SOP: Detection of Saccharin by the Resorcinol Test

GIFSQ — Global Institute for Food Safety & Quality

Principle

Saccharin is extracted from the beverage with ether after strong acidification, and the residue is identified by the resorcinol test: heating saccharin with resorcinol and sulphuric acid gives a dark-green product that turns fluorescent green on alkalinization. Saccharin is the only synthetic sweetening agent permitted in artificial carbonated beverages; no artificial sweetening agents are permitted in fruit-juice beverages.

Apparatus required

• Separating funnels
• Water bath

Reagents

a. Dilute the beverage with water (1+4).

b. Hydrochloric acid (concentrated).

c. Diethyl ether.

d. Resorcinol (50 mg per test).

e. Concentrated sulphuric acid.

f. 5 N sodium hydroxide solution.

Procedure

Dilute the beverage with water (1+4) and make strongly acidic with HCl

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Extract with diethyl ether and separate the ether layer

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Remove the solvent from the ether extract

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Test the residue: taste it — saccharin is intensely sweet — or confirm by the resorcinol test

Resorcinol test

To the residue add a few milligrams (50 mg) of resorcinol and 10 ml of H₂SO₄

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Heat gently until a dark-green colour forms

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Cool carefully, add 10 ml of water and an excess of 5 N sodium hydroxide solution — saccharin gives a fluorescent green colour

Precautions

• The sweetness test is a screening indication only; confirm with the resorcinol colour reaction.
• Heat gently — overheating chars the mixture and masks the colour change.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.