i found how to prepare one on the same site where you found the project
Directions for the preparation of vitamin C Indicators
* Add 2 g of corn starch or potato starch in 200 mL of cold, distilled water. Bring the mixture to a full boil in a glass beaker.
* To 1 liter of water, add 8 mL of the starch solution and 1 mL of tincture of iodine.
* Note: The color of the starch indicator should be a royal blue. Just before doing the lab, check the indicator and dilute the concentration so that a workable number of drops of fresh orange juice (5 to 25) turn the indicator colorless.
Tincture of Iodine
* Add 2 g of Iodine to 45 mL of ethanol and dissolve.
* Dissolve this mixture in 55 mL of distilled water.
* Add 2.4 grams of KI to this mixture and dissolve.
* Stock solution : dissolve 100 mg of 2,6 dichloro-indophenol salt in 100 mL of distilled water.
* Prepare a working solution by diluting the stock solution at a 1:10 ration with distilled water.
* Note: When testing the juices of citrus fruits for vitamin C content, the blue indophenol may turn pink before turning colorless because of the presence of substances other than vitamin C.