Fructose Structure: Definitions, Examples, Physical and Chemical Properties, Uses, Characteristics, Reactions, and Sources

Fructose Structure Overview

The simple ketonic monosaccharide fructose, usually referred to as fruit sugar, is found in a wide variety of plants. It frequently forms the disaccharide sucrose in plants by bonding with glucose. During digestion, it enters straight into the circulation. In the year 1847, a French scientist by the name of Augustin-Pierre Dubrunfaut made the initial discovery of fructose. Later, in 1857, an English scientist by the name of William Allen Miller formally invented the phrase.

What is Fructose?

Numerous plants, flowers, and fruits contain the straightforward ketonic monosaccharide sugar known as fructose. One of the three dietary monosaccharides—along with glucose and galactose—that are immediately absorbed into the blood after digestion is this fruit sugar. The simplest type of sugar and the fundamental component of carbohydrates are called monosaccharides. Fructose is the simplest sugar and is also the easiest sugar to digest. It is a sweet, white, flavorless, and crystalline substance in its purest form. In comparison to other sugars, it is more water-soluble. It is often found in vegetables like carrot, radish, beetroot, and sugarcane, as well as fruits like mango, litchi, cherry, and guava. It is produced commercially from sugar beets, maize, and cane.

Highlights of Fructose Structure

The following table gives the details about the fructose structure-

Properties of Fructose

The following are the properties of fructose structure-

1. 1020 °C is the temperature at which it melts.
2. Compared to other sugars, fructose absorbs moisture quickly and releases it gradually to produce hydroxymethylfurfural in the environment.
3. It is a white, crystalline substance.
4. It may undergo anaerobic fermentation using yeast or bacteria, which produces ethanol and carbon dioxide.

Uses of Fructose Structure

Here are some typical applications for fructose-

1. Energy drinks, chocolate milk, cereals, yogurt, and many other low-calorie foods employ crystalline fructose (a natural sweetener).
2. In addition, several adult medications, including liquid cough suppressants and decongestants, sweeten their products with high fructose corn syrup.
3. It contributes to improving the flavor of both pediatric food and drink.
4. Products containing HFCS (High Fructose Corn Syrup) are a blend of glucose and fructose.

Read more about the Sources of Carbohydrates.

Example of Fructose Structure

Like other simple sugars, fructose has a six-carbon linear chain containing hydroxyl and carbonyl groups that may be used to describe its structure.

History of Fructose Structure

In 1857, the Latin term Fructus (fruit) and the chemical suffix -ose, which is a general designation for sugars, were combined to form the word "fructose". Due to its propensity to spin plane polarised light in a laevorotary manner (counterclockwise/to the left) when a beam is shined through it in solution, it is also known as fruit sugar, levulose, or laevulose.

Characteristics of Fructose Structure

Fructose has a number of important properties, including being white in color when pure and dried, being odorless, tasting sweet, and having a crystalline shape. Of all the numerous kinds of sugars, it is the one that is most water-soluble. Normal sources of fructose sugar include fruits, flowers, trees, honey, berries, and root vegetables.

Chemical Properties of Fructose Structure

A polyhydroxy ketone with six carbons is fructose. Due to the durability of its hemiketal and internal hydrogen bonds, crystalline fructose adopts a cyclic six-membered structure known as -d-fructopyranose. The tautomers -d-fructopyranose, -d-fructofuranose, -d-fructopyranose, and keto-d-fructose (the non-cyclic form) coexist in equilibrium as fructose in solution. Temperature and a number of other factors, including the solvent, affect how the d-fructose tautomers are distributed in the solution. It has been determined several times that the distributions of d-fructopyranose and d-fructofuranose in water are around 70% fructopyranose and 22% fructofuranose.

Physical and Functional Fructose Structure

The following is a list of the physical characteristics of fructose molecules-

1. A molecule's freezing point is lowered by fructose molecules. As a result, it aids in lowering the rate at which water crystallizes within fruit cells.
2. About 180.16 g/mol is its molecular weight.
3. Fructose has a melting point of around 103°C.
4. The fructose sugar is sweetest between 5 and 50 °C; above that point, the sweetness decreases as the fructose's six-carbon ring transforms into a five-carbon ring. This procedure demonstrates the relevance of fructose structure.
5. The sweetest monosaccharide that we use in commercial sweeteners is this one.
6. It swiftly absorbs and holds onto the moisture for a longer time. 

Reactions to Fructose Structure

The following are some of the reactions to fructose structure-

Dehydration

Hydroxymethylfurfural, which fructose rapidly dehydrates into, may then be processed to produce liquid dimethylfuran (C₆H₁₂O₆). Future versions of this technology might function as a low-cost, carbon-neutral system for making plant-based alternatives to gasoline and diesel.

Fructose and Fermentation

Yeast or bacteria may anaerobically ferment fructose. Sugar (sucrose, glucose, or fructose, but not lactose) is converted by yeast enzymes into ethanol and carbon dioxide.[20] During fermentation, some of the carbon dioxide generated will stay dissolved in the water, where it will eventually come into balance with the carbonic acid. Some fermented drinks, like champagne, get their carbonation from dissolved carbon dioxide and carbonic acid.

Fructose and Maillard Reactions

Amino acids and fructose engage in a non-enzymatic browning process known as the Maillard reaction. The Maillard reaction's earliest phases happen more quickly with fructose than with glucose because it is more prevalent in the open-chain state. As a result, fructose has the potential to influence how food tastes as well as have other negative nutritional impacts such as excessive browning, decreased volume and softness during cake making, and the creation of mutagenic chemicals.

Food Sources of Fructose Structure

Honey, fruits, and vegetables (including sugar cane) are all natural sources of fructose. From these sources, fructose is frequently concentrated further. Foods containing white sugar (sucrose), high-fructose corn syrup, agave nectar, honey, molasses, maple syrup, fruit, and fruit juices are the highest dietary sources of fructose in comparison to other common foods and ingredients. These foods also have the highest percentages of fructose (including fructose in sucrose) per serving. Foods can include fructose, either free or linked to glucose as sucrose, a disaccharide. Foods may include fructose, glucose, and sucrose, but the amounts of each of these three sugars will vary from one item to the next.

Read more about Adulterated Food and the Variety of Food.

Interesting Facts about Fructose Structure

An intriguing fact is that nectar from flowers, which contains sucrose, is collected by bees. Then, an enzyme is used to hydrolyze, or separate, the sucrose into its glucose and fructose components.

Fructose Structure

The structure of fructose is cyclic or chair-like. The chair form of fructose is comparable to that of glucose, with a few differences in fructose's structure. Since fructose possesses a ketone functional group, the second carbon position is where the ring closure takes place. In fructose, this causes the production of an intramolecular hemiacetal or the emergence of a 5-membered ring. The carbon is in the second position, and the OH is in the fifth carbon unit. There are four carbons and one oxygen in the five-membered ring. Essentially, two configurations of CH2OH and OH groups are present, together with chiral carbon. Fructose essentially exhibits stereoisomerism.

Linear Structure

1. The Fischer projection demonstrates fructose's linear structure.
2. It displays the atoms' precise alignment while maintaining their symmetry and locations.
3. It is dextrorotatory, which is less common when the fructose molecule spins the polarized light rightward. 
4. The fructose molecule is levorotatory, which is mainly present in commercial and natural foods when it rotates the polarized light in a leftward direction.

Ring Structure

1. Haworth projections reveal fructose's ring structure.
2. The resulting pyranose ring, formed by the six-membered carbon chain, gives the molecule a crystalline structure.
3. Furanose, the most prevalent form of fructose in solutions, is a five-membered ring formed by the six-carbon molecule known as fructose.

Steps Involved in a Fructose Structure Ring Formation 

1. The hydroxyl group at the fifth carbon atom reacts intramolecularly with the ketone functional group at the second carbon atom to produce the ring.
2. The hydroxyl group's oxygen atom has a strong bonding preference for the second carbon, which houses the ketone group.
3. A hydroxyl group is created when the hydrogen atom from the hydroxyl of the fifth carbon moves to bond with the oxygen atom of the second carbon, which also contains a ketone group. 
4. Thus, between the second and fifth carbons, it creates an ether bond. 
5. Anomeric carbon is defined as having both the ether and a carbon atom that has a hydroxyl group. The group is referred to as hemiacetal.

Alpha and Beta Rings of Fructose Structure

The hydroxyl group's relocation to the second carbon causes the rings to be further categorized as alpha and beta compounds. Alpha is the name used when the hydroxyl is facing downward. It is beta when it is facing up.

Conclusion

In the commercial world, fructose, a ketohexose monosaccharide, is used as a sweetener. Due to the free carbonyl group at its second carbon, the six-carbon molecule acts as a reducing sugar. Levo-fructose predominates as its primary form. Since fructose is an isomer of glucose, its structure is more comparable to that of glucose. Fructose possesses a functional group called a ketose at its second carbon, except for that. It also varies from aldohexose to glucose, by occasionally creating a five-membered furanose ring. Honey, berries, and vine fruits all contain fructose in their natural forms.