Strictly speaking fructose is not considered a reducing sugar. But in aqueous solution, fructose and glucose can undergo spontaneous mutual transformation, and glucose is a reducing sugar. So fructose solutions can also exhibit the properties of reducing sugars.

Glucose and fructose are isomers of each other, glucose is a kind of polyhydroxy aldehyde (aldose), fructose is a kind of polyhydroxy ketone (ketose), fructose molecules do not have aldehyde, it seems to be unable to silver mirror reaction, but in fact, it is not, and the main reason is that the fructose can be in alkaline solution, two kinds of reaction: one is by the role of allyl alcoholization into aldose. The second is cleavage, resulting in organic matter containing aldehyde.

Reducing sugar test method

Ferrin reagent method

Reducing sugar and Ferrin reagent action, can generate a brick red precipitate.

Ferrin's Reagent (mainly made of NaOH solution with a mass concentration of 0.1g/mL and CuSO4 solution with a mass concentration of 0.05g/mL)

Note: Prepare it now and use it now

Plant tissues are commonly used as experimental materials, but they have to be selected. The most ideal material for this experiment is the biological tissue (or organ) with high sugar content, and the color of the tissue is light, or nearly white, such as apple and pear fruit. After the test comparison, the obviousness of the color reaction was apple, pear, white kale leaves, and white radish in order.

① Inject 2mL of the tissue solution to be tested into the test tube

② Inject 1mL of Ferrin's reagent into the test tube (liquid A and liquid B are mixed in equal quantities and then injected)

③ Put the test tube into a large beaker of 50-65 ℃ warm water and heat it up for about 2min

④ Observe the color change that occurs in the test tube