Lipid materials

Gel permeation ehromatography (GPC)/normal-phase HPLC was used by Brown-Thomas et al. (35) to determine fat-soluble vitamins in standard referenee material (SRM) samples of a fortified eoeonut oil (SRM 1563) and a eod liver oil (SRM 1588). The on-line GPC/normal-phase proeedure eliminated the long and laborious extraetion proeedure of isolating vitamins from the oil matrix. In faet, the GPC step permits the elimination of the lipid materials prior to the HPLC analysis. The HPLC eolumns used for the vitamin determinations were a 10 p.m polystyrene/divinylbenzene gel eolumn and a semipreparative aminoeyano eolumn, with hexane, methylene ehloride and methyl tert-butyl ether being employed as solvent. 

Figure 10.9 shows the ehromatograms of fortified eoeonut oil obtained by using (a) normal-phase HPLC and (b) GPC/normal-phase HPLC. As ean be seen from these figures, ehemieal interferenees due to lipid material in the oil were eliminated by using the MD system that was used for quantitative analysis of all of the eom-pounds, exeept DL-a-toeopheryl aeetate, where the latter was eo-eluted with a triglieeride eompound and needed further separation. 

Simple lipids such as CE, WE, EFA, cholesterol, alcohols, ketones, TG, DG, and MG are usually separated on silica gel plates. Depending on the complexity of the lipid material and the variety of lipid classes present in a single sample, either single-or multiple-solvent systems can be used (Figure 12.4a). Although benzene [45] or... 

The iodine number is an indication of the degree of unsaturation of triglycerides, and is the amount of iodine (in mg) required to react with 1 g of lipid material. 

Betulin and lupeol, together with low amounts of lupenone, betulone and betulinic acid, are characteristic of birch bark [87,153 157]. All these compounds are pentacyclic triterpenoids with a lupane skeleton. In addition to triterpenoids, birch bark contains high amounts of a lipid material, called suberin [158]. 

Direct Mass Spectrometry to Characterise Wax and Lipid Materials... 

Lipids represent a remarkable class among the organic substances found in archaeological remains and works of art. They can derive from many sources, including vegetable oils, animal lipids, and waxes, and they have been used in many different ways in art and everyday activities. Lipid materials have been used extensively by ancient and modern populations as food, illuminants, waterproofing materials, binders, ingredients in medicines, cosmetics and balms. 

Many analytical procedures based on GC/MS have been described for the analysis of a wide range of lipid materials in samples from art and historical objects [2,3,7,11,17,21,26], Wet chemical pretreatments are generally needed before GC/MS analysis, in order to ... 

Identifying a specific natural source of lipids after GC/MS analysis is not always straightforward. The occurrence of mixtures, the unspecific FA composition of many lipid materials, the fact that materials may be physically handled during pretreatment before use and the deep changes induced by ageing, mean that extreme caution is required when interpreting FA profiles. 

Sterols are seldom detected in archaeological residues due to their low concentration and the tendency to undergo chemical degradation. In any case, the presence of sterols or of their oxidation products in a sample can help distinguish between animal and plant lipid materials cholesterol is the most abundant animal sterol, while campesterol and sitosterol are the two major plant ones. 

The following subsections describe some case studies dealing with GC/MS procedures used to investigate lipid materials in archaeological objects and paintings. 

G. Chiavari, D. Fabbri and S. Prati, In situ pyrolysis and silylation for analysis of lipid materials used in paint layers, Chromatographia, 53, 311 314 (2001). 

Surfactants have been explored widely for their effects on drug absorption, in particular using experimental animals (Gibaldi and Feldman, 1970 Gibaldi, 1976). Surfactants alter dissolution rates (of lipid materials), surface areas of particles and droplets, and membrane characteristics, all of which affect absorption. 

Lipid material Extraction with pet. ether, partition with acetonitrile, addition of satd. aq NaCI to back-extract pesticides to pet. ether, additional processing GC/ECD or GC/MS No data No data Walters 1986... 

Gel permeation chromatography (GPC) with SX3 Biobeads (200-400 mesh) in a range of column sizes and solvents is used by most workers [ 189,366,400,402, 453,454,487-489]. Separation has been made primarily between lipid material > 500 A which is the first to elute from such columns followed by the smaller molecules which include most of the organic pollutants that accumulate in sample matrices. 

Many cell walls have layers in the outer regions of the wall that carry lipid material. These are cutin, suberin, and waxes (67). How these are transported to the outside of the cell wall is not known. Pores have not been found, nor has a volatile lipid solvent been detected that would carry the lipid through the hydrophilic wall. 

Solidification of the particles may not be the final step in the formation process of solid lipid particles. Lipidic materials exhibit rich polymorphism [69,70], which may also occur in the dispersed state. In nanoparticles, the polymorphic behavior of the matrix lipids may, however, differ distinctly from that in the bulk material. Polymorphic transitions are usually accelerated in the nanoparticles compared with the bulk lipids [2,62]. In some cases, polymorphic forms not observable in the corresponding bulk materials were detected in lipid nanoparticles [1,65]. Because polymorphism can affect pharmaceutically relevant properties of the particles, such as the drug incorporation capacity [65], corresponding investigations should also be included in the characterization process. As long as polymorphic or other crystalaging phenomena have not terminated, the particle matrix cannot be regarded as static, and alterations of the particle properties may still occur. 

A number of lipid materials were shown to be toxic to the larvae of the bruchid beetle, Callosobruchus maculatus (96). 

Cuticle. The cuticle of adult nematodes is relatively impermeable and is composed primarily of a complex of several proteins. These proteins include collagens, fibroids, elastoids, and keratoids, possibly hardened by tanning with pol3rphenols or quinones. Sometimes lipide materials are also present (8, 10y 52). When such lipide materials are present on the adult cuticle, they probably take the form of hydroxy fatty acids or esters of fatty acids with monohydroxy alcohols. Such materials may form ring compounds. Regardless of the exact chemical nature, the lipides are unquestionably one of the chief barriers to permeability. These materials are commonly difficult to demon-... 

Solvent extraction is an excellent choice for aroma-compound isolation from foods when applicable. Unfortunately, many foods contain some lipid material, which limits the use of this technique since the lipid components would be extracted along with the aroma compounds. Alcohol-containing foods also present a problem in that the choice solvents (e.g. dichloromethane and diethyl ether) would both extract alcohol from the product, so one obtains a dilute solution of recovered volatiles in ethanol. Ethanol is problematic since it has a high boiling point (relative to the isolated aroma compounds), and in concentration for analysis, a significant proportion of aroma compounds would be lost with the ethanol. As one would expect, the recovery of aroma compounds by solvent extraction is dependent upon the solvent being used, the extraction technique (batch or continuous), and the time and temperature of extraction. 

A commercially interesting low calorie fat has been produced from sucrose. Proctor Gamble has patented a mixture of penta- to octafatty acid ester derivatives of sucrose under the brand name Olestra. It was approved by the FDA in January 1996 for use as up to 100% replacement for the oil used in preparing savory snacks and biscuits. Olestra, a viscous, bland-tasting liquid insoluble in water, has an appearance and color similar to refined edible vegetable oils. It is basically inert from a toxicity point of view as it is not metabolized or absorbed. It absorbs cholesterol (low density lipoprotein) and removes certain fat-soluble vitamins (A, D, E, and K). Hence, Olestra has to be supplemented with these vitamins. No standard LD50 tests have been performed on Olestra however, several chronic and subchronic studies were performed at levels of 15% in the diet, and no evidence of toxicity was found. No threshold limit value (TLV), expressed as a maximum exposure per m3 of air, has been established, but it is estimated to be similar to that of an inert lipid material at 5 mg/m3. 

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