Tannic acid

Description and assay

Specification history

Prepared at the 71 st JECFA (2009) and published in FAO JECFA Monographs 7 (2009), superseding specifications prepared at the 39 th JECFA (1992), published in the combined Compendium of Food Additive Specifications, FAO JECFA Monographs 1 (2005). An ADI 'not specified' was established at the 35 th JECFA (1989).

Assay

Not less than 96% on dried basis

DESCRIPTION

Amorphous powder, glistening scales or spongy mass, varying in colour from yellowish white to light brown; odourless or with a faint, characteristic odour

FUNCTIONAL USES

Clarifying agent, flavouring agent, flavour adjunct

METHOD OF ASSAY

Sample test Accurately weigh about 2.0 g of the sample (W ), transfer to a 500-ml volumetric flask, add water to dissolve and make up to the volume with water. Transfer 100 ml of this solution into a 300 ml Erlenmeyer flask and add 7.2 g of Hide Powder (a suitable grade is available from L.H. Lincoln & Son, Inc., Tanning Materials, Coudersport, Pennsylvania, 16915 USA). Shake the flask for 20 min. Let stand for 10 min. and filter through a G4-filter. The filtrate shall be clear. Pipette 50 ml of the filtrate into a tared crystallizing dish. Evaporate to dryness on a steam bath and heat in an oven at 105° for 1 h. Cool in a desiccator and weigh (a). Blank test: On each lot of Hide Powder (a suitable grade of Hide Powder may be obtained from L.H. Lincoln & Son, Inc., Tanning Materials, Coudersport, Pennsylvania, 16915 USA) a blank test has to be carried out. Weigh 7.2 g of Hide Powder EFT into a 300 ml Erlenmeyer containing 100 ml water. Proceed as directed for the Sample test, beginning with "Shake the flask for 20 min...". Cool in a desiccator and weigh (b). Calculation ⎛ (W − (a − b)) × 1000 ⎞ % Tannic Aci d = ⎜ ⎟ ⎝ W ⎠ where a is the weight of dry matter found in the sample test (g); b is the weight of dry matter found in the blank test (g); and W is weight of sample, on dry basis (g). NOTE: the multiplication factor 1000 = 10 (500 ml/50 ml) x 100 (percent).

Identification

Solubility (Vol. 4)

Soluble in water, acetone and ethyl alcohol; insoluble in ether; 1 g dissolves in about 1 ml of warm glycerine.

Colour reaction

To a 1 in 10 solution add a small quantity of ferric chloride TS. A bluish black colour or precipitate forms

Precipitate formation

A solution of the sample when added to a solution of either albumin or gelatin produces a precipitate

Test for gallic acid

Passes test after hydrolysis See description under TESTS

Test: Test for gallic acid

Proceed as directed under Chromatography (thin-layer chromatography) (see Volume 4). Sample preparation Add 20 mg of tannase to 100 ml of 1 in 1000 solution of the sample. Incubate at 37° for 2 h. Standard preparation 1 in 1000 solution of gallic acid. Developing solvent A mixture of 5 volumes of chloroform, 4 volumes of ethyl formate and 1 volume of formic acid. Spraying reagent Solution A : Prepare a 1% solution of ferric chloride (FeCl3) in 10% ethanol Solution B : Prepare a 1% solution of potassium ferricyanate (K3Fe(CN)6) in 50% ethanol Mix 1 volume of solution A and 1 volume of solution B. Adsorbent Silica gel Procedure Apply 10 μl of the sample preparation and 10 μl of the standard preparation. Stop the development when the solvent front has advanced about 15 cm, dry in air, and spray the reagent. The Rf value of the sample and that of the reference standard are identical.

Purity criteria

Loss on drying (Vol. 4)

Not more than 7% (105°, 2 h)

Sulfated ash (Vol. 4)

Not more than 1% Test 2.0 g of the sample (Method I)

Gums or dextrin

Dissolve 1 g in 5 ml of water, filter, and to the filtrate add 10 ml of ethanol; no turbidity is produced within 15 min

Resinous substances

Dissolve 1 g in 5 ml of water, filter and dilute the filtrate to 15 ml; no turbidity is produced

Condensed tannins

Not more than 0.5% See description under TESTS

Residual solvent (Vol. 4)

Not more than 25 mg/kg acetone or ethyl acetate, singly or in combination See description under TESTS

Lead (Vol. 4)

Not more than 2 mg/kg Determine using an AAS/ICP-AES technique appropriate to the specified level. The selection of sample size and method of sample preparation may be based on the principles of the method described in Volume 4 (under "General Methods, Metallic Impurities").

Test: Condensed tannins

The following HPLC method can be used for the determination of condensed tannins in the sample. Sample preparation Dissolve 200 mg of the sample in 100 ml of a mixture of 100 volumes of 10% methanol and 0.1 volume of phosphoric acid. Standard preparation Dissolve 10 mg of rutin in 100 ml of methanol. Conditions Column: Merck Hibar, LiChrosorb RP 18, 250 mm x 4.6 mm id, 5 μ (Art. 50333), or equivalent. Eluent A: 0.2% H3PO4 in water; B: 0.2% H3PO4 in methanol Gradient elution: Time (min) % A %B 0 90 10 65 25 75 66 0 100 75 0 100 76 90 10 95 90 10 Flow rate: 1 ml/min. Detection wavelength: 350 nm Injection volume: 10 μl Calculate the content of the condensed tannins as follows: A x W o % condensed tannins (as rutin) = x 100 A o x W where A is peak area of the sample (condensed tannins); Ao is peak area of the reference standard (rutin); W is weight in mg of the sample taken; and Wo is weight in mg of the reference standard taken.

Test: Residual solvents

Reagents - Acetone - Ethyl acetate Standard solutions Place 1 g of acetone and 1 g of ethyl acetate in a volumetric flask and add water to total volume of 100 ml, and prepare 0.02 - 0.4 g/100 ml solutions by dilution of this solution. Procedure Place 1 g (1.0±0.1 g) of powdered sample in a sample vial. Add 5 μl of water to the sample vial and seal it quickly with a septum. Set the sample vial in a pre-conditioned gas chromatograph and start the analysis under the below-mentioned conditions. Standard Take 1 g of tannic acid free of solvent or with known residual solvent content in a sample vial, add 5 μl of the standard solution and seal it quickly with a septum. Set the sample vial in a pre-conditioned gas chromatograph and start the analysis under the following conditions and obtain standard curves for each solvent. Determine by Gas chromatography , using a head space sampler under the following conditions: - Column: 100% methyl polysiloxane 30 m x 0.53 mm id, 1 μm film thickness - Column conditioning: Heat to 60° for 2-3 h with approximately 10 ml/min of nitrogen - Carrier gas: Nitrogen - Flow rate: 5 ml/min - Detector: Flame ionization - Temperatures - injection port: 110° - column: 40° - detector: 110° Head space sampler - Sample heating temp.: 80° - Sample heating time: 40 min - Syringe temperature: 85° - Sample gas injection: 0.4 ml Calculation ⎛ A i × f i ⎞ C i (mg/kg) = ⎜ ⎟ ⎝ W ⎠ where Ci is the concentration of solvent (mg/kg); Ai is peak are of solvent (Area units); fi is the slope of the standard curve (μg/Area units); and W is weight of sample in g.