I did a Carbohydrate lab, I understand that when seliwanoff test turns red it me

Question

I did a Carbohydrate lab, I understand that when seliwanoff test turns red it means that the tested chemical is a ketose, the test I did involved placing test tubes with the chemicals in boiling water, and then timing how long it took them to turn into a color- any color. They were sitting in the water for a good 8 minutes or longer, and none of them turned red, they just all turned yellow, which started off light and gradually became lighter. I understand that sucrose usually takes it first, and that it should eventually become red, however the lab manual instructions never had us leave the test tubes in the water until any of them turned red. So basically, how do you interpret this? We were preforming the test to find an unknown, and mine turned yellow at the same time that glucose turned yellow, would that be considered enough of an interpretation for the data do you think?

Explanation / Answer

The solution would contain both glucose and fructose. The glucose would remain yellow which is the initial colour of the seliwanoff's reagent. The fructose however being a ketose forms a furfural because of the HCL present in the seliwanoff reagent and reacts with the resorcinol to give a red cherry or pink colour.

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