LECITHIN

Yu. A. ShchipunovRussian Academy of Sciences, Vladivostok, Russia

Lecithin is a most prominent member among the surfac-

tants. It has a long history of use, dating back in antiquity.

The ancient Greeks e.g., treated leather with dried egg

yolk, which contains up to 30 wt% lecithin, to remove fats

and oils, making it softer. At present time it is used in

every day life and in many fields, including foods, animal

feeds, pharmaceuticals, cosmetics, and a variety of indus-

trial applications. Lecithin is also one of the most popular

substances studied by academic scientists. The strong in-

terest in it and widespread use can be explained at least by

three main reasons; 1) lecithin can be found in any living

matter because it is one of the main constituents of the

lipid matrix of the biological membranes, 2) it is a bio-

compatible naturally occurring surfactant, and 3) it pos-

sesses varies functionalities. Lecithin in solutions forms

micelles and liposomes, self-organizes into liquid-crystal-

line structures, disperses and stabilizes dispersions, and

provides wetting and coats surfaces, inducing their mod-

ification. Its properties and properties of self-organized

structures have been and are still under intensive inves-

tigations. There are thousands of publications concerning

lecithin. The framework of a short review does not allow

discussing all its properties and structures in sufficient

details. Therefore, the article should be taken as an intro-

duction to the colloid chemistry of lecithin. The discussion

of the main subject is preceded by a consideration of no-

menclature, structure, sources, composition, and process-

ing, and it is accomplished by a description of numerous

field of lecithin application.

NOMENCLATURE, STRUCTURE, SOURCES,COMPOSITION, AND PROCESSING

Lecithin is a trivial name for 1,2-diacyl-sn-glycero-3-

phosphocholine (1). It was usually applied to a crude

mixture of phospolipids and tracylglycerols obtained as a

by-product upon refining of seed oils. Although the

IUPAC-IUB Commission did not recommend, the trivial

name is widely used in the academic literature to designate

a purified substance from natural sources. But initially, the

term was suggested by Maurice Gobley. He derived it from

the Greek word lekithos for egg yolk, from which the le-

cithin in the form of a sticky, orange-colored material was

isolated as early as 1850 (2).

Lecithin belongs to the phosphoglycerides (1, 3–6).

This class of substance are based on diacyl derivatives of

3-glycerophosphoric acid (see Fig. 1) A choline is joined

in an ester linkage to the second hydroxyl group of the

phosphoric acid residue that gives 1,2-diacyl-sn-glycero-

3-phosphocholine, called often phosphatidylcholine (PC).

The last-mentioned term includes ‘‘phosphatidyl’’ in place

of ‘‘1,2-diacyl-sn-glycero-3-phospho.’’ Phosphoglycer-

ides are also named in the literature as glycerophospho-

lipids. This name stresses that they are among phospho-

lipids (PLs), i.e., among the class of substances that have a

phosphate group, and relate to lipids—a wide range of

compounds containing, as suggested by Gunstone (5),

‘‘fatty acid residues or closely related compounds such as

the corresponding alcohols and the sphingosine bases.’’

It would be well to mention other major PLs. They

differ from lecithin, as obvious from Fig. 1, by the end

functional group replacing the choline. Sometimes one

fatty acid residue in a lecithin molecule is absent, that

gives a monoacyl form, known as lysolecithin. Noteworthy

also are phosphocholine-containing PLs, of which the ba-

sic backbone of the molecule is presented by a long-chain

aminodiol, sphingosine (Fig. 1), instead of glycerol. They

are usually called sphingomyelin. The sphingolipids are

among the major naturally occurring PLs, being some-

times as alternative to lecithin in animal (mainly nervous)

tissues (6, 7).

The structural formula of lecithin in Fig. 2 is a steric

representation in the Fisher projection of the glycerol de-

rivatives. As suggested by the IUPAC-IUB Commission

(8), the top carbon atom of a vertically oriented glycerol

chain is designated as C-1 and the rest atoms as C-2 and

C-3. The prefix sn (stereospecifically numbered) imme-

diately ahead of the term ‘‘glycerol’’ in the name of the

substance is indicative of such numbering. Although two

fatty acid residues in a lecithin molecule appear as an

interchangeable, they are not, however, equivalent from

L

Encyclopedia of Surface and Colloid Science 2997Copyright D 2002 by Marcel Dekker, Inc. All rights reserved.

the stereochemical point of view (6). This difference re-

veals itself in natural lecithins, which bear usually satu-

rated acids at the sn-1 position and unsaturated ones at sn-

2 position (6, 9). Moreover, there are phospholipases A1

and A2 in the living cell that cause a selective cleavage

of either the C-1 ester or the C-2 ester linkages, respec-

tively (10, 11), thus demonstrating the stereochemical

asymmetry of the native PLs.

The phosphocholine residue contains oppositely

charged groups, while the lecithin possesses a zwitterionic

character. A pK for a choline residue is near 13,9, while

for the phosphate group it is below 2 (6, 12, 13). Therefore,

the lecithin molecule has a net neutral charge over about

the entire pH range.

The PLs form the lipid matrix of biological membranes

and membranous organelles (14). Their total amount va-

ries from 5 to 60%, among which lecithin frequently

accounts for 50–60% (7, 15–18). In view of the fact

that the biological membranes are the basic structural

element of the cell, the lecithin can be found almost in

any living matter.

Commercial lecithin is a complex mixture of PLs

shown in Fig. 1 as well triglycerides, fatty acids, and

carbohydrates (7, 16–19). The exact composition depends

on the source of the lecithin as well as on the method of

extraction and purification (18, 20–23). Table 1 provides

representative data on the lecithin distribution in some

species that demonstrates a variability of PL content even

from organ to organ. In addition, there are notable dif-

ferences in the fatty acid residues. Illustrative examples

for fatty acid composition of lecithins separated from

industrially important sources are given in Table 2. Al-

though lecithin can be found, as mentioned previously, in

all kinds of living matter, it is predominantly manufac-

tured from plant seeds, mainly from soybean oilseeds and

to a lesser degree from cottonseeds, peanut, sunflower,

and rape seeds (7, 17, 23). From animal sources, egg yolk

Fig. 1 General structural formulas for phospholipids.

Fig. 2 General formula for lecithin presented in a Fischer

projection.

2998 Lecithin

and brain tissues (bovine brain) are primarily used (16,

23, 24).

Lecithin from plant sources is commonly obtained as a

by-product at a pretreatment stage of the oil refinement.

The technological process is based on the hydration of

PLs after an addition of water into oil and their subse-

quent precipitation in the gumlike form . That is why the

stage is known as degumming (20, 22, 23). The water

amount needed to remove PLs is approximately equal to

their content in the oil (2–3 wt% in soybean oil). The

degumming is performed at 60–75�C during 0.5–1.0 h if

it is a batch process (20–23). On separating the precipi-

tated gum by means of the centrifuge, one will have a

fatty-like mass, from light brown to yellow or reddish

brown in color. This is a mixture of PLs containing in

accordance with a various published data 12–46% leci-

thin, 8–34% PE, 1.7–21% PI, 0.2–14% PA, 0.2–6.3%

PS, and 1.5–8.5% lysolecithin (see Fig. 1) (5, 9, 17–20,

22). Then pure PLs can be obtained by fractionation and/

or separation of the initial crude lecithin (6, 20, 22, 23). It

can be also modified by means of chemical or enzymatic

treatment to have a mixture with desired properties (18,

19, 23, 33–37).

Lecithin from animal sources—mainly from egg yolk

and to a lesser degree from brain tissues—is not manu-

factured as the by-product. The technological processes

differ from previously described ones owing to tight bind-

ing of PLs with proteins. To separate them, the extraction

by means of such polar solvents as alcohols (ethanol or

iso-propanol) and ethyl acetate is often applied (16, 22–

24). A mixture of PLs thus obtained from egg yolk is

enriched with lecithin in distinction to vegetable products.

It can be contain, as reported by various authors (16), 66–

87% lecithin as well as 8–24% PE, trace to 3% PS, 1–6%

SM, and 2.5–6% lyso-PLs (18, 22–24). The egg lecithin

has a higher price than the soybean one, and hence is

mainly used in pharmaceuticals.

The living systems possess remarkably constant lipid

composition that is rather resistant to a change in envi-

ronmental conditions and diet. Results with the improve-

ment of dietary quality of the yolk egg of the domestic

hen for human consumption can provide an illustrative

example. There was an idea to produce ‘‘polyunsaturated

low-cholesterol eggs’’ by dietary and genetic means. Nu-

merous attempts showed that the initial optimism was

premature. The diet led to some changes in the lipid com-

position and cholesterol content, but it proceeded in a

compensatory manner (24). For instance, the reduction of

cholesterol was accompanied, as shown by Kudchodhar et

Table 2 Fatty acid composition of lecithins from commercial sources

Lecithin

Residuea

16:0 18:0 18:1 18:2 18:3 20:4 22:6 24:4

Egg yolkb 67/0 26/0 5/51 0/24 — 0/7 0/4 0/4

Bovine brainc 55/25 22/0 8/49 — — 0/11 — —

Bovine liverd 18/8 33/0 2/21 — — 0/10 — —

Soybean oile 34/1 8/2 8/5 43/5 5/7 — — —

aValues are expressed as mol%. The first number in columns shows the amount of fatty acid residue in sn-1 position, the second in sn-2 position; the acids

with an amount is < 2 mol% are not shown or are taken equal to zero.b(From Ref. 24.)c(From Ref. 32.)d(From Ref. 16.)e(From Ref. 9.)

Table 1 Lecithin distribution in various organs of different

species

Organ

Skeletal

Species Heart Liver Lung Kidney muscle Brain

Human 40.0c 43.6c 50.4a 33.1g 53.9a 29.2a

Bovine 40.7a 54.0a 39.5e 33.8a 42.5c 29.6a

Sheep 25.5c 39.7c 58d 35.8c — 37.3c

Mouse 40.6e 45.6c 49.4a 35.6g 55.9a —

Rat 36.0e 54.6f 57.5h 34.3g 51.1e 36.8e

Frog 39.6e 46.5g 46.5a 34.3g 55.2e 45.0b

Lobster — — — — 55.7a 58.4a

Values are percentage of total PLs.a(From Ref. 25.)b(From Ref. 26.)c(From Ref. 27.)d(From Ref. 28.)e(From Ref. 16.)f(From Ref. 29.)g(From Ref. 30.)h(From Ref. 31.)

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Lecithin 2999

al. (38) and Clarenburg et al. (39), by an absorption of ste-

rols from feeding plants that gave only marginal success.

A genetic selection has not also allowed realizing the de-

sired improvement of the lipid and cholesterol compo-

sition for the egg yolk of the domestic hen. This is ex-

plained why the PLs produced from the same natural

sources collected from place to place on the Earth de-

monstrates a low variability in their chemical composition

and physico-chemical properties. This uniformity has the

great importance for the industrial applications and scien-

tific research.

PHYSICO-CHEMICAL AND COLLOIDPROPERTIES IN SOLUTIONS

Lecithin is soluble or dispersal practically in all solvents

including aliphatic, halogenated, and aromatic hydrocar-

bons, alcohols, esters, and ethers, water, and aqueous so-

lutions (3, 12, 23, 40). The one exception is presented by

acetone and a number of ketones. Acetone is widely app-

lied to precipitate lecithin from solutions and/or separate it

from acetone-soluble substances (e.g., triglycerides), pro-

viding a convenient method for its purification (20–23).

Lecithin is prone to self-organize into various colloid

structures in its solutions. This depends strongly on the

type and nature of solvent. Furthermore, the presence of

impurities or other PLs, as in commercial samples, causes

significant change of phase behavior and properties of

formed structures. It is often used in practice. More than

40 various formulations are suggested by manufactures

for different applications (19–23). This article is mainly

devoted to pure lecithin. The common approaches used to

develop formulations will be considered at the end.

Binary Systems

Lecithin-water

Lecithin is insoluble in water. It can be only dispersed (3,

12–42, 40–42). Lecithin forms true solutions at very

small concentrations because of its strong liability for

self-assembling into aggregates. For example, the critical

micelle concentration (cmc) for dipalmitoylphosphatidyl-

choline is equal to 4.6 � 10�10 mol/dm3 (43). A shorten-

ing of each of both the fatty acid residues by one meth-

ylene group results in increase of the cmc in about one

order of magnitude. For instance, the cmc values for leci-

thin containing C8-,C7-, and C6- hydrocarbon chains are

equal to 0.2–0.3, 2, and 15 mM, respectively (44). A

detailed study performed by Marsh and King (45) showed

that the cmc does not change so sharp with the hydro-

carbon chain length. They suggested the following ex-

pression ln[cmc] = � 0.4–1.7nC for a dependence of the

critical micellar concentration on the number of carbon

atoms nC in the fatty acid residues.

Micellar aggregates, however, are not common for

naturally lecithin in the aqueous solutions. It usually self-

organizes into liquid-crystalline structures (3, 12, 40–42).

The binary phase diagram combined for soybean and egg

yolk lecithins is presented in Fig. 3. One can see that the

lameller liquid-crystalline mesophase La is predominant

for both the lecithins. The La mesophase consists of

bimolecular layers in which the molecules are oriented

with their hydrocarbon radicals toward the inside, while the

polar groups cover both the opposite surfaces (3, 41, 46–

48). Its schematic drawing is also given in Fig. 3. Water

molecules surround the functional groups as a hydration

shell and fill interlayers, thus separating the lamellae. The

bimolecular layer has a thickness varying between 4 and 6

nm. A lecithin molecule can occupy an area from 0.6 up to

1.0 nm2 (3, 41, 46, 48). The parameters of a bimolecular

layer depend on the fatty acid residues in the PL molecule

and water amount introduced. When being successfully

added to lecithin, water is absorbed by lamellae that causes

a change of their parameters; the thickness is decreased,

while the area occupied by 1 a lecithin molecule is in-

Fig. 3 Binary phase diagrams for egg yolk and soybean leci-

thins. The latter is shown by dashed lines. As obvious, the main

naturally occuring lecithins are not much different from each

other in the phase behavior. Insets present schematic represen-

tations of the liquid crytalline states. Their notations are made in

accordance with Luzzati suggestion. (From Ref. 40.)

3000 Lecithin

creased (3, 40). This has an important consequence. Be-

cause of the opposite change in the thickness and molecular

area with the water addition, the lecithin molecules holds

its cylindrical shape that makes the La mesophase stable

over a wide range of concentrations (49).

The La mesophase is of fundamental importance for

lecithin. The bimolecular layer is the basic structure of

vesicles (liposomes) (15, 41, 48, 50). As obvious from the

phase diagram (Fig. 3), lecithin forms a homogeneous

lamellar phase at a water concentration ranging from 7 to

10 wt% up to ca. 45 wt%. At a higher concentration, there

is a two-phase system in which the La mesophase coexists

with an aqueous solution. This is a region for vesicle

(liposome) formation. If a dried lecithin is placed in an

excess of water, it swells, forming characteristics cylin-

drical structures called myelin figures (3, 40, 51). The

process is illustrated by a set of pictures in Fig. 4. The

myelin figures were first described by Virchow in 1854

(51). Their formation is caused by expulsion of bimole-

cular lamellae from the bulk owing to the swelling. This

explains why the myelin figures are composed of coa-

xially arranged bimolecular layers (52–54). The process

is terminated by disintegration of the myelin figures into

spherical and oval particles. They stand for multilamellar

vesicles of which the structure can be represented as a

spherical particle with an inner aqueous core surrounded

by a shell made up of numerous closed bimolecular la-

yers. Oligolamellar—the shell consists of layers—and

unilamellar vesicles can be prepared from the multila-

mellar ones by means of mechanical treatment, e.g., so-

nication (41, 45). Their size varies between 0.01 and 100

mm, which depends mainly on the method used for the

visicle preparation (40, 41, 55). The thickness of a la-

mellae each involved into the shell is rather constant and

equal to about 40–50 nm.

It is worth mentioning that the fast uptake of lecithin

vesicles takes place in vivo by the cells of the mono-

nuclear phagocytic and reticuloendothelial systems when

they are introduced intravenously. To avoid it, lecithin is

modified or the vesicle surface is protected by introducing

various substances (see, e.g., Refs. 56, 57; some details

are considered in Polymer-lecithin complexes section).

Other liquid crystalline mesophases are formed at con-

centrations of water in lecithin < 10 wt% (Fig. 3). They

are also mainly among the lamellar type (Lb or Pb) (47).

The nonlamellar (hexagonal HII and cubic Qa) meso-

phases exist at higher temperatures ( > 90�C). The meso-

phase La transfers into Qa and then into HII with heating.

The transition from bimolecular to nonlamellar states is

brought about by a difference in the expansion of the

polar and nonpolar regions of molecules (41, 47). The

thermal activation leads to a change in hydrocarbon chain

conformations owing to trans-cis transition along C-C-C

chains. As a result, the nonpolar part of the bimolecular

layer expands more with heating than the polar region,

which leads to a change from the cylindrical shape of mo-

lecules to a conical one.

Lecithin shows a strong affinity for water (40, 58).

Dried samples are capable of absorbing water vapor. Up

to 20 or 21 water molecules per lecithin molecule can be

attached (59). This depends on the air humidity. The ab-

sorbed solvent forms a hydration shell of the polar region.

The whole hydration shell can include from 33 to 39 wa-

ter molecules (3, 60, 61), but it is completed only after

the direct contact of lecithin with water.

The hydrating water is normally subdivided into four

types (40, 58, 60). The first one or two absorbed H2O

molecules are called ‘‘inner’’ or ‘‘strongly bound’’ water.

They are linked so strongly with lecithin that they cannot

easily removed when it is dried. The following portion

forms a basic hydration shell around the polar region of

the lecithin molecule. It can include 5 to 11 solvent mol-

ecules. This type is known as ‘‘bound’’ water because of

its reduced mobility. The next type, termed ‘‘included’’ or

‘‘trapped’’ water, comprises 4 to 11 molecule. The rest of

the H2O is located in the outer part of the hydration shell,

filling mainly an aqueous interlayer between the bimole-

cular layers. When beginning the absorption, the first 3–5

solvent molecules are bounded with a phosphate group of

a lecithin molecule (Figs. 1 and 2) by means of hydrogen

bonds (40, 60, 62, 63). The following added water mole-

cules are attached to carbonyl groups and then form a

shell around a choline group.

The hydration of lecithin proceeds through few stages

(64). The absorption of the first water molecules, which

are attached to the phosphate group of the lecithin mole-

cule, takes place in a rather short time interval, less than a

minute. With filling the hydration shell, the rate of pro-

cesses becomes progressively slower. At the end stage, it

can reach up to ca. 1 h.

Lecithin-organic solvent

Lecithin is soluble, as mentioned above, in the most or-

ganic solvents. By self-organized lecithin structures, they

can be subdivided into two main types (40). The first one

is represented by organic solvents in which lecithin can

dissolve, forming true solutions and reverse micelles at

larger concentrations. This is the largest group. The sec-

ond type comprises solvents of which molecules form

numerous hydrogen bondings in the bulk. Lecithin are

capable of self-assembling in such the media, much like

in water, into liquid crystalline structures, demonstrating

lyotrophic mesomorphism.

L

Lecithin 3001

Reverse micelles: The inner volume of aggregates is

occupied by polar groups of lecithin molecules, while the

hydrocarbon chains are directed outward. The cmcs for

lecithin in benzene and n-decane are around 10 (65) and 3

(66) mM, respectively. The aggregation numbers for some

solvent media are presented in Table 3. There is rather

Fig. 4 Different stages of soybean lecithin swelling in water (A, F) and water-glycerol (30–70 v/v %) mixture (B–E) as it is observed

under the polarizing microscope. Glycerol was added to slow down the process. Photographs A–C show various types of myelin

figures. They were taken within 7 min (A), 25 min (B), and ca. 3 h (C) after a dried lecithin sample was brought into a contact with a

solvent. The myelin figures developed in water (A) are normally thinner than those obtained in the water-glycerol mixtures (B, C). The

vertical arrow in (C) marks helical myelin figures observed at an advanced stage. (D–F) Succeding stages of swelling. The beginning of

disintegration of myelin figures is presented in (D). The texture called "oily streaks" is seen in (E). This is typical of liquid crystals

possessing a well-organized lamellar structure. The closing stage is illustrated by a picture of vesicles (F). They can be obtained only

when a sample is placed in an excess amount of water. The vesicles seen with the polarizing microscope look like spherical particles

intersected with perpendicular dark lines (a cross). The appearance of the myelin figures after the contact of a solid substance with a

liquid is evidence that it is the La mesophase. This test is simple to perform, but it shows or confirms that the substance has multilamellar

structure (see the inset in Fig. 3) at these conditions. To make the presented photograhs, a small amount of dried lecithin and one or two

drops of water or its mixture with glycerol were placed on a glass plate and then covered with another one. The microscopic

observations were performed by a Carl Zeiss polarizing microscope equipped with a camera. Magnification � 100.

3002 Lecithin

wide scatter in the data, as seen for benzene solutions, ob-

tained by various authors. The reason might be in the

noncooperative nature of lecithin aggregation, which is

the common case when the surfactants self-assemble in

nonpolar media (67). In addition, the presence of even

trace amounts of water in organic solvents could strongly

influence the micellization (12, 40, 68). These factors

usually hinder the right determination of the aggregation

parameters.

There was made an attempt by Elworthy et al. (69) to

relate the micelle formation by lecithin to the dielectric

constant of organic solvents. The idea was based on expe-

riments in which mixtures of benzene with ethanol were

used. It was found that lecithin did not form micelles at

the dielectric constant equal to 29.0. What is more, a tran-

sition from reverse to direct micellar aggregates was ob-

served in this mixture. However, this idea was not sup-

ported with other data published in the literature (40, 58).

Nonaqueous liquid crystals: Lecithin is capable of

self-organizing into a liquid-crystalline state in such orga-

nic solvents as glycerol, ethylene glycol, and formamide

(40). The main feature of them is that they are prone to a

formation of numerous hydrogen bonds (75). When the

number of the H-bondings is decreased, as with forma-

mide derivatives prepared by a successive attachment of a

methyl group to the amino group, the liquid crystals cease

forming (76); e.g., lecithin in methylformamide is still

self-assembling into the liquid-crystalline state, though in

a shorter concentration range by comparison with its for-

mamide solutions, while these structures are not found

in dimethylformamide.

The formation of hydrogen bonds by the solvents, how-

ever, is the needed, but insufficient prerequisite (40).

Ethanol is an example. Lecithin self-assembles into mi-

cellar aggregates (Table 3), but its liquid crystals have not

been found in ethanolic solutions. Ethanol molecules are

linked to each other through hydrogen bonds arranged in

linear chains, whereas glycerol, ethylene glycol, and for-

mamide form three-dimensional networks from H-bon-

dings in the bulk (75). The same structural organization is

inherent in water. This provides a basis for hydrophobic

effects in water and solvophobic effects in the mentioned

organic solvents (42, 77). Surfactant molecules have a

tendency to minimize the contact area of their hydrocar-

bon chains with the solvent molecules. The lecithin self-

assembling into the liquid-crystalline state in glycerol,

ethylene glycol, and formamide is related in (40) to the

solvophobic effects.

As for the aqueous solutions, a predominant structure

for lecithin in glycerol, ethylene glycol, and formamide is

the La mesophase. Lecithin molecules are arranged in bi-

molecular layers of which the surface is covered with the

polar groups and the inner part is occupied by the hydro-

carbon chains. The solvent molecules create a solvation

shell around the functional groups of lecithin and fill in-

terlayers between bimolecular layers (76, 78). In a case of

ethylene glycol it was shown by means of a NMR spec-

troscopy that three types of solvent molecules could be

recognized by their mobility (78, 79). The same situation,

as considered in Lecithin-water section, was observed for

the hydration of lecithin in the La mesophase by the water

molecules.

It is common for molecules of the organic solvents in

the lamellar crystals not to penetrate into the region oc-

cupied by fatty acid residues. A special case is established

for benzene solutions. Lecithin self-assembles typically

into reversed micelles in benzene (Table 3). When con-

centrated solutions were cooled, a thickening was ob-

served (80). A detailed study revealed the presence of a

structure resembling the La mesophase (80, 81). Benzene

molecules are found in the regions of both the polar

groups of lecithin molecules and the hydrocarbon chains.

It should be pointed out that the capability of lecithin

to be self-organized into the lamellar structures is fun-

Table 3 Critical micelle concentrations for egg yolk lecithin in organic solutions

Solvent Aggregation number Concentration range (mM) Temperature (�C) Refs.

n-Heptane 5 > 0.01 25 66

Benzene 4– 6 < 0.1 25 12, 68, 70

73 > 1 25 68

55 40

15 15– 192 37 71

Toluene 82 3.7–15 25 72

65 40

Chloroform � 3 10– 130 1.5–44 73

Diethyl ether � 40 7– 10 25 74

Ethanol 9 3– 13 20 69

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Lecithin 3003

damental importance for the living matter (82). The living

cycle of plants includes drying and cooling during the

winter season. This proceeds also with plant seeds, yeast

cells, fungal spores, and some microorganisms. The

drying and decreased temperature result in the transition,

as obvious from the phase diagram in Fig. 3, into a crys-

talline state. When the temperature has been increased

and water has been added, the disruption of the biological

membranes takes place. Therefore, it is a vital necessary

for the living systems to retain their intact structure after

the winter season. The retention of the La mesophase is

achieved by an exchange of water for polyols (glycerol

and ethylene glycol), disaccharides (trechalose and suc-

rose), or amino acids (proline) (83).

Ternary Systems

Ternary mixtures include normally water and oil. Lecithin

concentrates mainly at the interfacial boundaries, provid-

ing a stabilizing effect on various structures. Among them,

one can prepare swollen micelles, organogels, emulsions,

and liquid crystals. These systems are characterized below.

Swollen micelles

The micelle formation usually occurs in the organic media.

Therefore, the further consideration concerns reversed mi-

cellar aggregates.

Lecithin maintains its hygroscopy when it is dissolved

in nonaqueous solutions (40, 58). Water is absorbed from

the contacting air phase. From 15 up to 30 water mole-

cules per lecithin molecule can be attached to its polar

region as a hydration shell (70, 84, 85). It should be poin-

ted out that the initial spherical shape of micelles is not

changed in aromatic (benzene and toluene) and chlorina-

ted (chloroform and tetrachloride carbon) solvents (40, 58).

By dissolving water in the lecithin solution, one can ob-

tain swollen micelles. They consist of an inner water drop-

let (core) that is surrounded by a lecithin monolayer. Its

maximum diameters in benzene and tetrachloride carbon

solutions are 5.0 ± 1.5 and 3.0 ± 0.5 nm, respectively (84).

Organogel

The most common phenomenon for the nonaqueous le-

cithin solutions induced by dissolved water is a trans-

formation of the spherical micelles into cylindrical ag-

gregates (86, 87). Their molecular model is considered in

Nonaqueous systems section. The micellar shape change

takes place in more than 50 solvents including linear and

branched alkanes, cycloalkanes, ethers, and esters (86).

For example, in a case of n-decane or cyclohexane the

dissolution, respectively, of 2–3 or 7–10 water molecules

per lecithin molecule yields cylindrical aggregates of con-

tour length up to 1 mm, while the diameter is of about 5–7

nm (88, 89). Such the micelles entangle, making up a

temporal three-dimensional network in the bulk, much as

linear polymer molecules do it in semidilute solutions or

melts. This brings about a similar sharp increase in the

solution viscosity (90, 91). In place of the low viscous so-

lution, one will find a jelly-like phase (organogel). Owing

to similarity in the structural organization of the three-

dimensional network and the rheological behavior, these

lengthy cylindrical aggregates are known in the literature

as ‘‘polymer-like’’ micelles. They are also called ‘‘worm-

like’’ or ‘‘threadlike’’ micelles, ‘‘living’’ or ‘‘equilibrium’’

polymers.

The lecithin organogels are transparent, viscoelastic li-

quids. Their rheological behavior obeys a Maxwell model

(91, 92). This means that it can be presented in the form

of a dash-pot and spring connected in parallel. From the

structural point of view, the organogel is formed with a

three-dimensional network that is temporal, without fixed

contacts between entangled polymer-like micelles. The

dynamic behavior is described in the framework of a rep-

tation model (93). A polymer-like micelle moves like a

snake in an imaginary tubular-like space generated by

topological restrictions caused by neighboring micellar

aggregates.

It should be mentioned that the lecithin organogel exists

in a rather narrow range of water concentrations. In linear

alkanes, e.g., a homogeneous jelly-like phase is produced

when about 1.5 up to 3.0–3.5 water molecules per lecithin

molecule are added (94). If this amount has been

exceeded, there is a phase separation. At the initial stage

the water addition induces precipitation of a compact jelly-

like phase. With increasing amounts of water, a solid pre-

cipitate is formed. This is widely used in the manufacture

of vegetable oils for their refinement from PLs (see ‘‘No-

menclature, Structure, Sources, Composition, and Process-

ing’’). The process is known as degumming.

Emulsion

The emulsion is a dispersion of one immiscible liquid into

the other. From the thermodynamic point of view it is an

unstable system (67). The role of added surfactants goes

to slow down the kinetics of process (coalescence, floc-

culation, creaming, and Ostwald ripening) that lead to the

emulsion breakdown. Lecithin is believed to be an effec-

tive emulsifying agent (40, 95, 96). It normally brings

about the formation of water-in-oil emulsion because its

HLB (hydrophilic-lipophilic balance) value is of ca. 4

(34, 36). A rather stable emulsion is formed at the oil-to-

water ratio between 0.4 and 0.6 (97). The lecithin con-

centration should be higher than 0.5 wt%. The droplet

3004 Lecithin

diameter varies between 0.005 and 0.015 mm. Lecithin is

capable of stabilizing not only emulsions on the base of

aliphatic and aromatic hydrocarbons, but also fluorocar-

bon-based systems (98, 99); in this case a very stable oil-

in-water emulsion has been found (100) (see also Phar-

maceuticals and Diet Supplements section).

The increased stability of emulsion in the presence of

lecithin is often caused by the formation of a liquid-crys-

talline shell around the droplets (97, 101, 102). The shell

has a multilamellar structure that is caused by the pro-

pensity of lecithin for existing in the La mesophase (Leci-

thin-water section). This keeps effectively droplets from

coalescing, but the liquid crystalline shell cannot exclude

flocculation. Therefore, there is a necessity for additional

stabilization of the emulsion. This can be attained through

lecithin modification, addition of other PLs or surfactants

(see Formulations with phospholipids and surfactants

section for details).

Liquid-crystalline structures

Lecithin in binary mixtures with water exists predomi-

nantly as the lamellar phase La (Fig. 3). It can dissolve

some amounts of nonpolar solvents without a change its

phase state (40, 103, 104). When a critical concentration is

reached, there is a transition to a nonlamellar liquid crys-

talline form (cubic and reversed hexagonal HII phases;

their schematic drawings are shown in Fig. 3). In a case of

n-alkanes, it happens at about 8 wt% (103, 104). The

concentration, at which the phase transition is observed,

depends on the length of an alkane molecule, the fatty acid

residues in lecithin, the amount of water and the tempe-

rature. Higher alkane homologues tend to produce the

effect at larger concentrations (41, 47, 103). Their pene-

tration into the bimolecular layer and arrangement be-

tween hydrocarbon chains leads to an expansion of the non-

polar region, owing to an increased lateral pressure that

destabilizes the lamellar phase. A thermodynamic descrip-

tion of the phase transitions was developed by Gruner et al.

(105–107).

The addition of water into the nonaqueous lecithin

solutions does not include a direct transition into a liquid

crystalline state. The initial system consists of spherical

micelles. The polar additive brings about a change of other

micellar aggregates. In aromatic and chlorinated solvent

one can find swollen micelles. In the rest solvent there is a

transition into the jelly-like state at small water amounts

(Organogel section) and then a precipitation of solid

particles (94, 108). The formation of liquid crystalline

structures takes place at considerably larger water con-

centraions. A whole phase diagram for the lecithin-water-

cyclohexane system has been recently published by An-

gelico et al. (109). Ternary mixtures with other organic

solvent have been still only partially constructed (see, e.g.,

(110)).

Nonaqueus system

It was shown in the Lecithin-organic solvent section that

lecithin can self-organize into various structures in the

organic media or in the presence of organic solvents. This

propensity is retained in the ternary systems. It has not

been studied in sufficient details. One can find fragmen-

tary data in the literature.

Organogels: The addition of formamide, glycerol, or

ethylene glycol into a lecithin solution in alkanes makes

the initial nonviscous solution visoelastic (94, 108). This

phenomenon bears close similarity with that observed for

the water-containing organogels (see Organogel section).

The polar organic solvents induce also the uniaxial growth

of micelles that leads to a formation of polymer-like mi-

cellar aggregates. The micellar shape change is respon-

sible for the transition of nonviscous solution into the

jelly-like state. It was also shown (94, 108, 111) that the

mentioned organic solvents form hydrogen bonds with the

phosphate group in a lecithin molecule. For fairness sake,

it should be pointed out that experiments with polar orga-

nic additives provided a means for developing a molecular

model of polymer-like lecithin micelles. An approach used

was based on a comparison of various organic substances.

It was suggested (94, 112) that the stable polymer-like

aggregates are formed because of linear hydrogen bonding

networks composed of the phosphate groups of lecithin

and solvent molecules that serve as cross-linking (bridg-

ing) agents.

The lecithin organogels prepared by adding formamide,

glycerol, or ethylene glycol demonstrate rheological

behavior that is described in the framework of a Max-

well model (113). This means that the systems are made up

of a three-dimensional network of entangled entities mo-

ving in accordance with the reptation mechanism. It was

shown (113, 114) that the rheological properties of jelly-

like phases depend notably on the nature of the polar

additive. The organic solvents induce the formation of a

tighter network in comparison with water-containing sys-

tems. Furthermore, in their case the relaxation processes

are also faster that is the rearrangement of three-dimen-

sional micellar network formed by lecithin and polar or-

ganic solvents takes less time.

Nonaqueous microemulsion: A ternary microemul-

sion system with water is unknown. It has been found in

a case of ethylene glycol (115, 116). A microemulsion

exists at soybean lecithin concentration of 6–10 wt% in

case the diol content is varied in the range of 30–80 wt%.

After mixing all the components, droplets 100–150 nm in

diameter were formed. The nonaqueous system demons-

L

Lecithin 3005

trated limited stability. The authors observed a phase

separation with time.

Multicomponent Mixtures

Lecithin is widely used in numerous formulations, in-

cluding human and animal nutrition, medicine, cosmetics,

and a variety of industrial applications. They are normally

made up of more that three components. Because the for-

mulation are many and varied, it is impossible to list all of

them. Here will be considered only the main approaches

to the development of such practically important systems

as microemulsion and rules for mixing lecithin with PLs

and surfactants. At the end, lecithin-polymer complexes

are discussed.

Microemulsions

The microemulsion, as defined by Danielsson and Lindman

(117), is a homogeneous, optically isotropic and ther-

modynamically stable liquid solution. Because the diame-

ter of droplets of one liquid in another is usually in the

range of 1–10 nm (118), it is transparent or slightly opales-

cent. Lecithin is not, unfortunately, among the surfactants

that are able to stabilize microemulsion system alone. It

can be made, if a third solvent (co-solvent) or an additional

surfactant (co-surfactant) is additionally introduced.

Shinoda with collaborators were the pioneer investi-

gators who studied systematically a microemulsification

in oil-water mixtures in the presence of lecithin (119–

121). They found that a microemulsion was formed in a

soybean lecithin-water-hexadecane system with the addi-

tion of lower alcohols, ethanol, or propanol. The amount

of propanol was increased, as shown in Backlund and

Rantala (122), with changing hexadecane to dodecane,

The microemulsion formation was also observed in the

presence of triglycerides taken instead of alkane (123). It

was accompanied by a sharp decrease in the interfacial

tension (up to 4�10�4 mN/m at the oil/water interface

(124)). The microemulsification was strongly dependent

of the molecular weight of aliphatic alcohols. For in-

stance, a system with swollen micelles was found in place

of the microemulsion, once propanol was substituted

for butanol (119). On the other hack, n-butanol, sec-bu-

tanol, and iso-butanol were suited to form a microemul-

sion in the presence of isopropymyristate as the oil com-

ponent (125).

The useful recommendations for the preparation of le-

cithin-containing microemulsions have been developed by

Kahlweit et al. (126). They are the following. 1) When

lecithin is taken with shorter hydrocarbon chains, the

hydrophobicity (lipophilicity) of co-solvent or co-surfac-

tant should be increased; e.g., propanol can be substituted

for butanol. The needed effect in some instances can be

achieved by mixing of co-solvents (propanol with butanol

or butanol with pentanol). In this case, the hydropho-

bicity/hydrophilicity is changed in a delicate manner. 2)

The lower homologue of n-alkane, the less hydrophobic

co-solvent or co-surfactant should be taken. An example

is the following. By substituting hexadecane for hexane,

one should use ethanol in place of propanol. What is also

important, higher n-alkanes favor the microemulsification

of naturally occurring lecithins.

It was also suggested by Kahlweit et al. (127) to re-

place the aliphatic alcohols for less toxic 1,2-alkanediols.

Thus, propanol is successfully substituted for 1,2-pen-

tanediol in system containing soybean lecithin. This is in

agreement with observation made by Aboofazeli et al.

(128) who took isopropylmyristate was taken as the oil

phase. It was also shown that the lecithin microemulsions

could be prepared by addition of various co-surfactants

including fatty acids, polyethylene glycol alkyl ethers, or

alcohols. The effect of sugar-containing surfactants and

sodium taurocholate on the formation of lecithin micro-

emulsions were thoroughly studied by Voncorswant et al.

(129). The examined systems can be of interest for use in

cosmetics, pharmacology, etc. (130).

Formulations with phospholipids and surfactants

Lecithin is widely used in numerous formulations as the

emulsifier. Therefore, lots of studies are devoted to its

emulsifying properties. PLs and surfactants are the main

additives that are used to modify the emulsifying ability

of lecithin. Its stabilizing effect is often attributed to a

liquid-crystalline shell formed around the droplets (58, 97,

101, 102). This is enough to prevent them from the coa-

lescence, but processes such as flocculation and creaming

cannot be excluded. The effective way to do this is through

an introduction of PLs or surfactants. Their addition can

also lead to a change of the emulsion type. This has also

many uses.

If a formulation for food, cosmetic, or pharmacology is

developed, which are cases where it is desirable to hold

the lecithin biocompatibility, the best solution is to resort

to PLs. Their diversity provides various opportunities for

changing the stability and type of an emulsion.

The addition of PLs has various effects on the emul-

sifying ability of lecithin (40, 95–97, 131); e.g., phospha-

tidylethanolamine (Fig. 1), which is prone for the forma-

tion of reversed hexagonal phase (47, 48), enables one to

prepare a water-in-oil emulsion. The presence of lysoleci-

thin possessing only one hydrocarbon chain has an oppo-

site effect, i.e., a transition to an oil-in-water emulsion.

Anionic PLs, phosphatidic acid, phosphatidylserine, and

phosphatidylinositol (Fig. 1), provide a better stabilization

3006 Lecithin

of emulsions that neutral additives. Their effect is related

to the additional repulsive electrostatic forces. As shown

by Davis and Hansrani (132), the anionic PLs demonstra-

ted various efficacies. The most stability of oil droplets to

the coalescence in model experiments was observed for

mixtures of lecithin with phosphatidic acid. The least sta-

bilizing effect was found for phosphatidylinositol.

All the PLs mentioned above are widely used to im-

prove or change the lecithin functionality by mixing or

blending with it (19, 23, 34, 35, 133). Such mixtures or

blends are called compounded lecithins by manufacturers.

It should be pointed out that the crude lecithin is a mixture

of various PLs (see ‘‘Nomenclature, Structure, Sources,

Composition, and Processing’’). To modify its emulsify-

ing properties, it is subjected to fractionation and puri-

fication (22, 34) as well as modification through chemical

and enzymatic procedures (19–21, 34, 133). The manu-

facturers suggest numerous products including mixtures

with different lecithin content, with modified lecithins

and with various PLs.

Synthetic surfactants are also widely used as modified

additives to lecithin formulations or as agents providing

solubilization of PLs of the biological membranes. The

action of such surfactants as sodium dodecylsulfate, salts

of fatty acids, bile salts, cetyltrimethylammonium bro-

mide, dodecyltrimethylammonium chloride, dodecyl-N-

betaine, octyl glucoslide, p-t-alkylphyenyl polyoxyethy-

lene ethers and alkyl polyoxyethylene ethers have been

studied in sufficient details (134–139). The effect pri-

marily depends on their molecular shape and to a lesser

degree on their charge. The single-chain surfactants per-

form at their best. When they are added into an aqueous

solution containing lecithin vesicles, one can observe dis-

integration of the lamellar structure (134–139). This re-

sults in a formation of mixed micelles.

The vesicle-to-micelle transition proceeds, as origi-

nally believed (134–136), through three stages. Detailed

studies have revealed that most of the systems demon-

strate more complicated behavior (137, 138). In all in-

stances the initial portions of surfactant, when added, are

absorbed almost entirely by the lecithin lamellae. The

process is characterized by a rapid kinetics (140). The ab-

sorbed surfactants every so often induce a vesicle growth.

This behavior is typical for many substances. It was ob-

served in a case of ionic (alkyl sulfates (141, 142), alkyltri-

methylammonium bromide/chloride (143–145)), zwitter-

ionic (dodecylbetaine (146)) and nonionic (octyl glycoside

(147, 148), octaethylene glycol n-dodecyl monoether

C12E8 (149) and Triton X-100 (150)) surfactants. It

should be pointed out that in the case of ionic substances

this behavior was found in the presence of inorganic

electrolyte (0.10–0.15 M NaCl). In its absence long-

chain alkyltrimethylammonium chlorides and alkyl sul-

fates did not induce vesicle growth (137, 138, 144, 149). A

study on the effects produced by cetyltrimethylammonium

chloride with the help of cryo-transmission electron

microscopy, small angle x-ray diffraction, and 2H and31P NMR revealed a smooth transition from lamellar to

micellar state through an intermediate state representing a

perforated (defected) lamellar structure (137, 138, 143,

144, 150). The transition into the micellar state commen-

ces when a saturation of lamellae with the absorbed sur-

factants is achieved (135, 139). It normally happens as the

molar ratio of surfactant to lecithin varied between 1 and

2. In addition, the surfactant concentration should exceed

the cmc (134, 135).

The vesicle-to-micelle transition can proceed through

various intermediate stages. The simple three-stage

scheme is the case for alkyl sulfate with a short hydro-

carbon chain (142) and dodecyltrimethylammonium chlo-

ride (144). This involves the vesicle growth as a result of

the surfactant absorption, the formation of mixed micelles

coexisting with vesicles, and in the closing stage the com-

plete disappearance of vesicles. Complicated phase beha-

vior is more common to lecithin-surfactant mixtures (137,

138). The vesicles can transfer gradually into micelles.

Sometimes, as observed in a case of octylglucoside (147),

it proceeds through phase separation. At rather large con-

centrations the mixing of lecithin with octylglucoside

(147, 151) or dodecylmaltoside (152) led to a jelly-like

state. The phenomenon is caused, as shown by means of

cryo-transmission electron microscopy (152), by the for-

mation of polymer-like micelles. Comprehensive conside-

ration of the phase behavior in lecithin-surfactant sys-

tems have been given in recent review articles by Almgren

(137, 138).

The mixed micelles can take various morphology and

shape ranging from sphere to cylinder (134, 135, 137–

139). It is possible to find polymer-like micellar aggra-

gates not only in the presence of alkylglucosides, as men-

tioned above, but also in aqueous solutions of lecithin

with bile salts (153), alkyltrimethylammonium bromide/

chloride (144, 154), and sodium dodecylsulfate (142). The

micellar shape and transformation strongly depend on the

molar ratio between lecithin and surfactant, their hydro-

carbon chain length, and presence of electrolytes. In ac-

cordance with a developed model by Fattal et al. (155),

the shape of mixed micelles is determined by a ratio

between sizes of head groups and hydrocarbon chains

in molecules.

Polymer-lecithin complexes

Polymers have various effects on the colloid behavior of

lecithin. A well-known example is poly(ethylene-oxide).

L

Lecithin 3007

Its addition is used to cover the surface of lecithin vesicles,

thus producing ‘‘stealth’’ vesicles having the increased

blood circulation time (56). The same steric stabilization

can be achieved by introducing triblock copolymers of

poly(ethylene oxide)-poly(propylene oxide)-poly(ethy-

lene oxide) type (156–158). It should be mentioned that

poly(ethylene oxide)polymers, of which the molecular

weight ranges between 1000 and 18,500, induce an aggre-

gation and fusion of vesicles (159). The effect is caused, as

shown by Kuhl et al. (160), by a depletion attraction due to

an osmotic force in the gap between vesicles, arising by

virtue of decreased polymer concentration. The steric bar-

rier is formed when poly(ethylene oxide) of a higher mole-

cular weight (> 18,500) is applied. The polymer adsorbs

sufficiently strong on the vesicle surface to exceed the re-

pulsion from the gap between vesicles. It has been shown

that the stabilizing effect could be realized by introducing

poly(vinyl alcohol) and its copolymers (161), hyaluronic

acid (162), and poly(acrylic acid) and carboxymethylchi-

tin (163). The vesicles also can be stabilized by placing

them into a polysaccharide hydrogel (164). Their stability,

as found in (165), depends on the polysaccharide type. For

example, carboxymethylcellulose did not modify the ve-

sicle properties, while a leakage of vesicle-entrapped subs-

tances was observed in a xanthan gum hydrogel.

The addition of polymers bearing positive charges (po-

lyelectrolytes) into aqueous solutions of lecithin vesicles

can induce a phase separation. The complexes thus preci-

pitated have been prepared by using poly(diallyldimethyl-

ammonium chloride) (166) and poly-l-lysine (167). Le-

cithin maintains its multilameller structure (Fig. 3), while

polyelectrolytes reside between lamellae, interacting elec-

trostatically with the polar groups of lecithin molecules.

It was suggested (166, 168–170) that the structure of

formed complexes of lecithin with poly(diallyldime-

thylammonium chloride) can be represented with the

help of an ‘‘egg-carton’’ model by Goetz and Helfrich

(171). The lamellae in this model have an undulated

structure that resembles stacked egg cartons. A peculiarity

of the lecithin-poly-l-lysine complex is a helix conforma-

tion of polypeptide (167). Its molecules possessing a

rodlike shape are oriented parallel to each other in the

interlamellar layers.

Anionic polysaccharides (chondroitin sulfate, heparin,

dextran sulfate, b-cyclodextrin sulfate, carboxymethyl-

dextran, and hyaluronic acid) could also induce phase se-

paration when they were added in a solution of lecithin

vesicles (172, 173). A supramolecular structure has been

found in systems with hyaluronan (glycosaminoglycan)

(174). The polysaccharide led to the rearrangement of the

vesicles into huge perforated membrane-like structures

and cylinders 12 nm in diameter.

The lecithin-polyelectrolyte complexes demonstrate

interesting mechanical, optical, and dielectric properties

(169, 170, 175), which have not been so far studied in

sufficient details. These complexes, of which the multi-

lamellar structure is stabilized by incorporated polymers,

can provide a basis for preparing a new class of mesomor-

phous lecithin materials.

USES

The greatest part of lecithin is used in foods, primarily in

margarine, 25–30%, and baking, confectionery and ice

cream, 25–30% (23). Nonfood use does not exceed most

likely 30% (36). This includes animal feed, cosmetics, and

soaps; pharmaceuticals, paints, and coatings; inks, poly-

mers, pesticides, petroleum, and fuel products; textiles, and

many others (23, 36). The numerous applications of leci-

thin are caused with its proper colloid properties and broad

range of functional benefits. They are listed in Table 4. In

the following consideration, lecithin usage is divided into

food, animal feed, and nonfood applications.

Food

Lecithin usage in food applications is based on most of the

lecithin functionalities. Their set is changed in each par-

ticular case, which is determined by the food type, ingre-

dients, and physical and colloidal state. Only one function

is used almost for all food products and that is the emul-

sification. The food use of lecithin is caused, as confirmed

by the World Health Organization, by its safety. The FDA

has awarded GRAS status, which means generally that it is

recognized as safe (CFR No. 182.1400/184.1400).

Margarine

Lecithin is applied in the combination with monoglyce-

rides for the stabilization of water-in-oil emulsion. Its ad-

dition causes better wetting of fat crystals by oil and water

(176). It is also antispattering and browning agent. The

important function is a control over crystallization pro-

cesses (5, 34). Its addition improves frying properties and

spreadability.

Baking goods

Lecithin, added in amounts of 0.1–1.0wt%, is applied for

improvement of processing, production quality, and con-

sumer acceptance of baking products through emulsifica-

tion, stabilization, wetting, and conditioning (34, 133, 177).

In cookies, crackers, and extrusion products, the lecithin

addition facilities mixing and machinability, modifies the

consistency and texture through promoting fat distribution

and shortening action, and increases the dryness, flavor

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Lecithin 3009

stability, and shelf life. It functions more effectively as a

release agent than the animal or vegetable oils, owing to a

modification of the solid release surfaces of oven con-

veyers, flame broiling, etc., reducing product sticking and

breakup as well as facilitating clean-up (34, 133, 177).

Furthermore, lecithin prevents the oxidation of animal and

vegetable oils (178). It is suggested as fat reducer (23).

Confectionery

Lecithin usage (0.2–1.0wt%) provides a better wetting,

mixing, emulsification, emulsion stabilization, homoge-

nous fat distribution, conditioning, and antisticking ef-

fects. For the chocolate production, of major importance is

a viscosity decrease. Owing to this effect, the addition of

0.5% lecithin enables a manufacturer to save the most

costly ingredient, cocoa butter (as much as 5%), process-

ing time, and energy (179, 180). Its presence in candy, car-

amels, chocolate nougats, etc. positively influences eating

properties, appearance, and shelf life (23, 179).

Ice cream and whipped toppings

This kind of product falls in frozen foams. Lecithin is ad-

ded in amounts of 0.15–0.5% to provide foam formation as

well as emulsification, stabilization, and smoothness. It al-

so counteracts sandiness in storage. The particular function

is to control over-crystallization processes. The positive

effect of lecithin is manifested in producing altered crystal

sizes and structure that improves the product texture and

viscosity (34).

Instant foods

Lecithin (0.5–3.0%) is used in many instant powders

including cocoa, coffee, drinks, toppings, coffee white-

ners, milk replacers, cake mixes, puddings, and powdered

soups. It serves as a wetting agent, making particles easily

soluble or dispersed. Its addition often aids in the control

over the rate of moisture absorbance and penetration by

hygroscopic powders (34). Furthermore, they can be more

quickly and easily mixed (133). After transferring pow-

ders into the dispersed or solubilized state, lecithin per-

forms stabilizing functions (23).

Oils and fats

The improvement of operational functionalities of fats

and oils is achieved by introducing lecithin (0.01–2%) as

an emulsifier, wetting agent, and antioxidant. This has se-

condary effect such as the decreased cloud point of vege-

table oils, increased spreadability, improved stability, and

extended shelf life (5, 23). The lecithin addition also

makes for better release properties. Moreover, specially

formulated products are available for the industrial and

household use as bakery depanning agents, griddle fray-

ing fats, sprays, aerosols, and nonaerosols to solve any

one of release problems (34, 133).

Animal Feed

Animal feed includes domestic animal, pet, fur-bearing ani-

mal, and fish foods and nutritional supplements. Lecithin

is used as an emulsifier, wetting, dispersing, and condition-

ing agents. Furthermore, its addition in animal foods is

recommended as a source of energy, choline, organically

combined phosphorus, and unsaturated fatty acids (181).

Nonfood Use

Lecithin multifunctionality is the basis, as in the cause of

foods, for many industrial and home applications (see

Table 4). Because of its biodegradability, lecithin holds an

advantage over many surfactants. Major nonfood users

are the paint and coating industry. Next are pharmaceuti-

cals, diet supplements, inks, and cosmetics (36).

Paints, inks, and coatings

Waxes, polishes, and wood preservatives are also among

these products. Lecithin (0.5–5% of pigment) is useful as

a wetting, mixing, dispersing, emulsifying, suspending,

and stabilizing agent. It is successfully applied both for the

oil- and water-based formulations. Its presence saves time

in grinding and mixing, efficiently prevents pigments from

hard setting out during storage and facilitates redispersion

after storage (182). Lecithin eliminates excessive paint on

the surface (flooding), paint flow downward (sagging), co-

lor change with drying and appearance of parallel hairlike

striation (silking). In addition, paints have increased cov-

ering power and brush with the minimum of effort (182).

In water-based formulations lecithin provides addition-

ally thickening and spreading effects. It demonstrated a

corrosion protection on steel surfaces. Polymer coating of

food containers have improved release properties (36).

Pharmaceuticals and diet supplements

Lecithin is a component of biological membranes and in-

volved in many biological processes, which explains why

it is widely applied as a therapeutic agent and dietetic

supplement. It is a needed source of diacylglycerol, cho-

line, and fatty acids for humans and animals. A choline-

deficient diet causes, as well documented (36, 183, 184),

an accumulation of triglycerides in the liver that leads to

fatty infiltration. Choline deficiency promoted also car-

cinogenesis in experimental animals (183, 184). In humans

it brought about changes suggestive of modest hepatic

dysfunction and subtle abnormalities in muscles function

3010 Lecithin

(184). Many studies have demonstrated that administration

of lecithin lowers cholesterol in the blood that might be

helpful for patients with cardiovascular diseases (36, 185,

186). To treat it and protect the liver, on the market there

are, respectively, Lipostabile and Essentialle, which

contain high amounts of lecithin with unsaturated fatty

acid residues (23). A diet with an increased lecithin level

has enhanced the energy, appetite, and alertness of dogs

and cats (181). One can find lots of publications on the

possible beneficial effects of lecithin on the certain di-

seases of the nervous system (Alzheimer’s, tardive dys-

kinesia), owing to the presence of choline in its molecule.

It is partially related to acetylcholine, which plays an

essential role in the transmission of nerve impulses. How-

ever, definitive evidence of the memory improvement

after intensive lecithin administration has not been pro-

vided, although there have been reports about successful

results (183, 185, 187).

Pharmaceutical applications of lecithin are also based

on its traditional functions including emulsification,

wetting, dispersing, and stabilization (36). It is used ra-

ther widely for preparing emulsions for parenteral nutri-

tion and drug delivery (188). Fluorocarbon emulsions re-

present a special case for the intravenous administration

as a blood substitute (antihypoxic agent) for oxygen and

drug delivery (98). To improve the stability and delivery

properties of emulsions, melt-emulsified nanoparticles

have been developed that can be imagined as an emulsion

with the solid core (usually triglycerides) formed by cool-

ing (189). As a promising system for parenteral, ocular,

peroral, and percutaneous administration is considered a

microemulsion (190). Liposomes represents a well-known

tool for various pharmaceutical applications (56, 191–

193). They are used to solubilize drugs, protect them, pro-

vide sustained release, improve targeting, and enhance pe-

netration (56).

Cosmetics and soaps

Lecithin (0.5–5.0%) can be found in all kinds of creams,

shampoos, liquid and bar soaps, lotions, hair condition-

ers, bath oils, face powder, lipstick, and nail enamels

(194). Its common functionalities are a wetting, conditio-

ning, softening, and penetrating agent, emulsifier, disper-

sant, stabilizer, emollient, moisturizer, and antioxidant. At

present lecithin is often introduced in creams in the form

of liposomes, which are especially useful to provide a

prolonged moisturizing effect and selective and sustained

release of biologically active ingredients (23, 36, 195). It

is worth mentioning the improvement of ‘‘skin feel,’’

color stability and adhesion to the skin, and the decrease

of undesirable oily or greasy feeling of cosmetics after the

addition of lecithin (196).

Petroleum products

Lecithin (0.005–2.0%) serves as an emulsifier, detergent,

antioxidant, anticorrosive, lubricating, and antiwearing

agent in gasoline, fuel oils, greases, and lubricating and

cutting fluids (23, 36). It helps to disperse powdered coal

and water in the oils. The former then demonstrated en-

hanced stability in time, and the latter burned with a dec-

reased emission (ca. 30%) of nitrogen oxides (36).

Textiles

Lecithin (0.2–0.5%) functions as an emulsifying, wetting,

softening, and conditioning agent. It allows improvement

of hydrophilicity of cotton and reduction of stickiness of

cellulose fibers and provides a spinning lubrication effect

for cotton and wood (36). A spray including lecithin is

used to reduce cotton dust (23, 36).

Polymers

Lecithin is added to disperse pigments, prepare polymer

products with modified characteristics and extended func-

tionalities, and improve release properties (23, 36). It is

also applied in polymer coatings (food containers, sausage

casing coatings, stocking nets for hams and other meats,

etc.) and processing (coating of molds) as a release agent

(182).

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