in fruits/vegetables by using the DCPIP test (2008)
Principle : Vitamin C is a strong reducing agent. It can decolorize the blue dye DCPIP. The amount of vitamin C
in a food sample
can be estimated by
the amount of it
that is used to decolorize
a fixed amount of DCPIP.
Test tube, clean and dry
Test tube rack
5 ml syringe or a good quality squeezing pipette
1 ml pipette
________% vitamin C solution, (standard for calibration) ; prepared from commercial vitamin C tablet (0.02 %) ________ % DCPIP solution, freshly prepared
Possible samples :
* grape juice, paper pack
● lemon juice, diluted from fresh squash (Citrus fruit)
● orange juice, diluted from fresh squash (Citrus fruit)
● orange juice, diluted from bottled drink Mr. Juicy (Citrus fruit) * kiwi fruit juice, diluted from fresh squash (non-citrus fruit, but high in vitamin C) ● green pepper extract / juice
1. Use a 1 ml pipette and a pipette filler to prepare a test tube with 1 ml of blue DCPIP solution. Prepare a few in a batch. 2. Fill a 5 ml syringe with the standard vitamin C solution. (Or use a dropper) 3. Slowly (gently) add the vitamin C solution into the DCPIP test tube drop by drop. [ Precautions : Hold the dropper vertically. Make sure that the drop size is constant.] 4. After adding one drop, DO NOT shake the contents.
5. Stop dropping when the blue colour disappears.
[The end point is taken when the blue solution suddenly becomes colourless.] 6. Record the number of drops of vitamin C solution required to decolourise the DCPIP solution. 7. Repeat the experiment twice (= two times).
8. Enter the results into the table below. [Each student must enter his/her data sheet.] 9. Repeat the experiment for other fruit juices.
10. Rinse the dropper/syringe with water and then a new fruit juice to reduce contamination...