|Molecular formula||C 12 H 22 O 11|
colorless and odorless crystalline solid with a sweet taste
|External identifiers / databases|
|Molar mass||342.30 g mol −1|
1.57 g cm −3 (30 ° C)
185–186 ° C (decomp. From approx. 160 ° C)
very easily soluble in water (4.87 g per g water at 100 ° C)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Sucrose [ zaxaroːzə ] (to Latin saccharum or ancient Greek σάκχαρον sákcharon , "sugar"), commonly known as table sugar , granulated sugar or simple sugar called, is a disaccharide and carbohydrate . Other names for sucrose are cane sugar, beet sugar, refined sugar or refined sugar, brown sugar (in the caramelized refined state), raw sugar (in the unrefined state , which is often brown, but not to be confused with it ) and sucrose or sucrose.
Sugar beet , sugar cane and sugar palm in particular contain this disaccharide in economically useful quantities. In sucrose, one molecule each of α- D - glucose and β- D - fructose are linked by an α, β-1,2- glycosidic bond .
Occurrence, extraction and importance in plants
Sucrose is formed by many plants through photosynthesis ; for the production of household sugar , sugar beet , sugar cane and sugar palm (mainly in Indonesia) are of particular importance. Sucrose is also obtained in smaller quantities from the sap of the sugar maple . In addition, the exclusively or predominantly sucrose-containing forms phloem sap of many plants the basis of the honey production - by the bees either directly vegetable exudates such as nectar or the honeydew precipitates referred to by phloem sap sucking insects (v a.. Schnabelkerfen such as aphids , scale insects , leaf fleas , Motte scale insects as well as various planthoppers ) collect.
The biosynthesis of sucrose takes place in the cytoplasm of plant cells of the hexose - intermediates UDP-glucose and fructose 6-phosphate . The two monosaccharides are formed from triose phosphates , which arise as a net gain from the carbon assimilation of photosynthesis ( Calvin cycle ) in the chloroplast . The two triose phosphates glyceraldehyde-3-phosphate and dihydroxyacetone phosphate are either used in the chloroplast for the synthesis of starch (storage starch ) or exported from the chloroplast into the cytosol , where hexoses are formed, which are used to synthesize sucrose (or other carbohydrates or amino acids).
For this purpose, fructose-1,6-bisphosphate is first formed by a condensation reaction between glyceraldehyde-3-phosphate and dihydroxyacetone phosphate , which is then converted to fructose-6-P by dephosphorylation . Glucose-6-P is also formed from fructose-6-P by isomerization , which is activated by subsequent reaction (after previous re-isomerization to glucose-1-phosphate ) with uridine triphosphate (UTP) to uridine diphosphate-glucose ( UDP-glucose ).
The subsequent condensation of UDP-glucose and fructose-6-P to sucrose-6-phosphate is catalyzed by the enzyme sucrose-phosphate synthase . The energy required for this is provided by the cleavage of uridine diphosphate (UDP). Finally, the phosphate residue is split off in an irreversible reaction by the enzyme sucrose phosphate phosphatase, so that sucrose is formed.
Importance as a transport sugar
Sucrose is the most important transport sugar in plants. It is better suited to this than free hexoses, as it is chemically inert as a non-reducing disaccharide . The sucrose produced by photosynthesis in green plant cells when exposed to light reaches the apoplasts through passive transport and then through active transport into the assimilate- conducting phloem of the plant's conducting tissue . In the phloem it becomes other, non-photosynthetic tissues, such as B. growth zones or storage tissues transported.
Dismantling and recovery
There are different possibilities for the breakdown of sucrose in the target tissues.
In growth zones such as shoot and root tips ( meristems ), sucrose from the phloem is transported symplasmically by plasmodesmata . In the cells, in reverse of the synthesis reaction, the enzyme sucrose synthase cleaves it with UDP to form UDP-glucose and fructose. The two hexoses can be converted to glucose-6-P and z. B. be introduced into glycolysis to generate energy .
In storage tissues, sucrose is transported apoplastically from the phloem to the target cells. It can be taken up by active transport into the cell and broken down there by the sucrose synthase. The majority, however, is split into glucose and fructose by invertases in the cell wall . The two monosaccharides can be taken up by the cell by symporters , where they are transported as glucose-6-P in the chloroplast and used for the synthesis of storage strength.
The sucrose heard like other sugars to the carbohydrates . It is a disaccharide (double sugar). Sucrose is formed by splitting off water from one molecule each of α- D - glucose ( pyranose form ) and β- D - fructose ( furanose form ). These two molecules are linked to one another via an α, β-1,2- glycosidic bond (glucose α1-2 fructose).
Sucrose is a non- reducing disaccharide. Non-reducing disaccharides are linked to one another via their two anomeric C atoms O -glycosidically, their chemical name ends with -sid . This means that the two components are present in the sucrose molecule in such a way that no aldehyde group can be formed with ring opening (neither from the glucose nor from the fructose molecule). These non-reducing groups of atoms are called acetals . In contrast to hemiacetals, acetals are comparatively stable in a basic and neutral environment. They can only be opened by acid catalysis, the disaccharide z. Sometimes it is split into monosaccharides , resulting in invert sugar (equal parts of glucose and fructose ). Sucrose shows almost no mutarotation due to the lack of ring opening in a neutral environment .
Heating and burning
When sucrose is heated to 185 ° C, it melts and, with decomposition, forms a brownish melt ( caramel ).
Sucrose is very soluble in water. As with most solids, the solubility is temperature-dependent:
|Temperature in ° C||ω sucrose /%||g sucrose / kg water||Density in g / cm³|
At 20 ° C a solution with 67% mass fraction ( ω ) (density 1.33 kg / l) is obtained, at 100 ° C, on the other hand, a 83% by weight saturated solution with 83% mass fraction ( ω ) (density 1, 44 kg / l), which no longer separates crystals when it cools down ("hindered crystallization"). It should also be noted that a solution with 60% mass fraction ( ω ) boils at 105 ° C, a solution with 80% mass fraction ( ω ) at 113 ° C and a solution with 90% mass fraction ( ω ) at 132 ° C. (The latter values are taken from the phase diagram of sucrose and water at 100 kPa).
Rotation of polarized light
Sucrose is chiral and therefore optically active : In an aqueous solution, sucrose turns polarized light clockwise ( specific angle of rotation α = + 66.5 ° · ml · dm −1 · g −1 ). The breakdown of sucrose creates a mixture ( invert sugar ) that consists of half glucose and half fructose . This mixture rotates polarized light counterclockwise (specific angle of rotation α = −20 ° · ml · dm −1 · g −1 ), so one observes a reversal of the direction of rotation ("inversion"); the 1: 1 mixture of fructose and glucose is therefore also known as invert sugar .
The reliable qualitative and quantitative determination of sucrose is possible after appropriate sample preparation in urine and blood plasma by coupling high-performance liquid chromatography with mass spectrometry . The coupling of gas chromatography with mass spectrometry can also be used for determination in plant material . The sugars to be determined are converted into volatile trimethylsilyl derivatives .
The sweetness is a dimensionless quantity which indicates the relative sweetness of a substance. The sweetness values refer to sucrose, which is assigned a sweetness of 1. The sweetening power is used for a semi-quantitative comparison, particularly with other natural or artificial sweeteners. Sweeteners can have a sweetening power several hundred or thousand times that of sucrose. Interestingly, a derivative of sucrose, D - (+) - sucrose octaacetate , is one of the most bitter compounds known.
Use of sugar as a food
Sucrose is traditionally used in a variety of forms as a food and food additive.
carbohydrates including fiber
|Total sugar||Fructose||glucose||Sucrose||Fructose /
|Fig , dried||63.9||47.9||22.9||24.8||0.9||0.93||0.15|
Effect of sugar consumption on the organism
Until the industrial revolution in the 19th century, pure sugar was hardly accessible to broad sections of the population in Central Europe. Sugar was mainly supplied to the body when eating vegetables and fruits as well as honey. It was only since the cultivation of sugar beet around 1800 and the beginning of the industrial refining of sucrose that the organism was confronted with larger amounts of sugar.
High sugar consumption can, especially if it is "free" sugars (English: free sugars ) is - are meant mono- and di-saccharides, which are the foods by the manufacturer, cook or consumer added and naturally in honey, syrups and fruit juices contained sugar - lead to obesity and thus to an increased risk of disease for diabetes mellitus .
Studies by John Yudkin suggest that there is a link between sugar intake and the frequency of heart attacks. It is debated whether sugar promotes the development of cancer and whether a sugar-free diet can hinder the growth of cancer. This thesis has some supporters even among doctors, is actively researched, and there are initiatives for a cancer diet based on a sugar-free or low-sugar diet.
Missing or insufficient dental care after consuming sugary foods leads to the formation of dental caries . Many types of sugar can be converted to tooth-damaging acids by bacteria in the mouth. In particular, sucrose is processed by the bacterium Streptococcus mutans into dextrans , with the help of which these can adhere particularly stubbornly to teeth.
The World Health Organization recommends that so-called free sugars should make up no more than 10% of the daily human energy intake, and ideally should be reduced to 5%. This is mostly exceeded in industrialized countries.
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