of two species of Laurencia in California over... 

After the extraction of lipid and nonlipid components from the leaves of mandarin orange Citrus reticulata, the lipid fraction was further separated by PTLC to determine different lipid classes that affect the chemical deterrence of C. reticulata to the leaf cutting ecat Acromyrmex octopinosus. These lipids seem to be less attractive to the ants [81a]. The metabolism of palmitate in the peripheral nerves of normal and Trembler mice was studied, and the polar lipid fraction purified by PTLC was used to determine the fatty acid composition. It was found that the fatty acid composition of the polar fraction was abnormal, correlating with the decreased overall palmitate elongation and severely decreased synthesis of saturated long-chain fatty acids (in mutant nerves) [81b]. 

There has not been found any substantial difference between the effects of irradiation on the lipid fraction of complex foods and that on model systems analogous to to fats. The autooxidation products of either natural fats or of model systems on irradiation are the same as those present in oxidized fats that... 

The ORAC assay proposed by Ou and others (2001) is limited to hydrophilic antioxidants because of the aqueous environment of the assay. However, lipophilic antioxidants play a critical role in biological defense systems. Huang and others (2002) expanded the assay to the lipidic fraction by introducing a randomly methylated 13-cyclodextrin (RMCD) as a water-solubility enhancer for lipophilic antioxidants. Various kinds of foods, including fruit juices and drinks, fruits, vegetables, nuts, and dried fruits, have been evaluated with this method (Zhou and Yu 2006 Wu and others 2004 Kevers and others 2007 Wang and Ballington 2007 Almeida and others 2008 Mullen and others 2007). 

Although the 100% extraction rate ensures a bigger yield, wholemeal is not particularly popular with millers as a stronger grist is needed. In addition, its shelf life is only three months (cf. a year for white flour). The reduction in shelf life is supposed to be caused by oxidation of the lipid fraction that is absent from white flour. Furthermore, wholemeal flour must be kept apart from white flour less that is contaminated. 

It is unknown which compounds are involved in Liolaemus communication. However, information available from the chemical composition of the lipidic fraction of the precloacal secretions suggests that individuals, populations and species can be discriminated by the chemical profile of these secretions (Escobar, Escobar, Labra and Niemeyer 2003 Escobar, Labra and Niemeyer 2001). This, in addition to probable chemical differences in the other sources of chemosignals, may allow individual, population and species recognition (Labra et al. 2001). Based on the individual variation observed in the composition of the secretions of L. bellii (Escobar et al. 2001), it is likely that lizards can achieve self-recognition, and also that they can extract detailed information about sender characteristics, as we have seen for L. monticola (Labra 2006). 

One advance in the area of LLE is the use of solid supports that facilitate the partitioning of the analyte(s) of interest. LLE extraction methods involving nonpolar matrices often suffer from the formation of emulsions, and using the solid support is a possible solution. In one study, polychlorinated biphenyls, dioxins, and furans were extracted from the lipid fraction of human blood plasma [32], using diatomaceous earth as the solid support. Long glass columns (30 cm) were packed with several layers of Chem-Elut (a Varian product) and sodium chloride. The plasma samples were diluted with water and ethanol and passed over the columns. A mixture of isopropanol and hexane (2 3) was passed over the column and the LLE was performed. It can be concluded that the LLE with the solid support is easier to perform and can be applied to other lipid heavy matrices such as milk [32]. 

In a primate, Microcebusmurinus Tiosimi3L) male odor depresses the level of plasma testosterone in other males. The lipid fraction (ether extract) of male... 

Retinoids The challenge in fat-soluble vitamins analysis is to separate them from the lipid fraction that contains interferents. Alkaline hydrolysis, followed by LLE, is widely applied to remove triglycerides. This technique converts the vitamin A ester to all-trani-retinol. A milder process, which does not hydrolyze vitamin A ester, is alcoholysis carried out with metha-nolic KOH solution under specific conditions that favor alcoholysis rather than saponification. A more accurate explanation of this technique is reported in the book Food Analysis by FIPLC [409]. For some kind of matrices a simple liquid extraction can be sufficient with [421-423] or without [424,425] the purification... 

Noguchi, S. Fujioka and A. Sakurai. Identification of teasterone and phytosterols in the lipid fraction from seeds of Cannabis sativa L. Nihon Yukagakkaishi 1997 46(12) 1499-1504. 

Soulier, and H. Cousse. Comparative study of the lipid fraction of pulp and seeds of Serenoa re pens (Palma-ceae). 01 Corps Gras Lipides 1996 3(2) 136-139. 

Lactones are minor constituents in pork fat compared to beef fat, but 5-decalactone was highly concentrated in the FI fraction of the 207 bar/50 C extract The furans, furanones and thiazoles were undoubtedly formed from Maillard reaction precursors and this type of volatQe would be more prevalent in the lipid fraction of cooked pork compared to pork fat alone. 

One of the primary reactions of ionizing radiation with saturated fatty acids is decarboxylation and alkane formation (2). Dimers tend to be produced by reaction of ionizing radiation with unsaturated fatty acids (2). When meats are irradiated C -C 7 n-alkanes, C2-C17 n-alkenes, and C4-Cg iso-alkanes are the predominant products from the lipid fraction (10), Irradiation of the lipoprotein fraction of meat results in the formation of the following volatile compounds Ci-C 7 n-alkanes, C2-C1J n-alkenes, dimethyl sulfide, benzene, and toluene (10). 

The guanidines, comprising dodine and guazatine, have long-chain alkyl groups and act as non-specific detergents. The lipophilic alkyl chain attaches to the lipid fraction of membranes whilst the polar guanidino portion remains in the aqueous phase. The result is a disruption in the membrane permeability characteristics and active transport systems. 

The hydrophobic section can associate with the lipid fraction and the cationic section with the ionic part of the phospholipids. 

Prior to phospholipid analysis, it is imperative to extract the lipids from their matrix and free them of any nonlipid contaminants. Phospholipids are generally contained within the lipid fraction, which may be recovered by the traditional Bligh and Dyer or Folch extraction procedure (9,22). In any phospholipid extraction method it is recommended to include a rather polar solvent in addition to a solvent with high solubility for lipids. The former is needed to break down lipid-protein complexes that prevent the extraction of the lipids in the organic phase. Traditionally, mixtures of chloroform and methanol (especially 2 1, v/v) have been recommended. These are washed with water or aqueous saline to remove nonlipid contaminants. Comparing the recovery of phospholipids, Shaikh found that the neutral phospholipids PC, PE, SPH as well as DPG were nearly quantitatively extracted by all solvent systems studied (Table 1), although Bligh and Dyer, in which the lower phase was removed only once, was somewhat worse (23). 

The lipid fraction of foods containing the fat-soluble vitamins is composed mainly of triglycerides, with much smaller amounts of sterols, carotenoids, phospholipids, and minor li-poidal constituents. All of these substances exhibit solubility properties similar to those of the fat-soluble vitamins, and therefore they constitute a potential source of interference. A proportion of the indigenous fat-soluble vitamin content of a food is bound up with a lipoprotein complex, and hence the fat-protein bonds must be broken in order to release the vitamin. The protective gelatin coating used in certain proprietary vitamin premixes will need to be dissolved before commencing the analysis of supplemented foods. 

Some methods of selectively extracting the lipid fraction from various foods prior to the determination of the fat-soluble vitamins by HPLC are discussed below. 

Full fat milk contains about 3% fat and triacylglycerols account for about 95% of the lipid fraction. Other components of the lipid fraction are diacylglycerols, cholesterol, phospholipids, and free fatty acids. The lipid structures contain many fatty acids from all major classes, that is, saturated, monounsaturated, and polyunsaturated fatty acids (Haug et al., 2007). More than 60% of the fatty acids in cow s milk and consequently in dairy products are saturated, including shorter and medium... 

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