Fructose


from Wikipedia, the free encyclopedia
Structural formula
Structure of D- and L-fructose
D- fructose (left) L- fructose (right)

Fischer projection , open-chain representation

General
Surname Fructose
other names
  • D - (-) - fructose
  • Fructose
  • Levulosis
  • Laevulose
  • L , D , D -ketohexose
  • α-acrose
  • D -arabino-Hex-2-ulose
Molecular formula C 6 H 12 O 6
Brief description

colorless and odorless, very sweet-tasting prisms or needles

External identifiers / databases
CAS number
  • 57-48-7 [ D - (-) - fructose]
  • 7776-48-9 [ L - (+) - fructose]
  • 6035-50-3 [ DL - (±) -Fructose ( racemate )]
EC number 200-333-3
ECHA InfoCard 100,000,303
PubChem 5984
Wikidata Q122043
Drug information
ATC code

V06 DC02

properties
Molar mass 180.16 g mol −1
Physical state

firmly

density

1.59 g cm −3 (20 ° C)

Melting point
  • 106 ° C (decomposition; D- fructose)
  • 129–130 ° C ( D, L- fructose)
solubility
safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Fructose (often also fructose , from the Latin fructus "fruit", outdated levulose , colloquially fruit sugar ) is a naturally occurring chemical compound . As a monosaccharide ( simple sugar ), fructose is a carbohydrate . It occurs in several isomeric ( anomeric ) forms. In this article, the information on physiology concerns D- fructose only. L- fructose is practically meaningless.

history

The name fructose was mentioned by William Allen Miller in 1857 as an allusion to the Latin fructus 'fruit' and -ose as a suffix for carbohydrates .

properties

Fructose is a colorless, odorless, easily water-soluble, very sweet-tasting compound that forms prismatic or needle-shaped, highly hygroscopic crystals. At 60% humidity , it absorbs 0.28% water within an hour and 0.6% within 9 days. The monosaccharide is optically active and occurs in two mirror-image isomers , the so-called enantiomers . Because of its six carbon atoms, fructose belongs to the group of hexoses and because of the keto group to the ketoses ( ketohexoses ). In crystalline form it is available as a six-membered ring ( fructo pyranose ), partially dissolved as a five-membered ring ( fructo furanose ). Fructose has a calorific value of 3.75 kilocalories per gram. Fructose is a reducing sugar . It therefore tends to react with amino groups ( glycation ). The glass transition temperature of fructose is 5 ° C and the Gordon-Taylor constant (an experimentally determined constant for predicting the glass transition temperature at different mass fractions of a mixture of two substances) is 3.8.

The α and β anomers of the respective ring forms can be converted into one another in aqueous solution and are in equilibrium with one another. At 20 ° C, D- fructose dissolved in water is 76% in the β-pyranose form, 4% in the α-furanose form and 20% in the β-furanose form.

Mutarotation of fructose
D -Fructose - spellings
Wedge formula Haworth notation
D-fructose wedge line Alpha-D-fructofuranose.svg
α- D- fructofuranose
Beta-D-fructofuranose.svg
β- D- fructofuranose
Alpha-D-Fructopyranose.svg
α- D- fructopyranose
Beta-D-fructopyranose.svg
β- D- fructopyranose

Occurrence

Fructose as a simple sugar occurs naturally in pome fruit (in apples and pears each about 6 g / 100 g), berries (for example grapes at 7.5 g / 100 g) as well as in exotic fruits ( pomegranate and persimmon ) and in Honey (35.9–42.1 g / 100 g) and in synthetic honey . Table sugar ( sucrose , also cane sugar , if made from sugar cane , or beet sugar, if made from sugar beet ) is a double sugar , which is composed of one molecule each of glucose (grape sugar) and fructose. A significant portion of the sugar intake comes from industrially manufactured foods that contain fructose-glucose syrup ( high-fructose corn syrup , HFCS ).

Fructose content in different plants (in g / 100g)
food Total
carbohydrates including fiber
Total sugar Fructose glucose Sucrose Fructose /
glucose
ratio
Sucrose
in% of
total sugar
fruit              
Apple 13.8 10.4 5.9 2.4 2.1 2.0 19.9
apricot 11.1 9.2 0.9 2.4 5.9 0.7 63.5
banana 22.8 12.2 4.9 5.0 2.4 1.0 20.0
Fig , dried 63.9 47.9 22.9 24.8 0.9 0.93 0.15
Grapes 18.1 15.5 8.1 7.2 0.2 1.1 1
orange 12.5 8.5 2.25 2.0 4.3 1.1 50.4
peach 9.5 8.4 1.5 2.0 4.8 0.9 56.7
pear 15.5 9.8 6.2 2.8 0.8 2.1 8.0
pineapple 13.1 9.9 2.1 1.7 6.0 1.1 60.8
plum 11.4 9.9 3.1 5.1 1.6 0.66 16.2
vegetables              
Beetroot 9.6 6.8 0.1 0.1 6.5 1.0 96.2
carrot 9.6 4.7 0.6 0.6 3.6 1.0 77
paprika 6.0 4.2 2.3 1.9 0.0 1.2 0.0
onion 7.6 5.0 2.0 2.3 0.7 0.9 14.3
sweet potato 20.1 4.2 0.7 1.0 2.5 0.9 60.3
yam 27.9 0.5 traces traces traces - traces
Sugar cane 13-18 0.2-1.0 0.2-1.0 11-16 1.0 high
sugar beet 17-18 0.1-0.5 0.1-0.5 16-17 1.0 high
Grain              
Corn 19.0 6.2 1.9 3.4 0.9 0.61 15.0

Industrial production

Fructose is obtained industrially from vegetable starches such as corn starch . By adding the enzyme amylase , dissolved corn starch is first made into corn syrup and in a further reaction by adding glucose isomerase , high-fructose corn syrup (HFCS) is produced, e.g. B. HFCS-42 (with 42% fructose and 53% glucose in the dry matter) and HFCS-55 (with 55% fructose and 41% glucose in the dry matter, second generation HFCS from 1976). The enzymes have been immobilized since about 1972 , which kept the cost of producing HFCS in the US below the cost of importing sucrose. At the same time, this was also the first large-scale application of the immobilization of enzymes and it represents the largest technical use of immobilized enzymes in the world in terms of quantity. In addition, HFCS-90 with 90% fructose is produced by chromatography , which is used to produce HFCS-55 by dilution with HFCS -42 is used. Most soft drinks in the United States use HFCS-55 while most other HFCS-sweetened foods use HFCS-42.

In the USA, corn (more precisely: corn syrup) is used almost exclusively as a source of glucose for the production of isoglucose , which is a mixture of glucose and fructose, since fructose has a higher sweetening power with the same physiological calorific value of 374 kilocalories per 100 g. The annual worldwide production of isoglucose is eight million tons (as of 2011). Glucose syrup is used to make HFCS with the help of immobilized glucose isomerase. The glucose isomerase (more precisely xylose isomerase ) used here comes from Bacillus coagulans , Streptomyces rubiginosus or Streptomyces phaeochromogenes . The reaction is carried out at a pH of 7.5-8.2 and a temperature of 55-60 ° C. The glucose syrup produced from starch is used to produce fructose after calcium ions have been removed , since calcium ions are cofactors of amylase in the enzymatic production of glucose syrup, but inhibitors of xylose isomerase in the subsequent conversion to fructose - magnesium ions are the cofactors. Invert sugar is produced to a lesser extent than a mixture of glucose and fructose by hydrolysis of sucrose.

Industrial use

Fructose in crystalline form
Sweetening power of various sugars

For economic and logistical reasons, v. a. Due to cheap transport options in tank trucks and a 20% higher sweetening power than normal sugar (crystal / table / table sugar or sucrose ) , an increasing displacement of other compounds used for sweetening by fructose can be observed.

Use for sweetening

For a long time - until the early 2000s - fructose was recommended as a sweetener in diet foods. In relation to retail sugar, a 10 percent has D -Fructoselösung a sweetening power of 114 percent. The figures vary between 1.14 (dissolved form) and 1.8 (crystalline form). The sweetening power of fructose works synergistically with other compounds used in sweetening. The pyranose form of fructose is sweeter than sucrose, while the furanose form is about equally sweet. In the crystalline state, only the sweeter pyranose form of fructose is present. Heating fructose solutions favors the furanose form. When heated, the pyranose form is converted into the furanose form, which is why HFCS is used as a sweetener in beverages, especially in cold drinks and not in hot drinks . Fructose is more hygroscopic than other sugars and has a higher solubility in water. Therefore, sugar mixtures with fructose are softer than other sugar mixtures, which results in a more pleasant mouthfeel . However, in comparison to other sugar mixtures, due to the comparatively lower molar mass, it leads to a greater depression of the freezing point per gram used, which can be undesirable for frozen foods because they become softer.

In the United States, the commercial use of fructose increased dramatically in the 1970s - the consumption of high fructose corn syrup (HFCS), a particularly high- fructose version of corn syrup , rose from 0.23 kg per person in 1970 to 28.4 kg per person in 1997. In the USA, HFCS is mainly used in soft drinks , with the fructose content being increased to up to 55% (HFCS-55). This sweetener is particularly cost-effective for the manufacturer, since corn production is subsidized in the USA, whereas sugar imports have to be cleared. This significant change in the composition of added sugars in foods was made without first having fully studied its potential effects on human metabolism.

The Federal Institute for Risk Assessment , however (BfR) came in the evaluation of existing studies concluded that the use of fructose as a sugar substitute in diabetic foods is not useful, because an increased fructose intake impacting adversely on the metabolism and the development of obesity and the metabolic Syndrome . In addition, the increased intake of fructose can increase the risk of high blood pressure .

The quotas for fructose production regulated in the EU regulation expired on September 30, 2017. Until then, fructose had the following meaning in glucose-fructose or fructose-glucose syrup in Germany:

  • Glucose-fructose syrup
    • 8–30% fructose predominantly used
    • 42% fructose hardly used
  • Fructose-glucose syrup
    • 55% fructose no production and use
    • 90% fructose no production and use

It is to be expected that fructose production will increase (more than tripled) with the elimination of the sugar quota.

biochemistry

admission

Conversion of fructose into glycogen

In the small intestine , fructose is absorbed to varying degrees, especially more slowly than glucose . This is due to the passive transport of fructose by special proteins. on the one hand through the so-called GLUT5 (fructose transporter, apical, i.e. on the cell surface facing the intestinal lumen ), which grants the fructose access to the intestinal cells ( enterocytes ), and on the other hand through GLUT2 (fructose and glucose transporter, basolateral , ie facing the bloodstream), which allows fructose to enter the blood from the intestinal cells. In addition, GLUT5 and GLUT2 are also produced by kidney cells, which means that these cells can also absorb fructose. The Michaelis-Menten constant for the uptake of fructose is about 6 mM for GLUT5 and about 11 mM for GLUT2.

Glucose and galactose, on the other hand, are pumped into the cell with secondary activity ( SGLT1 , apical), i.e. with energy consumption. This is done in a regulated manner via a feedback inhibition. In contrast, fructose flows in an unregulated manner along its concentration gradient without any expenditure of energy . As a result, fructose is never completely absorbed from food. Especially with small children there is therefore the risk of osmotic diarrhea occurring if the amount of fructose in the diet is too high . In addition to fructose, the only monosaccharides that are absorbed directly into the bloodstream are glucose and galactose. Low doses of fructose below 1 g / kg body weight are completely absorbed in the small intestine and metabolized there. After ingesting large amounts of fructose, the concentration in the blood hardly increases because the fructose is completely absorbed by the liver. Without physical activity, fructose is converted into glucose and fatty acids . The glucose is stored in glycogen , converted into fatty acids, and then into fats, and also released into the bloodstream to help maintain blood sugar levels .

D -Fructose is in Fructolyse in cells of the liver by the enzyme Ketohexokinase C in D - 1-phosphate fructose converted - so they can not leave the cell more. Other cell types have GLUT1 , GLUT3 and GLUT4 as possible transporters , which have only a low affinity for fructose - just like the hexokinase in these cells. The supply of energy-rich phosphates is consumed by the ketohexokinase: ATPADPAMP and the AMP deaminase upregulated. It falls IMP at that over the Purinabbau the concentration of uric acid can increase. Fructose binds human to the receptor for sweet taste in the mouth, the activation of which generally positive mood changes ( emotions associated). High doses of fructose delay the onset of satiety. Fructose is the weight training taken with glucose to a faster recovery of blood glucose levels through the formation of lactate to achieve.

biosynthesis

Polyol route from glucose (1) via sorbitol (2) to fructose (3)
A = aldose reductase , B = sorbitol dehydrogenase

In body cells (with the exception of the liver - there this metabolic pathway is missing), fructose is produced from glucose via the polyol pathway, in which glucose is first reduced to sorbitol by aldose reductase ; the cosubstrate NADPH is oxidized to NADP + . Sorbitol dehydrogenase then oxidizes sorbitol to fructose, reducing the cosubstrate NAD + to NADH . The resulting loss of NADPH, in addition to the increased protein glycation, is responsible for part of the long-term consequences of a chronically increased blood sugar level (e.g. in diabetes mellitus ), since NADPH also acts as a cosubstrate of glutathione reductase from the cell to detoxify dangerous oxidation products reactive oxygen compounds is required. When the blood glucose level is increased, more glucose is converted to fructose via the polyol route with increased NADPH consumption. Due to the oversupply of glucose, the aldose reductase for its actual detoxification task is increasingly being lost. In addition, fructose and sorbitol accumulate in the cells, which on the one hand damages them osmotically, on the other hand, essential enzymes can be inhibited by high concentrations of these two sugars.

Dismantling

Conversion of fructose into triacylglycerides

Fructose is phosphorylated by fructokinase and is then metabolized as fructose-1-phosphate in glycolysis. Fructolysis is activated by insulin and inhibited by cAMP . Fructose-1-phosphate is split into glyceraldehyde and dihydroxyacetone phosphate by aldolase B. The glyceraldehyde is phosphorylated to glyceraldehyde-3-phosphate by the triokinase . Dihydroxyacetone phosphate and glyceraldehyde-3-phosphate can be used both in other breakdown pathways such as the citric acid cycle and to build up glucose via gluconeogenesis . Fructose-6-phosphate formed with the help of hexokinase is also converted into glucose-6-phosphate via a reversible reaction with glucose-6-phosphate isomerase or with L-glutamine-D-fructose-6-phosphate transamidase for the formation of Hexosamines used. The outflow of the decay products into the triacylglyceride synthesis is more significant . Triacylglycerides are deposited as depot fat , but also as fat droplets between the myofibrils of the muscles . In adipose tissue, fructose can also enter glycolysis as fructose-6-phosphate when the glycogen reserves are exhausted. Furthermore, fructose activates the Carbohydrate Response Element Binding Protein (ChREBP), which in turn induces enzymes for lipogenesis (fat formation) and gluconeogenesis .

Pathobiochemistry

Genetic defects

In humans, disorders of fructose uptake in the intestine or fructose metabolism in the liver lead to disease symptoms. Various genetic defects in fructose metabolism have been described: benign fructosuria due to a fructokinase deficiency , hereditary fructose intolerance and fructose-1,6-bisphosphatase deficiency . The frequent fructose malabsorption (also called intestinal fructose intolerance ), in which a disturbed fructose transport through the intestinal cells is assumed, and the rare but serious symptoms, hereditary fructose intolerance ( HFI ), which is caused by a hereditary disturbance of the fructose metabolism in the Is caused by the liver and in which fructose cannot be broken down or not broken down in sufficient quantities. In hereditary fructose intolerance, aldolase A is formed in the liver instead of aldolase B, which converts fructose more slowly. The accumulation of fructose-6-phosphate and fructose-1,6-bisphosphate inhibits fructose-1,6-bisphosphatase and aldolase A, thereby inhibiting glycolysis and gluconeogenesis. Therefore, with hereditary fructose intolerance, hypoglycaemia follows the consumption of fructose-containing food.

In benign fructosuria (1: 130,000, autosomal recessive ) there is a fructokinase deficiency. Fructose is increasingly excreted with the urine.

An estimated 30–40% of Central Europeans have fructose malabsorption, with around half showing symptoms. The disorder occurs mainly in childhood. Unabsorbed fruit sugar is mainly anaerobically broken down by the bacteria of the intestinal flora into carbon dioxide , hydrogen and short-chain fatty acids . These cause irritable bowel symptoms such as flatulence, abdominal pain, mushy, sometimes foul-smelling stool and diarrhea. Hereditary fructose intolerance is much rarer; There is one person affected by HFI for every 130,000 healthy people. This form of fructose intolerance causes dangerous low blood sugar levels ( hypoglycaemia ) by disrupting the glucose metabolism .

Metabolic syndrome with excessive consumption

Excessive intake of calories in the form of fructose leads to metabolic syndrome , obesity and sometimes also to type II diabetes mellitus , but not consuming fructose within a normal caloric intake. Furthermore, excessive consumption of fructose can lead to non-alcoholic fatty liver hepatitis . The body converts fructose into body fat faster than glucose. Moreover, the use of fructose appears to lower satiety to lead, as they no insulin induced -Ausschüttung and insulin also one of the satiety hormones. The increase in fructose consumption has been linked to the increase in metabolic syndrome, a risk factor for coronary artery disease .

Small amounts of fructose improve glucose tolerance and glycemic response in healthy people as well as in patients with type 2 diabetes mellitus without increased insulin secretion. There is currently insufficient data (as of 2017) to clearly associate fructose consumption with an increase in type II diabetes mellitus in humans. Compared to glucose or sucrose, fructose leads to a lower increase in insulin and triglyceride levels in the blood.

Fatty liver

Excessive consumption of beverages containing fructose, such as lemonades and other sweetened soft drinks, can damage the liver up to and including fatty liver (steatosis hepatis) with an associated pathological increase in connective tissue ( fibrosis ). The rapid increase in fructose consumption in recent years therefore not only plays an important role in the development of the metabolic syndrome, but also represents, according to studies from 2008, an independent risk factor for non- alcoholic fatty liver disease .

gout

Excessive consumption of fructose is associated with an increased risk of gout (uricopathy). Due to the increased synthesis of ATP, AMP is also increasingly broken down into uric acid , which is not very soluble and can lead to gout if it crystallizes in the joints. High-fructose fruits and fruit juices also seem to increase the risk of developing gout, while diet sodas pose no risk in this regard.

Legal position

Section 12 of the regulation on dietetic foods (so-called diet regulation) once regulated the composition of special products for diabetics. This article has been deleted since October 1, 2010, as the state of research on diabetic diets and sugar substitutes shows that these patients do not need such products and that increased fructose consumption can even have harmful effects on health (see text). Fructose is the legally protected name of a type of sugar .

The EU carried out an assessment of the effects of fructose consumption. The Scientific Advisory Committee on Nutrition in the UK found in 2015 that the effects of fructose are also caused by other sugars.

Analytics

Chromatographic Process

In complex test material, after sufficient sample preparation , fructose can be reliably detected qualitatively and quantitatively by coupling HPLC or gas chromatography with mass spectrometry . Fructose in carbonated beverages can be separated and detected by HPLC.

Fehling's trial

As an α-hydroxyketone, fructose has a reducing effect ; in addition, it can be converted into mannose and glucose in the course of the Fehling reaction in an alkaline environment (see ketol-enediol tautomerism ), so that there is an equilibrium between all these isomers .

Selivanov rehearsal

The Selivanov reaction is evidence of ketohexoses in the furanose ring form. Since it takes place in an acidic environment, there is no ketol-enediol tautomerism . The sample therefore turns out negative with glucose.

First, the fructose is heated with hydrochloric acid . This creates 5-hydroxymethylfurfural . This then reacts with resorcinol to form a red precipitate.

Selivanov reaction

literature

Web links

Wiktionary: Fructose  - explanations of meanings, word origins, synonyms, translations
Commons : Fructose  - Collection of pictures, videos and audio files

Individual evidence

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