Aldose vs Ketose: Difference and Comparison

The suffix having letters o, s, and e in chemistry refers to the compound of sugar (a colourless and water-soluble compound consisting of hydrogen, oxygen, and carbon atoms).

Aldose and ketose are sugar compounds since they end with the letters (o, s, e) constitutively. Hydrolysis2 does not break down these compounds into smaller carbs molecules. This process is known as monosaccharides.

Key Takeaways

  1. Aldoses contain an aldehyde functional group, while ketoses possess a ketone group.
  2. Aldoses exhibit higher reactivity than ketoses due to the presence of the aldehyde group.
  3. Monosaccharide examples include glucose and galactose for aldoses and fructose for ketoses.

Aldose vs Ketose

An aldose is a simple sugar that contains an aldehyde functional group (-CHO) at the end of its carbon chain. An example of aldoses is glucose. A ketose is a simple sugar containing a ketone functional group (-C=O) within its carbon chain. Examples of ketoses include fructose and ribulose.

Aldose vs Ketose

Aldose monosaccharides are present in plants. The chemical formula of aldose is Cn(H2O)n. The simplest form of aldose is triose glyceraldehyde when the value of n is 3.

If the value of n is either 1 or 2, the molecule formed is not a carbohydrate. When aldose is isomerized, it becomes ketose.

Ketose monosaccharides are present in processed food. Since it consists of a single ketone group, the most straightforward chemical formula of ketose is CO(CH2OH)2.

These sugar compounds belong to the group of ketones. When ketose is isomerized, it becomes aldose. Examples of ketose are fructose, psicose, and sorbose. All have the chemical formula C6H12O6.

Comparison Table

Parameters of ComparisonAldoseKetose
Present in Aldose sugar compound is present in plants.Ketose sugar compound is present in processed food.
Consists ofAldose consists of one aldehyde group.Ketose consists of one ketone group.
Seliwanoff’s test The aldose becomes light pink when Seliwanoff’s test is performed.The ketose becomes deep cherry red on performing the Seliwanoff test.
Chemical FormulaThe chemical formula of aldose is Cn(H2O)n.The ketose becomes deep cherry red on conducting the Seliwanoff test.
FormationThe aldose will form glycolaldehyde.The ketose will form dihydroxyacetone.

What is Aldose?

Any carbohydrate (compound of carbon, hydrogen, and oxygen) compound containing the aldehyde group (RCH O) at the end of the structural formula. Since aldose has o,s, and e letters at the end, it is a sugar compound comprising the carbon chain.

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D-aldose or L-aldose sugar compounds are the two types of aldose sugar compounds. The Fischer projection designed by Emil Fischer recognizes both forms. Fischer projection is a representation of a three-dimensional molecule in two dimensions.

We are starting with the most basic aldose, glyceraldehyde, to grasp the D-aldose and L-aldose better. Look at the chemical formula to see where the hydroxide (OH) is on the chiral carbon (an asymmetric carbon bonded to multiple atoms).

If the OH group is present on the right side of the chiral carbon in the glyceraldehyde chemical formula, it is D-aldose. If the OH group is present on the left side, it is L-aldose.

Seliwanoff’s test (a biochemical test devised by a Russian scientist) determines whether a sugar molecule is an aldose or ketoSeliwanoff’s reagent (Resorcinol and hydrochloric acid) is used in this test.

Aldose sugar dehydrates at a slower rate, according to this test. Moreover, under this test, the colour of Aldose appears to be light pink.

What is Ketose?

Ketose is also a monosaccharide in which the ketone group is present. In one sugar molecule, one ketone group is present. The common form of ketose consists of three-carbon molecules, and its name is dihydroxyacetone.

Ketose sugar is digested in the body very rapidly and is the sweetest of all kinds of sugaIt’sIt’s found in prepared foods. As a result, if ingested in large quantities, it could be harmful to the human body and lead to obesity and diabetes.

Ribulose is another type of ketone sugar that is complex. However, this ketone sugar is used for the basic flavouring of the food. Xylulose is also similar to ribulose but does not consist of oxygen molecules. It is also known as a natural carbohydrate.

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A well-known ketone sugar, fructose is not only a complex sugar but is also found in most foods, especially syrups, candies, and junk food. It means we consume fructose most of the time while eating processed food.

Ketone sugar is dehydrated more rapidly (three times) Seliwanoff’s reagent is added to it to conduct the Seliwanoff test.

During this test, ketone sugar takes the colour of red cherry and is easily distinguishable from aldose sugar. Under the process of isomerization, ketone sugar becomes aldose sugar.

Main Differences Between Aldose and Ketose

  1. In Seliwanoff’s test, aldose does not become dehydrated as quickly as ketose, which becomes dehydrated three times.
  2. Aldose monosaccharides contain the aldehyde groups. On the other hand, ketose monosaccharides contain the ketone groups.
  3. When aldose reacts with the Seliwanoff reagent during the Seliwanoff test, it turns light pink. However, when ketose reacts with the reagent, it turns a cherry red.
  4. Aldose sugar is present in plants, so it is more beneficial for the human body than ketose sugar, which is present in unhealthy meals (soft drinks, candies, etc.)
  5. Aldose sugar can be converted into ketose sugar by the process of isomerization. Moreover, ketose sugar can also be converted into aldose by the same process.
References
  1. https://www.sciencedirect.com/science/article/pii/002228369090316E
  2. https://www.pnas.org/content/87/4/1362.short

Last Updated : 03 July, 2023

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9 thoughts on “Aldose vs Ketose: Difference and Comparison”

    • I agree with you, Sonia15. Knowing the differences between the two is essential in knowing the effects of sugars on the body.

      Reply
  1. It’s interesting that ketose sugars are present in processed food and have a negative impact on the body. It really does show that we are what we eat.

    Reply
  2. I have some contention with the idea that aldose sugar is more beneficial than ketose sugar. I think that’s an oversimplification of the issue.

    Reply
  3. Aldose or L-aldose sugars have a lot of interesting facets to them that I had never heard about before. Thanks for the post.

    Reply
  4. This is a great post! The information is explained thoroughly and the mention of Seliwanoff’s test really solidifies the explanation.

    Reply
    • I had never heard of Seliwanoff’s test before, so it was really interesting to learn about. It’s amazing the impact of a simple chemical test.

      Reply

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