How to Measure Vitamin C Content of Citrus Fruits

By Lori Lapierre

Vitamin C, also known as ascorbic acid, is an important and powerful antioxidant. Many parts of the human body, such as the immune system, require it to function properly. The RDA (Recommended Daily Allowance) for adults is no less than 60 milligrams a day.


Citrus fruits contain the most Vitamin C among fruits and vegetables. Most purchased citrus juices or canned fruits are labeled with the amount of Vitamin C per serving. However, there are two easy methods to measure which juices have higher contents of Vitamin C, if you want to do it yourself.

Step 1

Use a Vitamin C Test Strip for Method #1. These small papers are chemically treated to measure the amount of Vitamin C in fruit juices, and are typically used in labs. They are easy to use and can be purchased online in amounts of 50 to 100 strips per box. Follow the manufacturer's directions for how to use and dispose of them.

Step 2

Make a Vitamin C testing solution for Method #2. Measure 1 teaspoon of cornstarch into a drinking glass and add 1 to 2 tablespoons of cold water. Stir well, making a paste, and then add an additional 1/2 cup boiling water. Stir this mixture until the cornstarch dissolves.

Step 3

Pour 1 cup (75 ml) of water into a second glass and add 10 drops of the cornstarch solution, using an eyedropper. With the second eyedropper, add iodine to the mixture a drop at a time, until the solution turns dark blue or purple. The amount of iodine needed will vary; pause for a few seconds between drops to allow the iodine to mix with the solution, stopping once it has reached the indicated color.

Step 4

Remove 1/10 cup (5 ml) of the iodine and cornstarch solution. Pour this into a third glass, and add 10 drops of any citrus fruit juice. The solution will become clear, as ascorbic acid causes iodine to lose color. The clearer the solution, the stronger the concentration of Vitamin C.