Instead of the Biuret Reagent, the following may be used:
* Fehling’s Solutions A and B
* Sodium hydroxide and copper (II) sulphate solutions
1. Add 2 cm3 of the liquid food sample* to a clean, dry test tube 2. Add 2 cm3 of Biuret Reagent. Alternatively:
* Use sodium hydroxide solution and copper sulphate solution instead. Add 1 cm3 of sodium hydroxide solution (40% or bench solution) and 1% copper (II) sulphate solution dropwise – drop by drop - to the food sample * Use Fehling's A and B solutions instead. Fehling's A and B should be freshly prepared. Fehling’s A is copper (II) solution and Fehling's B is a mixture of sodium potassium tartrate and sodium hydroxide solution. 1cm3 of each solution – A and B – should be added to the food sample. 3. Repeat steps 1 and 2 with de-ionized water to prepare a negative controland with albumin (egg white) to prepare a postive control. 4. Shake well and allow the mixture to stand for 5 minutes. 5. Observe any color change.
* Prepare liquid samples from solid foods. Crush the solid food, add a little de-ionized water and decant the liquid. This liquid should be used for the food test. The quantity of food crushed and water used depends on the number of tests to be conducted.
Sudan stain test is often used to determine the level of fecal fat to diagnose steatorrhea. A small sample is dissolved in water or saline, glacial acetic acid is added to hydrolyze the insoluble salts of fatty acids, a few drops of alcoholic solution of Sudan III are added, the sample is spread on a microscopic slide, and heated twice to boil. Normally a stool sample should show only a few drops of red-orange stained fat under the microscope. The method is only semiquantitative, however due to its simplicity it is used for screening. Using Simple Chemical Indicators
We can test for the presence of these important compounds in food by using chemical reagents that react in...