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Sucrose
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Sucrose (common name: table sugar, also called saccharose) is a disaccharide of glucose and fructose, with the molecular formula C12H22O11.
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Encyclopedia
| Solubility of Pure Sucrose |
|---|
| Temperature(C) | g Sucrose/g Water |
|---|
50 | 2.59 |
55 | 2.73 |
60 | 2.89 |
65 | 3.06 |
70 | 3.25 |
75 | 3.46 |
80 | 3.69 |
85 | 3.94 |
90 | 4.20 |
Sucrose (common name: table sugar, also called saccharose) is a disaccharide of glucose and fructose, with the molecular formula C12H22O11. Its systematic name is a-D-glucopyranosyl- (1?2)-ß-D-fructofuranoside (ending in "oside", because it's not a reducing sugar). It is best known for its role in human nutrition and is formed by plants but not by other organisms including animals.
Physical and chemical properties
Pure sucrose is most often prepared as a fine, white, odorless, crystalline powder with a pleasing, sweet taste; the common table sugar. Sucrose is generally isolated from natural sources, however its chemical synthesis was first achieved in 1953 by Raymond Lemieux.
Like other carbohydrates, sucrose has a hydrogen to oxygen ratio of 2:1. It consists of two monosaccharides, a-glucose and fructose, joined by a glycosidic bond between carbon atom 1 of the glucose unit and carbon atom 2 of the fructose unit. What is notable about sucrose is that unlike most disaccharides, the glycosidic bond is formed between the reducing ends of both glucose and fructose, and not between the reducing end of one and the nonreducing end of the other. The effect of this inhibits further bonding to other saccharide units. Since it contains no anomeric hydroxyl groups, it is classified as a nonreducing sugar. Acidic hydrolysis can be used in laboratories to achieve the hydrolysis of sucrose into glucose and fructose.
Sucrose melts and decomposes at 186 °C to form caramel, and when combusted produces carbon, carbon dioxide, and water. Water breaks down sucrose by hydrolysis, however the process is so gradual that it could sit in solution for years with negligible change. If the enzyme sucrase is added however, the reaction will proceed rapidly.
Reacting sucrose with sulfuric acid dehydrates the sucrose and forms the element carbon, as demonstrated in the following equation:
- C12H22O11 + H2SO4 catalyst ? 12 C + 11 H2O
Commercial production and use
Sucrose is the most common food sweetener, although it has been replaced in American industrial food production by other sweeteners such as fructose syrups or combinations of functional ingredients and high intensity sweeteners. This is due to the subsidization of domestic sugar by the US government and an import tariff on foreign sugar, raising the price of sucrose to levels above those of the rest of the world. This makes HFCS more cost efficient for many sweetener applications.
Sugar is also used in the manufacturing of an amateur rocket motor propellant called rocket candy. In that propellant it is the fuel with potassium nitrate as the oxidizer.
Sucrose is the most important sugar in plants, and can be found in the phloem sap. It is generally extracted from sugar cane or sugar beet and then purified and crystallized. Other (minor) commercial sources are sweet sorghum and sugar maples.
Sucrose is ubiquitous in food preparations due to both its sweetness and its functional properties; it is important to the structure of many foods including biscuits and cookies, cakes and pies, candy canes, ice cream and sorbets, and also assists in the preservation of foods. As such it is common in many processed and so-called “junk foods.”
Sugar as a macronutrient
In mammals, sucrose is very readily digested in the stomach into its component sugars, by acidic hydrolysis. This step is performed by a glycoside hydrolase, which catalyzes the hydrolysis of sucrose to the monosaccharides glucose and fructose. Glucose and fructose are rapidly absorbed into the bloodstream in the small intestine. Undigested sucrose passing into the intestine is also broken down by sucrase or isomaltase glycoside hydrolases, which are located in the membrane of the microvilli lining the duodenum. These products are also transferred rapidly into the bloodstream.
Sucrose is digested by the enzyme invertase in bacteria and some animals.
In human nutrition
Sucrose is an easily assimilated macronutrient that provides a quick source of energy to the body, provoking a rapid rise in blood glucose upon ingestion. However, pure sucrose is not normally part of a human diet balanced for good nutrition, although it may be included sparingly to make certain foods more palatable. Large crystals are sometimes grown from aqueous solutions of sucrose on a string (or other nucleation surface) to form rock candy, a confection.
Overconsumption of sucrose has been linked with some adverse health effects. The most common is dental caries or tooth decay, in which oral bacteria convert sugars (including sucrose) from food into acids that attack tooth enamel. Sucrose, as a pure carbohydrate, has an energy content of 3.94 kilocalories per gram (or 17 kilojoules per gram). When a large amount of foods that contain a high percentage of sucrose is consumed, beneficial nutrients can be displaced from the diet, which can contribute to an increased risk for chronic disease. It has been suggested that sucrose-containing drinks may be linked to the development of obesity and insulin resistance. Although most soft drinks in the USA are now made with high fructose corn syrup, not sucrose, this makes little functional difference, since high fructose corn syrup contains fructose and glucose in a similar ratio to that produced metabolically from sucrose.
The rapidity with which sucrose raises blood glucose can cause problems for people suffering from defects in glucose metabolism, such as persons with hypoglycemia or diabetes mellitus. Sucrose can contribute to development of the metabolic syndrome. In an experiment with rats that were fed a diet one-third of which was sucrose, the sucrose first elevated blood levels of triglycerides, which induced visceral fat and ultimately resulted in insulin resistance. Another study found that rats fed sucrose-rich diets developed high triglycerides, hyperglycemia, and insulin resistance.
See also
General references
External links
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