Products
Carbohydrates (“sugars”) are found in many natural and processed foods, pharmaceuticals, medical devices, and dietary supplements. For example, foods containing carbohydrates include pasta, cereals, flour, dough, bread, legumes, potatoes, corn, honey, sweets, fruits, sweet beverages, and dairy products.
Structure
Carbohydrates are natural products and biomolecules that are usually composed of only carbon (C), hydrogen (H), and oxygen (O) atoms. Other atoms may be included, for example nitrogen (N) in the amino sugars. The name is derived from carbon and water, and in fact the molecular formula of monosaccharides can be expressed as follows: Cn(H
2
O)n. For example, the following applies to glucose: C
6
H
12
O
6
= C
6
(H
2
O)
6
. Carbohydrates carry hydroxyl groups and they are aldehydes or ketones. They can be considered as oxidation products of polyhydric alcohols. Depending on the number of carbon atoms, the simple sugars ( monosaccharides) are named as follows:
- Trioses (3), e.g. glyceraldehyde.
- Tetroses (4), e.g. erythrose
- Pentoses (5), e.g. ribose, xylose
- Hexoses (6), e.g. glucose, fructose
Glyceraldehyde is a triose and the simplest aldose:
Examples: Aldose
The following figure shows examples of aldoses:
Ring formation
Carbohydrates can react intramolecularly to form stable rings. These are called hemiacetals and hemicetals. Rings with 5 members are called furanoses and with 6 members pyranoses. And a distinction is made between aldoses (aldehydes) and ketoses (ketones). For example, fructose is a ketohexose and glucose is an aldohexose.
Stereochemistry
Carbohydrates typically have multiple chiral centers and a large number of stereoisomers. The prefixes D- (dextro, right) and L- (levo, left) have become accepted for designating pairs of enantiomers. They refer to the configuration of the carbon atom furthest from the carbonyl group (C=O). In nature, the D-sugars occur frequently, but not exclusively. Two diastereoisomers are possible in ring formation. The hydroxyl group can be oriented downward (α-glucose) or upward (β-glucose). This is referred to as anomers and the anomeric C atom or center. In solution, the two ring forms and the open-chain form are present.
Multiple sugars
A bond produces the disaccharides (2), trisaccharides (3), oligosaccharides (3 to 10), and the polysaccharides, which consist of hundreds to many thousands of units, from individual simple sugars (monosaccharides). This is referred to as glycosidic bonding. In this process, sugars with the α- and β-configuration can bond to each other at the anomeric center. Starches are present in the α-configuration, whereas celluloses are present in the β-configuration, and they are therefore indigestible for humans and are excreted as calorie-free dietary fiber. A distinction is also made as to which C-atoms or hydroxy groups are linked together. Glucose typically forms 14 and 16 bonds.
Representative
The following is a small list of known representatives. Numerous other carbohydrates exist. Monosaccharides (simple sugars):
- Glucose (dextrose)
- Fructose (fruit sugar)
- Galactose (mucilage sugar)
- Mannose
- Ribose, deoxyribose (building blocks of RNA and DNA).
- Xylose
- Arabinose
Disaccharides (dual sugars, 2 units):
- Lactose (milk sugar: glucose + galactose).
- Maltose (malt sugar, glucose + glucose).
- Sucrose (table sugar: glucose + fructose).
Trisaccharides (triple sugar, 3 units):
Oligosaccharides (3 to 10 units):
- Maltodextrin (mixture of monomers, oligomers and polymers of glucose).
Polysaccharides are polymers (macromolecules) with hundreds to many thousands of carbohydrate units:
- Starches: Amylose, amylopectin (glucose polymer).
- Celluloses (glucose polymer)
- Glycogen (glucose polymer)
- Dietary fiber
Meaning
Carbohydrates are among the most important groups of substances in nature.The most common organic molecules on earth are the celluloses, which are polymers of glucose. As substrates, plants use carbon dioxide and water for synthesis and solar radiation as an energy source in photosynthesis. Carbohydrates play a central role as energy stores (e.g., starch, glycogen), for energy production (ATP), for the synthesis of innumerable metabolites, for signal transduction, for communication at the cellular and molecular levels, for the synthesis of nucleic acids, and they have many structural functions.
Application areas
In pharmacy and medicine (selection):
- For the treatment of hypoglycemia (low blood sugar).
- For parenteral nutrition (infusions).
- In drug design for the development of active substances (glycomimetics).
- As pharmaceutical excipients, for example, as thickening agents, as sweeteners, flavor corrigents and preservatives.
- As a tonic.
- For the treatment of diarrhea and vomiting in the form of oral rehydration solution.
- Dietary fiber for the treatment of constipation and softening the stool.
Dosage
Nutrition societies recommend that about 50% of daily energy needs be met with carbohydrates.
Adverse effects
Carbohydrates are essential for life and should not be considered unhealthy. However, excessive intake, for example in the form of sucrose, can lead to overweight and obesity. Many carbohydrates are cariogenic and can promote the development of tooth decay. Some carbohydrates, such as indigestible oligosaccharides, can cause digestive problems such as flatulence, abdominal pain, and diarrhea, especially in sensitive individuals.
