Properties of Lecithin tested for its standarization

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Commercial lecithins (mixtures of phospholipids) are available in several physical states. Commercial lecithin can be produced as an oily liquid (lecithin + vegetable oil), a powder (deoiled lecithins) or water emulsion. Powder form is obtained by treatment oily lecithin by the alcohol or acetone. The powdered lecithins grades consist of a mixture of isolated phospholipids which have either granular or powdered forms. The consistency of alcohol-fractionated lecithins depends on the phosphatidylcholine/phosphatidylethanolamine ratio, which in turn depends on the polarity of the alcohol used, the ratio of lecithin to alcohol, the temperature, and the extraction time. Water emulsions of lecithin are produced by dissolving powder lecithins in water solutions.

Their chemical - physical properties are unique to the individual products and depends of concentration and content of phospholipids, mainly: Phosphatidylcholine (PC) and Lysophosphatidyl- choline (LPC), Phosphatidylethanolamine (PE) and Lysophos- phatidylethanolamine (LPE), N-Acyl-phosphatidylethanolamine (N-Acyl-PE), Phosphatidylinositol (PI), Phosphatidic Acid (PA), as well as polar lipids, mainly glycolipids (e.g..glycosylglycerides, sterolglycosides and esteri- fied sterolglycosides) and other components. All of above compounds can have different fatty chains (depends of the source of the lecithin) as well.

 

Analytical and Test Methods List

The standard methods of analysis for commercial lecithin (the Official and Tentative Methods of the American Oil Chemists' Society) with AOCS and DGF numbers:

AI - Acetone-Insoluble matter (Ja 4-46, F-I 5)

TI - Toluene-Insoluble matter (F-14b)

HI - Hexane-Insoluble matter (Ja 3-87)

Clarity

Moisture KF - The Karl Fischer method (Ja 2b-87, F-I 4)

Moisture (Ja 2a-46)

AV - Acid value (Ja 6-55, F-I 3)

POV - Peroxide value (Ja 8-87, F-I 3b)

Gardner color (Ja 9-87, C-IV 4a)

Viscosity (rotation) (Ja 10-87, F-I 2a)

Viscosity (bubble) (Ja 11-87)

IV - Iodine value (Cd 1-25)

Total Phosphorous (Ja 5-55)

TLC (Ja 7-86)

HPLC-UV (Ja 7b-91)

HPLC-LSD (Ja 7c-07, F-I 6a)

HPTLC (F-I 6)

Iron (Ca 15-75 F-I 4a)

Fatty acids content

Solubility in vegetable oil

Dispersability in water

 

Analytical and Test Methods short description

AI method determines the acetone-insoluble matter under the conditions of the test, free from sand, meal, and other petroleum ether-insoluble material. Commercial lecithins are mainly composed of phospholipids (ca. 66 %); the other major components are nonphospholipid compounds such as triglycerides. Since phospholipids are insoluble in acetone, and triglyceride is soluble in acetone, the amount of acetone-insoluble material in lecithin corresponds approximately to the phospholipid content.

HI indicates the amount of residual fiber which originates from the production process. The HI measurement is the official Foods Chemicals Codex test method. The HI value must be suppressed to 0.1 %. A high HI level indicates a low grade of lecithin.

Clarity depends of moisture content and residual fibers. High-clarity lecithin can be produced by oil filtration to give HI levels of nearly zero and thin-layer drying process.

AV is the number of milligrams of potassium hydroxide necessary to neutralize the acids in one gram of sample. The acid value is the phospholipid index number.

PV is the number of milliequivalents of peroxide per 1000 grams of sample, which oxidize potassium iodide under the conditions of the test. The oxidizing substances are generally assumed to be peroxides or other similar products of fat oxidation.

Moisture KF method determines the actual water content of lecithin by titration with Fischer reagent which reacts quantitatively with water. The moisture content of lecithin products is typically less than 1.5 %.

Gardner color method determines lecithin color by comparison of an undiluted sample to standards of a specified color. Although the major constituents of lecithin are colorless, the color of commercial lecithin is red-brown or dark-red. The colored components include carotenoid pigments and pigments formed by reaction of amino compounds with phosphatide sugars (Maillard reaction). PE also contributes to the color through formation of aldol products. The bleaching method is treatment with hydrogen peroxide or benzoyl peroxide.

Viscosity (rotation) determines Brookfield viscosity in mPa(=cP) of a fluid lecithin at a specified temperature. The viscosity of fluid lecithin is decreased by addition of fatty acids.

Viscosity (bubble) determines viscosity of transparent liquids by bubble time.

IV is a measure of the unsaturation of fats and oils and is expressed in terms of the number of centigrams of iodine absorbed per gram of sample (% iodine absorbed).

TLC ia a analysis of phospholipid in lecithin concentrates and is performed by fractionation with two-dimensional thin-layer chromatography 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.

HPLC-UV is used for the direct determination of single phospholipids PE, PA, PI, PC in lecithin by high performance liquid chromatography. The method is applicable to oil-containing lecithins, deoiled lecithins, lecithin fractions, but not applicable to lyso-PC and lyso-PE.

Solubility of the lecithin depends of its composition. Lecithin is soluble in oils and is hydrated in water, in which it disperses with formation of an emulsion.

SolventWaterAlcoholAcetone
Lecithin/Phospholipid type   
Soybean lecithininsolublesolubleinsoluble
PCsolublereadily solublesparingly soluble
PEreadily solublesolubleinsoluble
PIreadily solubleinsolubleinsoluble

 

General specifications for standard lecithins

Not all properties of lecithins are included in specifications for standard lecithins. There can be small differences in specifications between countries and regions (see table below).

Specification

Standard

 

FAO/WHO, 8431

FCC, 182 and 1400

EEC, E 332

Japan

Acid value

25 – 35

36

45

40

Benzene insoluble, %

 0.3

 0.3

 

 0.3

Acetone insoluble, %

62

50

60

40

Peroxide value, meq/kg (max)

10

 

10

10

Heavy metals, ppm

40

40

40

20

Arsenic, ppm

 3

 3

 3

 4

Weight loss on drying, %

 2

 1.5

 2

 2