Fructose
Definition and meaning of Fructose in chemistry.
Fructose is a simple ketonic monosaccharide found abundantly in many fruits, root vegetables, and honey. It is a structural isomer of glucose with the identical chemical formula but a different connectivity, featuring a ketone functional group rather than an aldehyde. When combined with glucose, fructose forms the common disaccharide sucrose.
In more detail
Fructose, commonly known as fruit sugar, is a six-carbon polyhydroxy ketone and the sweetest naturally occurring carbohydrate. In aqueous solution, it predominantly exists as a cyclic hemiketal, establishing an equilibrium mixture of a five-membered furanose ring and a six-membered pyranose ring, with beta-D-fructopyranose being the most stable and sweetest tautomer. Fructose is metabolized in the human body almost exclusively in the liver, where it enters the glycolysis pathway via fructokinase, bypassing the major regulatory enzyme phosphofructokinase. This metabolic routing difference means fructose can be converted to triglycerides more readily than glucose if consumed in caloric excess. Commercially, significant quantities of fructose are derived from the enzymatic processing of corn starch to produce high-fructose corn syrup, a ubiquitous sweetener in the global food and beverage industry.
Key facts
| Field | Biochemistry |
|---|---|
| Formula | C6H12O6 |
| Molar mass | 180.16 g/mol |
| State | Solid (crystalline) |
| Melting point | 103 °C (decomposes) |
Honey contains a massive proportion of free fructose, which contributes to its intense sweetness and its strong tendency to absorb atmospheric moisture.
Frequently asked questions
How does fructose differ structurally from glucose?
While both share the chemical formula C6H12O6, fructose is a ketose containing a ketone functional group at carbon 2, whereas glucose is an aldose containing an aldehyde functional group at carbon 1.
Why is fructose noticeably sweeter than glucose?
The specific stereochemistry and the pyranose ring structure of fructose interact more strongly with the sweet taste receptors on the human tongue compared to the cyclic structure of glucose.