Preservatives

i. Sorbic Acid

Sorbic acid, food grade used as a food additive is permitted under the PFA rules (1955).

Purity

Weigh 1.5 g of the material, previously dried in a vacuum desiccator over concentrated sulphuric acid for 24 h. Dissolve in about 25 ml of ethanol, titrate with 1N NaOH using phenolphthalein as indicator. 1 ml of 1N NaOH = 0.1121 g of sorbic acid.

Aldehydes

Prepare a saturated aqueous solution of the material. In a test tube to 1 ml of this solution add 0.5 ml of Schiff’s reagent (aqueous solution of 0.125 g of crystalline rose aniline chlorohydrate in 1000 ml and decolourized with sulphuric acid) allow to stand for 10 min. Compare the colour with that produced by 1 ml of formaldehyde solution corresponding to 0.1 % aldehydes, with the same amount of Schiff’s reagent under the same conditions. The colour produced in the test solution shall not be more intense than that in the formaldehyde solution.

Test for Stability

Place 10 g of the material in a test tube and heat in an oil bath at 105°C for 90 min. The test tube should be immersed in the oil bath so that the upper level of the material is 2 cm below the surface of the oil. The material shall be taken as having passed the test if no discolouration occurs.

ii. Sodium Propionate

Sodium propionate is an anti-roping agent and a mould inhibitor. It is permitted for bread and certain foods under the PFA rules.

Purity

Weigh accurately about 250 mg of the sample and dissolve it in 40 ml of glacial acetic acid, warming if necessary to effect solution. Cool to room temperature;add 2 drops of methylrosaniline chloride (dissolve 100 mg of methylrosaniline chloride in 10 ml glacial acetic acid). Titrate with perchloric acid. Perform blank and make necessary correction. Each ml of 0.1N perchloric acid is equivalent to 9.606 mg of C3H5NaO2.

iii. Calcium Propionate

Sodium propionate is an anti-roping agent and a mould inhibitor. It is permitted for bread and certain foods under the PFA rules.

Purity

Dissolve about 400 mg of the sample, accurately weighed, in 150 ml of water, add 15 ml of sodium hydroxide and 300 mg of hydroxynaphthol blue indicator.Titrate with disodium ethylenediamine tetraacetate (EDTA) until the solution is clear blue in colour. Each ml of 0.05M Na2 EDTA (16.81 g/L) is equivalent to 9.311 mg of C6H10O4Ca.

iv. Sulphur Dioxide

Use of sulphur dioxide, food grade is permitted in certain foods under the PFA rules

Purity

An accurately measured volume of the gas shall be absorbed in alkaline solution and determined by iodometric titration.

Non-Volatile Residue

Collected 300 ml of liquid sulphur dioxide in a 500 ml Erlenmeyer flask and stopper the flask lightly with a cotton plug. Evaporate under a well-ventilated hood. When evaporation shall be complete, only a trace of residue shall be observed in the flask.

v. Silver Leaf

Silver leaf is used extensively in India for edible purposes and as a coating on sweets, pan and other eatables. Very high purity of silver has been recommended in order to avoid possibilities of contamination due to harmful elements.

Purity as per IS:2113-2002

Weigh 1 g of sample accurately into 250 ml beaker. Add 15 ml of dilute nitric acid (1:1), cover the beaker with watch glass and heat gently on the hot plate till the sample is completely dissolved. Expel all the nitrous fumes. Remove the beaker from the hot plate and remove the watch glass by washing with a fine jet avoid spurting. Dilute the content to about 100 ml with distilled water. Add 20 ml of HCl to it slowly with continuous stirring avoiding any loss of AgCl while stirring. Cover the beaker with watch glass and keep the beaker on hot plate,avoiding boiling. After 1 h check with few drops of dilute HCl for the complete precipitation of silver. Keep on the hot plate at least for 2 h ) preferably over night in a dark place).

Remove the watch glass from the beaker while washing very gently with a fine jet of reagent grade water, wash down the walls of the beaker with fine jet, and filter through previously cleaned, dried and weighed sintered glass crucible using vacuum pump. Adjust the rate of filtration, by adjusting the pressure of the pump so that it is neither too fast nor too slow. Wash the precipitate 2-3 times with dilute nitric acid (3%) and then 5-6 times with distilled water.

Dry the sintered glass crucibles with silver chloride precipitate in oven at 140°C for at least 1 h. Cool the crucibles in desiccator to room temperature and weigh after 1 h. Repeat the procedure till constant weight is obtained.

Silver (as Ag), part per thousand = (A× 0.7526×1000)/B

Where,

A= mass, in g, of silver chloride, and

B=mass, in g, of the sample.