Fructose
Augustin-Pierre Dubrunfaut found fructose in 1847. He wrote about the discovery and properties of this sugar on page 174 of his work. The French chemist identified a substance that was distinct from other known sugars at the time. William Allen Miller coined the term fructose in 1857. This English chemist created a name derived from the Latin word for fruit, which is fructus. He added the chemical suffix -ose to denote it as a sugar. The new name reflected its natural presence in many plant sources. Earlier names like levulose described how the molecule rotated polarized light to the left. Dextrose received its name because it rotated light to the right. These early observations laid the groundwork for understanding the unique behavior of this simple ketonic monosaccharide.
Fructose adopts both cyclic six- and five-membered structures in aqueous solution. The six-membered ring exists as either beta-fructopyranose or alpha-fructopyranose. The five-membered rings exist as either beta-fructofuranose or alpha-fructofuranose. An acyclic open-chain form called keto-fructose also exists. At 70% concentration, fructopyranose dominates the mixture. Fructofuranose makes up about 22% of the species found in water. The 6-membered ring form tastes sweeter than the 5-membered ring form. Warming the substance leads to formation of the 5-membered ring structure. This structural shift causes relative sweetness to decrease with increasing temperature. Absolute sweetness remains identical at 5 degrees Celsius and 50 degrees Celsius despite these changes.
Commercial production relies on three main precursors: starch, sucrose, and inulin. Maize serves as a major source of starch for industrial processing. Sugar cane and sugar beets provide the sucrose needed for conversion. Starch hydrolyzes into glucose before converting to fructose via the enzyme glucose isomerase. This process creates high-fructose corn syrup. At 60 degrees Celsius, the reaction yields a 1-to-1 mixture of glucose and fructose. Inulin converts to fructose on a commercial scale from sources like chicory. About 240,000 tonnes of crystalline fructose were produced annually by recent estimates. HFCS-55 contains 55% fructose and sweetens soft drinks. HFCS-42 contains 42% fructose and sweetens processed foods and breakfast cereals. Granulated sugar remains 99.9% pure sucrose with an equal ratio of fructose to glucose.
The liver converts most fructose and galactose into glucose for distribution in the bloodstream. Fructokinase phosphorylates fructose to form fructose 1-phosphate within the organ. Aldolase B splits this compound to produce dihydroxyacetone phosphate and glyceraldehyde. A third enzyme called triokinase phosphorylates glyceraldehyde to create glyceraldehyde 3-phosphate. These intermediates enter the gluconeogenic pathway for glucose or glycogen synthesis. Increased concentrations of these molecules drive the body toward fatty acid and triglyceride formation. Once liver glycogen is replenished, metabolic intermediates direct primarily toward triglyceride synthesis. Accumulated citrate moves from mitochondria into the cytosol of hepatocytes. Citrate lyase converts it to acetyl CoA for fatty acid synthesis. Very-low-density lipoproteins carry these triglycerides to peripheral tissues for storage in fat and muscle cells.
Fructose absorption occurs via facilitated transport involving GLUT5 transport proteins on the mucosal membrane. The concentration gradient allows flow down into enterocytes assisted by these specific proteins. Absorption capacity ranges from less than 5 grams to 50 grams per individual serving. Studies show the greatest rate occurs when glucose and fructose are administered in equal quantities. Unabsorbed fructose reaches the large intestine where colonic flora ferments it. Hydrogen produced during fermentation dissolves into blood of the portal vein. This hydrogen travels to lungs where exchange makes it measurable by breath tests. Colonic bacteria also produce carbon dioxide, short-chain fatty acids, and organic acids. Gases and acids cause symptoms like bloating, diarrhea, flatulence, and gastrointestinal pain. Exercise immediately after consumption decreases transit time and empties more fructose into the large intestine.
The European Food Safety Authority stated in 2022 that research evidence links fructose to increased risk of several chronic diseases. Moderate risk exists for obesity and dyslipidemia exceeding 50%. Low risk applies to non-alcoholic fatty liver disease, type 2 diabetes ranging from 15% to 50%, and hypertension. Excessive sugar consumption contributes to insulin resistance and elevated LDL cholesterol levels. High intakes may lead to metabolic complications such as increased visceral adiposity. The UK Scientific Advisory Committee on Nutrition disputed claims in 2015 regarding adverse health outcomes at normal diet levels. Fructose has a glycemic index of 23 compared with 100 for glucose and 60 for sucrose. It is 73% sweeter than sucrose at room temperature allowing diabetics to use less per serving. Clinical research did not support a positive relationship between dietary sugars and chronic metabolic diseases when exchanged isocalorically with other macronutrients.
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Common questions
Who discovered fructose and when was it found?
Augustin-Pierre Dubrunfaut found fructose in 1847. He wrote about the discovery and properties of this sugar on page 174 of his work.
When did William Allen Miller coin the term fructose?
William Allen Miller coined the term fructose in 1857. This English chemist created a name derived from the Latin word for fruit, which is fructus.
What are the main precursors used for commercial production of fructose?
Commercial production relies on three main precursors: starch, sucrose, and inulin. Maize serves as a major source of starch for industrial processing while sugar cane and sugar beets provide the sucrose needed for conversion.
How does the liver process fructose into glucose?
The liver converts most fructose and galactose into glucose for distribution in the bloodstream. Fructokinase phosphorylates fructose to form fructose 1-phosphate within the organ before Aldolase B splits this compound.
Why does warming fructose decrease its relative sweetness?
Warming the substance leads to formation of the 5-membered ring structure. This structural shift causes relative sweetness to decrease with increasing temperature even though absolute sweetness remains identical at 5 degrees Celsius and 50 degrees Celsius.