Fructose formed in cane sugar reacts with resorcinol in the presence of hydrochloric acid to give red color.
- Dissolve 1.0 g of resorcinol in 100 ml hydrochloric acid (1:1.5)
- 1 volume of concentrated hydrochloric acid of specific gravity 1.18 mixed with 1.5 volume of water.
Note: The resorcinol flakes should be white in color.
- Curdle a known quantity of the milk by adding a little concentrated HCl (for 25 ml of milk usually one ml of concentrated HCl is required). Let stand for about 10 minutes and filter.
- To 5 ml of the modified resorcinol – HCl reagent taken in a test tube, add 1 ml of the filtered milk serum and mix.
- Place the test tube in boiling water bath for exactly 1 min. Withdraw the tube and observe the color.
- Appearance of deep red color indicates presence of sucrose, or a ketoses sugar.
Result and Interpretation
Visual observation of development of deep red color in the milk sample indicates the presence of cane sugar.
Ref: IS 1479 (Pt I) 1960) Methods of test for Dairy Industry.
(Manual Methods of Analysis for Adulterants and Contaminants in Foods, I.C.M.R., 1990)