Lecithin analysis

L. Campanella, F. Pacifici, M.P. Sammartino and M. Tomassetti, A new organic phase bienzymatic electrode for lecithin analysis in food products, Bioelectrochem. Bioenerg., 47(1) (1998) 25-38. 

Diehl, B. W. K. and Stein, J. (1994) Calibration standards for lecithin analysis using HPLC with light scattering detector. 84th AOCS Annual Meeting and Exposition, Atlanta, GA, May 1994 copy available from author. 

The standard methods (26) of analysis for commercial lecithin, as embodied in the Official and Tentative Methods of the American Oil Chemists Society (AOCS), generally are used in the technical evaluation of lecithin (27). Eor example, the AOCS Ja 4-46 method determines the acetone-insoluble matter under the conditions of the test, free from sand, meal, and other petroleum ether-insoluble material. The phosphoHpids are included in the acetone-insoluble fraction. The substances insoluble in hexane are determined by method AOCS Ja 3-87. 

The total phosphoms content of the sample is determined by method AOCS Ja 5-55. Analysis of phosphoUpid in lecithin concentrates (AOCS Ja 7-86) is performed by fractionation with two-dimensional thin-layer chromatography (tic) followed by acid digestion and reaction with molybdate to measure total phosphorous for each fraction at 310 nm. It is a semiquantitative method for PC, PE, PI, PA, LPC, and LPE. Method AOCS Ja 7b-91 is for the direct deterrnination of single phosphoHpids PE, PA, PI, PC in lecithin by high performance Hquid chromatography (hplc). The method is appHcable to oil-containing lecithins, deoiled lecithins, lecithin fractions, but not appHcable to lyso-PC and lyso-PE. 

Kansy et al. [550] reported the permeability-lipophilicity relationship for about 120 molecules based on the 10% wt/vol egg lecithin plus 0.5% wt/vol cholesterol in dodecane membrane lipid (model 15.0 in Table 7.3), shown in Fig. 7.23. The vertical axis is proportional to apparent permeability [see Eq. (7.9)]. For log Kd > 1.5, Pa decreases with increasing log Kd. In terms of characteristic permeability-lipophilicity plots of Fig. 7.19, the Kansy result in Fig. 7.23 resembles the bilinear case in Fig. (7.19d). Some of the Pa values may be underestimated for the most lipophilic molecules because membrane retention was not considered in the analysis. 

Figures 7.31a-c clearly show that after some critical soy content in dodecane, Pe values decrease with increasing soy, for both sink and sinkless conditions. [This is not due to a neglect of membrane retention, as partly may be the case in Fig. 7.23 permeabilities here have been calculated with Eq. (7.21).] Section 7.6 discusses the Kubinyi bilinear model (Fig. 7.19d) in terms of a three-compartment system water, oil of moderate lipophilicity, and oil of high lipophilicity. Since lipo-some(phospholipid)-water partition coefficients (Chapter 5) are generally higher than alkane-water partition coefficients (Chapter 4) for drug-like molecules, soy lecithin may be assumed to be more lipophilic than dodecane. It appears that the increase in soy concentration in dodecane can be treated by the Kubinyi analysis. In the original analysis [23], two different lipid phases are selected at a fixed ratio (e.g., Fig. 7.20), and different molecules are picked over a range of lipophilicities.

Miyoshi, H. Maeda, H. Tokutake, N. Fujita, T., Quantitative analysis of partition behavior of substituted phenols from aqueous phase into liposomes made of lecithin and various lipids, Bull. Chem. Soc. Jpn. 60, 4357-4362 (1987). 

The few examples of deliberate investigation of dynamic processes as reflected by compression/expansion hysteresis have involved monolayers of fatty acids (Munden and Swarbrick, 1973 Munden et al., 1969), lecithins (Bienkowski and Skolnick, 1974 Cook and Webb, 1966), polymer films (Townsend and Buck, 1988) and monolayers of fatty acids and their sodium sulfate salts on aqueous subphases of alkanolamines (Rosano et al., 1971). A few of these studies determined the amount of hysteresis as a function of the rate of compression and expansion. However, no quantitative analysis of the results was attempted. Historically, dynamic surface tension has been used to study the dynamic response of lung phosphatidylcholine surfactant monolayers to a sinusoidal compression/expansion rate in order to mimic the mechanical contraction and expansion of the lungs. 

Determination of Wax + Lecithin. The percentages of TNT, RDX plus Nitrocellulose, Ca chloride, and aluminum are added and their sum subtracted from 100 percent. The remainder is taken to be the percentage of wax plus lecithin 4.4.3.4 Method of Analysis. Grade B... 

Where the method of analysis described in 4.4.3.3 is not used in its entirety, the wax plus lecithin content can be detd as follows The crucible plus residue obtd after the RDX satd benzene extraction as described in 4.4.3.3.1 is extracted with an additional 50ml of RDX satd benzene (5—10ml portions, 30 secs each). The sample is dried at 100°C for 30 mins. The crucible... 

HBX-1 Analytical Procedure. Pristera (Ref) briefly describes its analysis as follows Extract TNT wax and lecithin with carbon tetrachloride then determine TNT by titanous reduction as described on p 466 of Ref extract with water the Ca chloride from carbon tetrachloride insoluble residue and extract RDX, with hot toluene, from water-insol residue using Wiley extractor. Extract NC from toluene-insol residue with cyclohexanone, acetone, or tetrahydrofuran the remainder is A1... 

For mixtures of lecithin plus Na cholate it appears possible to infer the molecular arrangement in the dispersed micelles from the most likely structure of the liquid crystalline phase suggested by x-ray analysis. However, there are cases where dispersion is not possible because neither component is sufficiently hydrophilic to be dispersed even when alone in water. This is shown by the association of cholesterol and lecithin in the presence of water. The ternary diagram of Figure 4 is relative to these systems. Here only the lamellar liquid crystalline phase is obtained (region 1< in Figure 4). This phase is already given by lecithin alone, which can absorb up to 55% water. Cholesterol can be incorporated within this lamellar phase up to the proportion of one molecule of choles-... 

Materials. The water used for all purposes was double-distilled (once with glassware) and deionized (final conductance was less than 1 X 10"6 ohm1 cm."1). Stearic acid (obtained from Sigma Chemical Co.) was at least 99% pure as determined by silica gel thin-layer chromatography (4), and the synthetic L-a(/ ,y-dipalmitoyl) lecithin was about 90% pure (see Ref. 13 for analysis). The ATP-14C and its derivatives were obtained from Nuclear-Chicago or New England Nuclear Corp. and were found to be 95-98% pure as determined by cellulose thin-layer chromatography (16). 

The phosphoric acid esters of diacyl glycerides, phospholipids, are important constituents of cellular membranes. Lecithins (phosphatidyl cholines) from egg white or soybeans are often added to foods as emulsifying agents or to modify flow characteristics and viscosity. Phospholipids have very low vapor pressures and decompose at elevated temperatures. The strategy for analysis involves preliminary isolation of the class, for example by TLC, followed by enzymatic hydrolysis, derivatization of the hydrolysis products, and then GC of the volatile derivatives. A number of phospholipases are known which are highly specific for particular positions on phospholipids. Phospholipase A2, usually isolated from snake venom, selectively hydrolyzes the 2-acyl ester linkage. The positions of attack for phospholipases A, C, and D are summarized on Figure 9.7 (24). Appropriate use of phospholipases followed by GC can thus be used to determine the composition of phospholipids. 

Margarine -m tall oil [CARBOXYLIC ACIDS - FATTY ACIDS FROM TALL OIL] (Vol 5) -food additives m [FOOD ADDITIVES] (Vol 11) -food packaging for [FOOD PACKAGING] (Vol 11) -lecithin m [LECITHIN] (Vol 15) -nut oils m [NUTS] (Vol 17) -trace analysis of [TRACE AND RESIDUE ANALYSIS] (Vol 24) -useofsorbates [SORBIC ACID] (Vol 22)... 

Up to now, however, HPLC has remained the method of choice. This is due mainly to the fact that this technique is much easier to automate as compared to TLC. Besides, a wide variety of stationary and mobile phases are available, so the technique is highly flexible. Besides, the investment cost is much lower as compared to P-NMR, whereas quantitation is more straightforward than in MEKC. Hence, the more recent official methods for the analysis of phospholipids, as proposed by the American Oil Chemists Society (AOCS), by the International Union for Pure and Applied Chemistry (IUPAC), and by the International Lecithin and Phospholipid Society (ILPS), all use HPLC. In this chapter, a review is presented of HPLC procedures that have been described during the past 10 years the older literature was discussed in a previous edition of this handbook (21). 

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-... 

J De Kock. The European Analytical Subgroup of ILPS—a joint effort to clarify lecithin and phospholipid analysis. Fat Sci Technol 95 352-355,1993. 

R Szucs, K Verleysen, GS Duchateau, P Sandra, BGM Vandeginste. Analysis of phospholipids in lecithins. Comparison between MEKC and HPLC. J Chromatogr A 738 25-29,1996. 

K Verleysen, P Sandra. Analysis of phospholipids in lecithins separation according to hydrophobic-ity by lowering the temperature. J High Resol Chromatogr 20 337-339, 1997. 

SL Melton. Analysis of soybean lecithins and beef phospholipids by HPLC with an evaporative light scattering detector. J Am Oil Chem Soc 69 784-788, 1992. 

WL Erdahl, A Stolyhwo, OS Privett. Analysis of soybean lecithin by thin layer and analytical liquid chromatography. J Am Oil Chem Soc 50 513-515, 1973. 

A statistical thermodynamic analysis indicates that a pure lecithin molecule in water will aggregate to bilayers with a maximum disorder due to uncompensated charges58. They represent unstable fabrics, where the thickness of the bilayers varies with the amount of incorporated water. 

S. Pati, M. Quinto, F. Palmisano and P.G. Zambonin, Determination of choline in milk, milk powder, and soy lecithin hydrolysates by flow injection analysis and amperometric detection with a choline oxidase based biosensor, J. Agric. Food Chem., 52(15) (2004) 4638-4642. 

Vergey, A. L., Kody, M. H., and Gershfield, N. L. (1981). Quantitative analysis of disaturated lecithins in human plasma by ammonia chemical ionisation mass spectrometry. Biomed. Mass Spectrom. 8, 503-505. 

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