Cooking may cause vitamin C to break down, which means heated samples could contain less of this nutrient than raw ones. You blend raw tomatoes and cherries with water, split each into two portions, and heat one of each on a hot plate while the other stays raw. An iodine-starch solution that turns dark purple measures what remains — as drops of each fruit sample cause the color to fade, more fading means more vitamin C is present. Comparing raw and cooked samples reveals whether heat reduced the amount.

An iodine-starch solution turns dark purple, and when fruit juice is added, that purple color begins to fade. The more it fades, the more vitamin C is present in the sample. By comparing how much the raw and cooked versions of tomatoes and cherries change the indicator's color, you can see directly whether heating destroys the vitamin C or concentrates it.

When tomatoes and cherries are cooked, the heat changes how much ascorbic acid remains in the fruit. To see exactly how much, you prepare an iodine-starch solution that turns dark purple. Adding drops of a blended fruit sample causes that purple color to fade — the more it fades, the more vitamin C is present. You blend each fruit with water, split it into two samples, and heat one on a hot plate while leaving the other raw. Comparing the color changes between cooked and raw samples reveals whether cooking destroys the vitamin C or, as some results suggest, concentrates it.