Dextrose is a reducing sugar

The human body gains more than 50 percent of its energy from carbohydrates. The body also uses them to build other substances such as proteins or fats. They are oxidized in the brain, in the muscles or in other organs with the help of blood oxygen, and energy is released in the process. The breakdown of carbohydrates takes place during digestion with the help of enzymes that break down long-chain molecules into short-chain ones. The energy can be obtained more easily from these. Carbohydrates are produced by plants during photosynthesis. The chlorophyll of the green leaves converts carbon dioxide and water into carbohydrates with the help of light energy, at the same time oxygen is produced, which humans and animals need. The plants store the energy mainly in the form of starch.


The misleading term "hydrate" was incorrectly created in the past because it was thought that carbohydrates contained water. carbohydrates are made up of carbon atoms connected to hydrogen and oxygen atoms. They split off water when they combine with each other. The simple sugars or the Monosaccharides represent the basic building blocks for all carbohydrates. They are verified in the chemical laboratory with the Fehling test. Simple sugars such as glucose or fructose occur as chain-shaped and ring-shaped molecules.

Ring shape: The carbon atoms in the ring are not shown,
they are each located at the connection points.

Some sugar molecules form isomers: In the alpha-Form that α-Glucose (and also with the α-Galactose), the two OH groups are on the C1-Atom and at the C2-Atom in the plane of the ring on the same side. In the beta-Form that β-Glucose, they face each other. In addition to the ring shape, there are also open-chain shapes that are also isomeric to the ring shape:

The open-chain forms contain an aldehyde group that has a reducing effect. This explains why, for example, glucose, like an aldehyde, can reduce a silver nitrate solution to elemental silver. In aqueous solution there is usually a mixture of the various ring and open-chain forms. They are then in equilibrium with one another.


The common sugar that is widespread in the household is called beet sugar or cane sugar, depending on its origin. Beet sugar is obtained from sugar beet, while cane sugar is obtained from sugar cane. This sugar is one of the double sugars; chemists know it as sucrose. The double sugar or the Disaccharides arise when two simple sugars combine with elimination of water. In sucrose, one glucose and one fructose molecule are linked to one another by an oxygen bridge. Malt sugar, or maltose, requires two glucose molecules. In milk sugar, lactose, a glucose and a galactose molecule are linked to one another.

The Fehling's test and the silver mirror test have negative results for sucrose, since the linkage does not allow the ring to open. Sucrose therefore does not have a reducing effect. In contrast, in the case of maltose and lactose, the C1-Atom of the glucose building block with the free OH group a ring opening takes place. This forms an aldehyde group. Therefore, the Fehling's test and the silver mirror test for maltose and lactose are positive, both have a reducing effect.


In natural starch, sugar units are linked to form long chains. Starch like potato or corn starch is made up of multiple sugars and is known as Polysaccharides. The sugar units represented by a hexagon in the graphic can form chains with several hundred chain links in terms of strength. In amylose, the chains form a helical arrangement that are linked to one another by oxygen atoms. Natural potato starch consists of around 20 percent water-soluble amylose and 80 percent water-insoluble amylopectin. In amylopectin, the sugar units are not connected in a helical manner, but rather in branched chains.



When chewing on white bread for a long time, the enzyme amylase breaks down the chains in the saliva, and shorter chains are obtained. The resulting dextrins can be recognized by their sweet taste. The chains can also be broken down into short sections or into individual sugar units by heating or adding acid. Amylopectin and amylose molecules form a cross-linked structure in the starch. This creates the typical starch grains (visible under the microscope). The amylose is located in the core. The firm shell of the starch grain is built up by amylopectin.



At room temperature, water molecules cannot penetrate through the shell of the starch granules. They only adhere to the surface of the shell. When heated, the amylopectin begins to swell and it absorbs water. The shell becomes so permeable that the water reaches the amylose and it dissolves in the water. The combination of these two effects creates the typical gelatinization of the starch that occurs from 60 to 70 ° C. The soluble starch available in the laboratory is a processed product, it only contains amylose. Compared to starch, the polymer cellulose forms long, unbranched chains. The swellability of cellulose is not as good as that of starch, since no water molecules can store in the macro-molecule of cellulose.

Cellulose is the most abundant natural polymer found in nature and also the most abundant organic compound. Cellulose, together with lignin and pectins, forms the structural substance for plant cell walls. With the exception of a few tunicates, cellulose cannot be found in animals. The macro-molecule of cellulose is made up of the double sugar cellobiose. A cellobiose molecule contains two basic units of glucose, which are separated by one βLink are connected to each other. Cellulose polymers contain up to 5000 glucose units. The hydrogen bonds between the macro-molecules prevent the molecule from spiraling.



Humans cannot obtain energy from cellulose because their enzymes do β-Not able to disassemble links. However, the bacteria in the rumen of ruminants are able to do this. The cellulose is excreted undigested through the human intestine. However, it is not "ballast", as was previously assumed, but is of great importance as dietary fiber: It promotes bowel activity and loosens stool. High fiber foods prevent colon cancer and cardiovascular disease. They mainly include pulses and cereals, but vegetables and fruits also contain fiber.
foodper 100 grams
energyKilojoulescarbohydratesusablefrom thatFructosefrom thatglucosefrom thatSucroseBallast-fabrics
Rice grain1443 74,10,08 0,080,082,2
wheat flour
Type 405
1403 71,00,070,070,284,0
Bee honey1367 81,038,833,95,00
Whole wheat flour
1225 59,00,060,060,9013,9
Potatoes285 14,80,150,220,302,1
Apple225 11,45,742,042,552,0
Lettuce48 1,10,530,420,101,4
Distribution of carbohydrates in food, all values ​​in grams, based on 100 grams
These values ​​are didactically prepared, they are not considered a reference for people with intolerance.

A nutritional table shows how much energy can be obtained from a food. The starch content can be roughly calculated in the table above by subtracting the values ​​for the three sugars from the usable carbohydrates. Humans and animals not only use the carbohydrates as direct energy suppliers, but they also store them in the form of glycogen in the muscles and in the liver. Glycogen is a polysaccharide similar to amylopectin, but it is even more branched and forms even larger molecular masses. A glycogen molecule can contain up to 100,000 glucose building blocks. If necessary and also during sleep, the glycogen supply is broken down again into glucose. The liver is shown in dark red on the graphic at the top.

Create your own book: basic text carbohydrates


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