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Prepared at the 28th JECFA (1984), published in FNP 31/2 (1984) and in FNP 52 (1992) |
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SYNONYMS |
INS No. 440 |
DEFINITION |
Pectin consists mainly of the partial methyl esters of polygalacturonic acid and their sodium, potassium, calcium and ammonium salts. It is obtained by aqueous extraction of appropriate edible plant material, usually citrus fruits or apples. No organic precipitants shall be used other than methanol, ethanol and isopropanol. In some types a portion of the methyl esters may have been converted to primary amides by treatment with ammonia under alkaline conditions. The commercial product is normally diluted with sugars for standardization purposes, and mixed with suitable food-grade buffer salts reuired for pH control and desirable setting characteristics. The article of commerce may be further specified as to pH value, jelly strength, viscosity, degree of esterification, and setting characteristics. |
C.A.S. number |
9000-69-5 |
DESCRIPTION |
White, yellowish, light greyish or light brownish powder |
FUNCTIONAL USES |
Gelling agent, thickener, stabilizer |
CHARACTERISTICS | |
IDENTIFICATION | |
Solubility |
Soluble in water forming a colloidal, opalescent solution; insoluble in ethanol |
Gel formation by heating |
Heat 1 g of the sample with 9 ml of water on a steam bath until a solution is formed. Replace water lost by evaporation. A gel is formed upon cooling |
Gel formation |
To 5 ml of a 1-in-100 solution of the sample add 1 ml of 2 N sodium hydroxide and allow to stand at room temperature for 15 min. A translucent to opaque gel or semi-gel is formed |
Precipitate formation |
To a 1-in-100 solution of the sample add an equal volume of ethanol. A translucent, gelatinous precipitate is formed
Acidify the gel from the Gel formation test with dilute hydrochloric acid TS and shake well. A voluminous, colourless, gelatinous precipitate forms, which upon boiling becomes white and flocculent (pectic acid). |
Test for amide group |
Add 2 ml of hydrochloric acid and 50 ml of 60% ethanol to 0.5 g of the sample, and stir well for 20 min. Transfer to a fritted glass filter tube wash with six 10 ml portions of the HCl-60% ethanol mixture. Dissolve in 100 ml distilled water; it may be necessary to add a few drops 0.1 N NaOH to achieve solution. Transfer 4 ml of this solution into a test tube (recommended dimensions 15.5 mm inner diameter and 146 mm length). Add 1 ml 5 N NaOH and mix. The mixture will form a gel. Fill a small glass tube (recommended dimensions 7.8 mm inner diameter and 89 mm length) with 2.5 ml boric acid TS and let glide into the test tube. Close with parafilm and incubate overnight at 30o. In case of presence of amide groups the indicator changes its colour from red to green, due to release of ammonia. |
PURITY | |
Loss on drying |
Not more than 12% (105o, 2 h) |
Sulfur dioxide |
Not more than 50 mg/kg See description under TESTS |
Methanol, ethanol and isopropanol |
Not more than 1% singly or in combination See description under TESTS |
Acid-insoluble ash |
Not more than 1% |
Nitrogen content |
Not more than 2.5% after washing with acid and ethanol |
Galacturonic acid |
Not less than 65% calculated on the ash-free and dried bases See description under TESTS |
Degree of amidation |
Not more than 25% of total carboxyl groups of pectin See description under TESTS |
Copper |
Not more than 50 mg/kg |
Zinc |
Not more than 25 mg/kg |
Arsenic |
Not more than 3 mg/kg (Method II) |
Lead |
Not more than 10 mg/kg |
TESTS | |
PURITY TESTS | |
Sulfur dioxide |
Suspend 100 g of the sample in 500 ml of methanol in a 1000-ml round-bottom flask, which is provided with a gas inlet tube reaching almost the bottom and connected to the neck with a reflux condenser. Prepare a glass joint connection from the condenser to an absorption flask or U-tube containing 10 ml of 3% H2O2 solution neutralized to methyl red TS. Connect the gas inlet tube with an oxigen-free source of CO2 or N2, and maintain a gas stream so as to cause steady bubbling. As soon as the apparatus is flushed free of air, pour 30 ml of HCl solution (10 ml conc. HCl + 20 ml H2O) into the reflux condenser, and immediately connect the absorption flask or U-tube. Heat slowly until methanol starts refluxing, and reflux gently for 2 h. Disconnect the apparatus and titrate the H2O2 solution against methyl red TS with 0.01 N NaOH. Each ml of 0.01 N NaOH corresponds to 0.32 mg of SO2. |
Galacturonic acid, Degree of amidation, Degree of esterification, Degree of acetate ester |
Weigh 5 g of the sample to the nearest 0.1 mg, and transfer to a suitable beaker. Stir for 10 min with a mixture of 5 ml of hydrochloric acid TS, and 100 ml of 60% ethanol. Transfer to a fritted-glass filter tube (30 to 60 ml capacity) and wash with six 15-ml portions of the HCl-60% ethanol mixture, followed by 60% ethanol until the filtrate is free of chlorides. Finally wash with 20 ml of ethanol, dry for 2.5 h in an oven at 105o, cool and weigh. Transfer exactly one-tenth of the total net weight of the dried sample (representing 0.5 g of the original unwashed sample) to a 250-ml conical flask and moisten the sample with 2 ml of ethanol TS. Add 100 ml of recently boiled and cooled distilled water, stopper and swirl occasionally until a complete solution is formed. Add 5 drops of phenolphthalein TS, titrate with 0.1 N sodium hydroxide TS and record the results as the initial titre (V1).
Add exactly 20 ml of 0.5 N sodium hydroxide TS, stopper, shake vigorously and let stand for 15 min. Add exactly 20 ml of 0.5 N hydrochloric acid TS, and shake until the pink colour disappears. Titrate with 0.1 N sodium hydroxide TS to a faint pink colour which persists after vigorous shaking; record this value as the saponification titre (V2).
Quantitatively transfer the contents of the conical flask into a 500-ml distillation flask fitted with a Kjeldahl trap and a water-cooled condenser, the delivery tube of which extends well beneath the surface of a mixture of 150 ml of carbon dioxide-free water and 20.0 ml of 0.1 N hydrochloric acid TS in a receiving flask. To the distillation flask add 20 ml of a 1-in-10 sodium hydroxide solution, seal the connections, and then begin heating carefully to avoid excessive foaming. Continue heating until 80-120 ml of distillate has been collected. Add a few drops of methyl red TS to the receiving flask, and titrate the excess acid with 0.1 N sodium hydroxide TS, recording the volume required, in ml, as S. Perform a blank determination on 20.0 ml of 0.1 N Galaturonic acid hydrochloric acid TS, and record the volume required, in ml, as B. Degree of amidation Record the amide titre (B-S) as V3.
Transfer exactly one-tenth of total net weight of the dried sample (representing 0.5 g of the original unwashed sample) and wet with about 2 ml ethanol in a 50-ml beaker. Dissolve the pectin in 25 ml 0.125 M sodium hydroxide. Let the solution stand for 1 h with agitation at room temperature. Transfer quantitatively the saponified pectin solution to a 50-ml measuring flask and dilute to the mark with distilled water. Transfer 20.00 ml of the diluted pectin solution to a distillation apparatus and add 20 ml of Clark's solution, which consists of 100 g of Magnesium sulfate heptahydrate and 0.8 ml of concentrated sulphuric acid and distilled water to a total of 180 ml. This apparatus consists of a steam generator connected to a round-bottom flask to which a condenser is attached. Both steam generator and round-bottom flask are equipped with heating mantles.
Start the distillation by heating yp the round-bottom flask containing the sample. Collect the first 15 ml of distillate separately in a measuring cylinder. Then start the steam supply and continue distillation until 150 ml of distillate have been collected in a 200-ml beaker. Add quantitatively the first 15 ml distillate and titrate with 0.05 M sodium hydroxide to pH 8.5 and record volume required, in ml, as S.
Perform a blank determination on 20 ml distilled water. Record the required volume, in ml, as B. Record acetate ester titre (S-B) as V4
Calculate degree of esterification (as % of total carboxyl groups) by the formula:
Calculate degree of amidation (as % of total carboxyl groups) by the formula:
Calculate degree of acetate ester (as % of total carboxylic groups from galacturonic acid) by the formula:
Calculate mg of galacturonic acid by the formula:
The mg of galacturonic acid obtained in this way is the content of one-tenth of the weight of the washed and dried sample. To calculate % galacturonic acid on a moisture-and-ash-free basis, multiply Galaturonic acid the number of mg obtained by 1000/x, x being the weight in mg of the Degree of amidation washed and dried sample. |
Methanol, ethanol and isopropanol |
Principle:The alcohols are converted to the corresponding nitrite esters and determined by headspace gas chromatography.
Sample preparation:Dissolve 100 mg of sample in 10 ml of water using sodium chloride as a dispersing agent if necessary.
Internal standard solution:Prepare an aqueous solution containing 50 mg/l of n-propanol.
Standard alcohol solution:Prepare and aqueous solution containing 50 mg/l each of methanol, ethanol and isopropanol.
Procedure:Weigh 200 mg of urea into a 25-ml "dark vial" (Reacti-flasks, Pierce, Rockford 3, USA or equivalent). Purge with nitrogen for 5 min and then add 1 ml of saturated oxalic acid solution, close with a rubber stopper and swirl. Add 1 ml of sample solution, 1 ml of internal standard solution and simultaneously start a stop watch (T=0). Swirl the vial and recap with an open screw cap fitted with a silicone rubber septum. Swirl until T=30 sec. At T=45 sec inject through the septum 0.5 ml of an aqueous solution of sodium nitrite (250 g/l). Swirl until T=70 and at T=150 sec withdraw through the septum 1 ml of the headspace using a pressure lock syringe (Precision Sampling Corp., Baton Rouge, Louisiana, USA or equivalent).
Gas chromatography:Insert syringe needle in the injection port; pre-compress the sample, then open the syringe and inject the sample. Use the following conditions:Column: - length: 90 cm - diameter: 4 mm - material:glass - packing: first 15 cm packed with chrompack (or equivalent) and the remainder with Propak R 120-150 mesh (or equivalent) Carrier gas: Nitrogen Flow rate: 80 ml/min Detector type: FID Temperatures - injection port: 250o - column: 150o isothermal
Quantify the methanol, ethanol and isopropanol present in the sample by comparing the peak areas with the corresponding peaks obtained by chromatographing the headspace produced by substituting in the procedure 1 ml of Standard alcohol solution for 1 ml of Sample solution. |