Difference Between Aldose and Ketose

The suffix having letters o, s, e in chemistry is used to refer to the compound of sugar (a colorless 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.

Aldose vs Ketose

The main difference between aldose and ketose is that aldose consists of a single group of aldehyde (RCHO) with the chains of a carbon atom. On the other hand, ketose consists of a single ketone group per molecule. Moreover, glucose is a type of aldose, while fructose is an example of ketose.

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 simplest 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 Between Aldose and Ketose

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 that consists of the carbon chain.

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.

Starting with the most basic aldose, glyceraldehyde, to better grasp the D-aldose and L-aldose. Now, 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) is used to determine whether a sugar molecule is an aldose or ketose. Seliwanoff’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 color 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 sugars. It’s usually 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 flavoring of the food. Xylulose is also similar to ribulose but does not consist of oxygen molecules. It is also known as a natural carbohydrate.

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) when Seliwanoff’s reagent is added into it to conduct the Seliwanoff test.

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

Main Differences Between Aldose and Ketose

  1. During 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 Seliwanoff reagent during the Seliwanoff test, it turns light pink. However, when ketose reacts with the reagent, it turns a cherry red color.
  4. Aldose sugar is present in plants, so it is 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.

Conclusion

The compound of sugar ends with the suffix having spelling (o,l, and e). Sugar is made from three atoms (hydrogen, oxygen, and carbon) and, it is known as carbohydrates that provide energy to the human body. Aldose and ketose are sugar compounds, therefore, they have oxygen, hydrogen, and carbon atoms.

Aldose is the more healthy and calorie-deficient sugar compound as compared to ketose (an unhealthy form of sugar found in junk food and sugary items (soft drinks, candies, syrups). Examples of aldose sugar are glucose, galactose, and ribose. On the contrary, the examples of ketose sugar are fructose, erythrulose, and ribulose. To distinguish between both the sugars, a color-based test was designed by Russian scientist, Seliwanoff.

References

  1. https://www.sciencedirect.com/science/article/pii/002228369090316E
  2. https://www.pnas.org/content/87/4/1362.short

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