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Fructose

physical science Maturity 11-13 Next article →

Fructose is a common monosaccharide, which is a type of simple sugar. It is often called fruit sugar because it appears naturally in many plants.

Table fructose
Table fructose

This sugar is classified as a reducing hexose. Specifically, it is a ketonic simple sugar. It is one of three main dietary monosaccharides, along with glucose and galactose. Fructose is a white, water-soluble solid. It is found in honey, flowers, berries, and many vine or tree fruits. It is also present in most root vegetables. In many plants, fructose bonds to glucose to form a disaccharide called sucrose.

Sucrase
Sucrase

Chemically, fructose is quite complex because it can change its shape. In a liquid solution, it exists in several different forms. It can take the shape of a six-membered ring or a five-membered ring. The six-membered rings are called fructopyranose and α-fructopyranose. The five-membered rings are called fructofuranose and β-fructofuranose. In an aqueous solution, fructopyranose makes up 70% of the molecules. Fructofuranose makes up 22% of the molecules. There is also an acyclic form, which means an open-chain form. This specific form is called keto-fructose.

Isomeric forms of fructose
Isomeric forms of fructose

Fructose has unique physical properties that make it useful in food science. It is the sweetest of all naturally occurring carbohydrates. Its relative sweetness is between 1.2 and 1.8 times that of sucrose. The six-membered ring form is the sweetest version. As you warm the sugar, it forms more five-membered rings. This causes the relative sweetness to decrease as temperature rises. However, the absolute sweetness remains the same at 5 °C and 50 °C. This is because the sweetness of sucrose also decreases at higher temperatures.

Relativesweetness
Relativesweetness

Fructose also affects how food feels and stays fresh. It is highly water-soluble, making it difficult to crystallize from a liquid. This high solubility makes candies containing fructose softer than those using other sugars. Fructose is also a humectant. This means it absorbs moisture quickly and releases it slowly. This property helps food maintain a palatable texture and a longer shelf life. In baking, fructose increases starch viscosity very quickly. It lowers the temperature needed for starch gelatinization. This results in a higher final viscosity for the food.

DL-Fructose num
DL-Fructose num

History shows us how scientists identified this sweet molecule. Augustin-Pierre Dubrunfaut, a French chemist, discovered fructose in 1847. He documented its discovery and properties on page 174 of his work. Later, the English chemist William Allen Miller coined the name "fructose" in 1857. The name comes from the Latin word "fructus," meaning fruit. The suffix "-ose" is the generic chemical ending for sugars. Fructose is also known as levulose. This name comes from its ability to rotate plane polarized light in a laevorotary, or anti-clockwise, direction.

Isomeric forms of fructose
Isomeric forms of fructose

Industrially, fructose is produced on a very large scale. About 240,000 tonnes of crystalline fructose are produced annually. It is made from three main precursors: starch, sucrose, and inulin. Starch is often taken from maize, which is a major source. In this process, starch is hydrolyzed into glucose. Then, an enzyme called glucose isomerase converts that glucose into fructose. This creates high-fructose corn syrup. Another method involves hydrolyzing sucrose into its parts, glucose and fructose. Inulin is found in the roots of plants like chicory and can also be converted to fructose.

Sucrase
Sucrase

Fructose plays a role in various biological and chemical reactions. Yeast and bacteria can ferment fructose anaerobically. Yeast enzymes convert fructose into ethanol and carbon dioxide. The carbon dioxide can dissolve in water to create carbonic acid. This process creates the carbonation found in drinks like champagne. Fructose also participates in the Maillard reaction. This is a non-enzymatic browning process that occurs when sugar meets amino acids. Because fructose exists in an open-chain form more often than glucose, this browning happens more rapidly. This can affect the color and tenderness of baked goods.

DL-Fructose num
DL-Fructose num

Finally, understanding fructose is important for human health and nutrition. In many foods, the ratio of fructose to glucose is about 1:1. However, some fruits have different amounts. Apples and pears have more than twice as much free fructose as glucose. Conversely, apricots have less than half as much fructose as glucose. Pediatricians watch apple and pear juices closely. In children, unabsorbed fructose can cause osmotic diarrhea. This happens because the cells in the small intestine have less affinity for fructose than for glucose. This creates a high osmolarity that draws water into the gastrointestinal tract.

Fructosetransporter
Fructosetransporter
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🖼️ Images & Media (9)
File:Isomeric forms of fructose.svg
Isomeric forms of fructose.svg
File:DL-Fructose num.svg
DL-Fructose num.svg
File:Relativesweetness.svg
Relativesweetness.svg
File:Table fructose.JPG
Table fructose.JPG
File:U.s.sugarconsumption.2.svg
U.s.sugarconsumption.2.svg
File:Sucrase.svg
Sucrase.svg
File:Fructosetransporter.svg
Fructosetransporter.svg
File:Fructose-glycogen.svg
Fructose-glycogen.svg
File:Fructose-triglyceride.svg
Fructose-triglyceride.svg
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