Fructose

Fructose (/ˈfrʌktoʊs, -oʊz/), or fruit sugar, is a common monosaccharide, i.e. a simple sugar. It is classified as a reducing hexose, more specifically a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. In terms of structure, it is a C-4 epimer of glucose. A white, water-soluble solid,It is one of the three dietary monosaccharides, along with glucose and galactose. Fructose is found in honey, tree and vine fruits, flowers, berries, and most root vegetables.

Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847. The name "fructose" was coined in 1857 by the English chemist William Allen Miller. Pure, dry fructose is a sweet, white, odorless, crystalline solid, and is the most water-soluble of all the sugars.

The word "fructose" was coined in 1857 from the Latin for fructus (fruit) and the generic chemical suffix for sugars, -ose. It is also called fruit sugar and levulose or laevulose, due to its ability to rotate plane polarised light in a laevorotary fashion (anti-clockwise/to the left) when a beam is shone through it in solution. Likewise, dextrose (an isomer of glucose) is given its name due to its ability to rotate plane polarised light in a dextrorotary fashion (clockwise/to the right).

Fructose adopts both cyclic six- and five-membered structure, The six membered ring can exist as either the β-d-fructopyranose and α-d-fructopyranose. The five-membered rings exists as either of two isomers β-d-fructofuranose and α-d-fructofuranose. Additionally, an acyclic (open-chain) form exists: keto-d-fructose. At 70% and 22% respectively, fructopyranose and fructofuranose are the dominant species in aqueous solution.

Fructose may be anaerobically fermented by yeast and bacteria. Yeast enzymes convert sugar (sucrose, glucose, and fructose, but not lactose) to ethanol and carbon dioxide. Some of the carbon dioxide produced during fermentation will remain dissolved in water, where it will reach equilibrium with carbonic acid. The dissolved carbon dioxide and carbonic acid produce the carbonation in some fermented beverages, such as champagne.

Fructose undergoes the Maillard reaction, non-enzymatic browning, with amino acids. Because fructose exists to a greater extent in the open-chain form than does glucose, the initial stages of the Maillard reaction occur more rapidly than with glucose. Therefore, fructose has potential to contribute to changes in food palatability, as well as other nutritional effects, such as excessive browning, volume and tenderness reduction during cake preparation, and formation of mutagenic compounds.

Fructose can be dehydrated to give hydroxymethylfurfural ("HMF", C
₆H
₆O
₃), which can be processed into liquid dimethylfuran (C
₆H
₈O). This conversion has long been proposed, not implemented, as a route to green fuels.

The primary reason that fructose is used commercially in foods and beverages, besides its low cost, is its high relative sweetness. It is the sweetest of all naturally occurring carbohydrates. The relative sweetness of fructose has been reported in the range of 1.2–1.8 times that of sucrose. However, it is the 6-membered ring form of fructose that is sweeter; the 5-membered ring form tastes about the same as usual table sugar. Warming fructose leads to formation of the 5-membered ring form. Therefore, the relative sweetness decreases with increasing temperature. However, it has been observed that the absolute sweetness of fructose is identical at 5 °C as 50 °C and thus the relative sweetness to sucrose is not due to anomeric distribution but a decrease in the absolute sweetness of sucrose at higher temperatures.