Lecithin characterization

TRXF was used to determine the trace elements in samples of lecithin, insulin, procaine, and tryptophan in an attempt to develop elemental fingerprints that could be used to determine the origin of the sample [80]. It was reported that through the use of matrix-independent sample preparation and an internal standard, one could use TXRF to facilitate characterization of the samples without the need for extensive pretreatment. In another work, a study was made of the capability of TXRF for the determination of trace elements in pharmaceutical substances with and without preconcentration [81]. 

MA Schwarz, K Raith, HH Ruettinger, G Dongowski, RHH Neubert. Investigations of interactions between drugs and mixed bile salt/lecithin micelles—a characterization by micellar affinity capillary electrophoresis. Part III. J Chro-matogr A 781 377-389, 1997. 

Ogawa, S., Decker, E.A., McClements, D.J. (2004). Production and characterization of O/W emulsions containing droplets stabilized by lecithin-chitosan-pectin multilayered membranes. Journal of Agricultural and Food Chemistry, 52, 3595-3600. 

Let us consider first lipid-lipid interaction. Urry et al, showed the existence of a positive CD band at 218 m/x and a negative CD band at about 192 m/z in phosphatidyl choline and phosphatidyl ethanolamine dissolved in trifluoroethanol (86). The 192-m/z band was not characterized in detail, but the 218-m/z band is of such position and shape that the addition of lipid and protein CD bands could produce a composite CD band, and hence an ORD Cotton effect, which is red shifted. As noted by Urry, the 218-m/z CD extremum of lecithin must arise from n — 7T transitions in the fatty acid ester groups. Although the optical activities of solutions of deproteinized membrane phospholipids determined at the same concentration as in the intact membrane are negligibly small, in membranes an ordered array of lipids could greatly enhance rotation. Such an effect could yield information on the nature of lipid-lipid association. This can be tested experimentally. Halobacterium cutirubrum offers a unique system since Kates has shown that the lipids in this extreme halophile contain ether bonds rather than ester bonds (43, 44), Hence, the n — tt transition essential to the CD band at 218 m/z in phospholipids does not exist. Nevertheless, we found that the ORD... 

Out of a variety of polymerizable lipids tested for possible use of bilayer formation, only three systems exhibited BLM lifetimes of more than a few minutes (Table 2 26)). These BLMs were characterized by measuring their resistance and capacitance (Table 2., see26> for details). The data obtained were comparable with values obtained with egg lecithin the most frequently used material for preparing BLMs. 

Although phospholipids are natural components of nearly all food products, the analysis of the phospholipid composition is of importance mainly in the certification and quality control of lecithins. According to the European Analytical Subgroup of the International Lecithin and Phospholipid Society (ILPS), there is an urgent need for a standard method for the determination of the PL composition, for this would allow a better characterization of lecithin and PL products (15,16). Besides, the nonavailability of good calibration standards is a major problem when comparing analytical results between companies. In order to try to solve the latter problem, the ILPS proposes a calibration standard whose composition is certified by 31P-NMR as an absolute tech-... 

B Hersloef, U Olsson, P Tingvall. Characterization of lecithins and phospholipids by HPLC with light scattering detection. In I Hanin, G Pepeu, eds. Phospholipids. New York Plenum Press, 1990, pp 295-298. 

Note, however that the concepts about the lipid membrane as the isotropic, structureless medium are oversimplified. It is well known [19, 190] that the rates and character of the molecular motion in the lateral direction and across the membrane are quite different. This is true for both the molecules inserted in the lipid bilayer and the lipid molecules themselves. Thus, for example, while it still seems possible to characterize the lateral movement of the egg lecithin molecule by the diffusion coefficient D its movement across the membrane seems to be better described by the so-called flip-flop mechanism when two lipid molecules from the inner and outer membrane monolayers of the vesicle synchronously change locations with each other [19]. The value of D, = 1.8 x 10 8 cm2 s 1 [191] corresponds to the time of the lateral diffusion jump of lecithin molecule, Le. about 10 7s. The characteristic time of flip-flop under the same conditions is much longer (about 6.5 hours) [19]. The molecules without long hydrocarbon chains migrate much more rapidly. For example for pyrene D, = 1.4x 10 7 cm2 s1 [192]. 

A25. Aron, L, Jones, S., and Fielding, C. J., Human plasma lecithin cholesterol acyltransferase Characterization of cofactor-dependent phospholipase activity. J. Biol. Chem. 253, 7220-7226 (1978). 

M37. Mitchell, C. D., King, W. C., Applegate, K. R., Forte, T., Clomset, J. A., Norum, K. R., and Cjone, E., Characterization ofapolipoprotein E-rich high density lipoproteins in familial lecithin cholesterol acyltransferase deficiency. /. Lipid Res. 21, 625-634 (1980). 

Soutar, A. K., Night, B. L., and Myant, N. B., The characterization oflipoproteins in the high density fraction obtained from patients with familial lecithin cholesterol acyltransferase deficiency and their interaction with cultured human fibroblasts. /. lipid Res. 23, 380-390 (1982). 

The hydrophilicity of nonionic surfactants can be characterized numerically as their hydrophile-lipophile balance (HLB). An HLB value of 3-6 indicates that the compound is a likely W/O emulsifier 7-9, a wetting agent 8-13, an O/W emulsifier 13-15, a detergent and 15-18, a solubilizer (of oil or other nonpolar compounds) in water. The HLB values of some common compounds are presented in Table 34.12.170 An HLB value of 8.0 is shown in Table 34.12 for lecithin, but manufacturers are able to supply modified lecithins with values of2-12. 

With the exception of lecithin, all emulsifiers used in foods are synthetic. They are characterized as ionic or nonionic and by their hydrophile/lipophile balance (HLB). All of the synthetic emulsifiers are derivatives of fatty acids. 

Various lecithin-based MEs were also characterized by Hasse and Keipert [131]. The formulations were tested in terms of their physicochemical parameters (pH, refractive index, osmolality, viscosity, and surface tension) and physiological compatibility (HET-CAM and Draize test). In addition, in vitro and in vivo evaluations were performed. The tested MEs showed favorable physicochemical parameters and no ocular irritation as well as a prolonged pilocarpine release in vitro and in vivo. 

Aboofazeli, R., Lawrence, C. B., Wicks, S. R., and Lawrence, M. J. (1994), Investigations into the formation and characterization of phospholipid microemulsions. Part 3. Pseudo-ternary phase diagrams of systems containing water-lecithin-isopropyl myristate and either an alkanoic acid, amine, alkanediol, polyethylene glycol alkyl ether or alcohol as cosurfactant, Int. J. Pharm., Ill, 63-72. 

Moreno, M. A., Ballesteros, M. P., and Frutos, P (2003), Lecithin-based oil-in-water microemulsions for parenteral use pseudotemary phase diagrams, characterization and toxicity studies,/. Pharm. Sci., 92(7), 1428-1437. 

In practice, commercial lecithin products are not marketed by phospholipid content, but rather by a set of unique chemical and physical properties. These properties, as indicated by product specihcations, must be understood because they are used to characterize specihc lecithin types. 

Betaine derives its name from the fact that it occurs in the molasses obtained from beets, being therefore present in the beet root. It is somewhat widely distributed in plants but not so widely as choline. Betaine is non-toxic and there is even possibility that it may be used as a food material by animals. Like lecithin it is not an individual, but represents rather a group of compounds characterized by the distinctive group... 

These experiments are characterized by that extreme selectivity usually associated only with biological processes. This led Hughes to trace a parallelism with hemolysis caused by the venoms. He found that blacksnake venom reacted with the lecithin film at a rate which was indeed related to the speed of hemolysis of washed guinea-pig cells. Further experiments, however, showed that the ability of a venom to react with a lecithin monolayer did not necessarily imply hemolytic activity towards the red cells of any given species. Black tiger venom, for example, was only very slightly reactive towards red cells, even after sixteen hours, while the venoms of copperhead and cobra as well as of blacksnake were strongly hemolytic within two hours in concentrations as low as 0.2 mg. ml. . ... 

Glycerophospholipids (PL) are abundant lipid components found in Nature [1]. Most vegetable oils, fish oil and egg yolk are particularly rich in mixtures of phospholipids. They are characterized by the presence of a polar head and two fatty acid chains in the apolar part of the molecule. The two acyl chains mainly consist of saturated fatty acid residues in the snl position and mainly (poly)unsaturated fatty acid chains in the sn2 position. Mixtures of phospholipids at low cost are obtained from the degumming process of vegetable oils. Lecithin, the main component of the mixture, has the polar head characterized by the choline residue. It is usually defined as phosphatidyl choline (PC) and it is understood that the composition of the apolar part is composed of mixtures of fatty acid residues dependent to a large extent on the source of the raw material (fatty acid chains composition of PC from soy beans palmitic 11.6%, stearic 3.4%, oleic 4.6%, linoleic 66.4%, linolenic 8.7%). Scheme 1 shows a PC with two defined acyl chains at the glycerol backbone l-palmitoyl-2-linoleoyl-5n-glycero-3-phosphocholine (PLPC). 

A number of studies have used both H and NMR spectroscopy of bile to aid characterization of its composition and structme. Thus, spectra of bile from fish exposed to petroleum have been studied. NMR spectra of human bile have also been investigated. NMR spectroscopy of bile has been used to investigate the micellar cholesterol content - and lipids " and both H and NMR have been used to study the distribution of lecithin and cholesterol. " ... 

Backlund, S., Rantala, M., and Molander, O., Characterization of lecithin-based microemulsions used as a media for a cholesterol oxidase-catalyzed reaction. Coll. Polym. Sci., Ill, 1098-1103, 1994. 

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