Sugar is a substance that is needed as fuel for our body. Sugar is the chemical name of a carbohydrate (saccharide). There are different types of saccharides, sugar is the collective name for these different types. Different types of sugar are first looked at at the molecular level to gain insight into the structure of different types of sugar. We also look at which foods contain certain types of sugars.
Monosaccharides
There are multiple forms of many monosaccharides. An example of this is the presence of mirror image isomers. These are molecules that have almost the same spatial structure, but are mirror images of each other. Sometimes these molecules have different chemical properties. Because it is not possible to check which form of a particular sugar is present in foods, this overview (with the exception of glucose) is limited to the general types of saccharides.
Glucose
Glucose is also known as grape sugar or dextrose. Glucose is a monosaccharide because it consists of one sugar molecule. Glucose can be easily digested and absorbed into the blood. The molecular formula of glucose is C6H12O6. Glucose exists in different forms, namely α-glucose and β-glucose. The difference between these shapes is the orientation of the OH group on the right side of the molecule.
Galactose
Galactose is also a monosaccharide. This is very similar to glucose, but the orientation of the OH groups is different. The spatial structure therefore differs, the molecular formula is the same as that of glucose, just like all other monosaccharides with six carbon atoms. Galactose is often present in dairy products as part of lactose.
Mannose
Mannose is a sugar found in certain fruits and vegetables, such as cranberries, apples, blueberries, green beans and tomatoes. This monosaccharide can be used to treat cystitis caused by the bacterium E. Coli, because this bacterium attaches to mannose. The human body itself is able to produce this substance from glucose. Mannose is not easily converted and stored, so a large part goes almost immediately into the blood and is then excreted.
Tagatose
Tagatose is a sugar that contains few calories, but tastes almost as sweet as glucose, for example. It occurs in dairy products. Tagatose is also a saccharide with six main carbon atoms.
Fructose
Fructose is also known as fruit sugar because this sugar is found in fruit. This is a monosaccharide that is more difficult to digest than glucose. Fructose must be converted into glucose in the liver to be digested. The molecular formula of fructose is like glucose C6H12O6, but the molecule has five main carbon atoms instead of six.
Ribose and 2-deoxyribose
Ribose and 2-deoxyribose are both monosaccharides, they differ in an OH group at the bottom right of the molecule. Ribose has one more OH group. These two monosaccharides form an important part of the nucleotides in our DNA and RNA. Nucleotides are the building blocks that make up DNA. DNA is a long molecule that contains hereditary information. RNA is used to copy hereditary information from the DNA, so that hereditary properties can become visible. Deoxyribose occurs in DNA molecules with the formula C5H10O4, ribose occurs in RNA molecules with the molecular formula C5H10O5.
Xylose
Xylose is a raw material for xylitol (a sweetener). Xylose is formed during the hydrolysis of wood dust with dilute acids. Xylose is not broken down and digested by the human body, so the substance is excreted. This monosaccharide has the same molecular formula as ribose.
Disaccharides
The second major group of sugars are disaccharides. These are sugar chains that are made up of two carbon rings (‘di’ stands for two). Disaccharides are therefore made up of two same or two different monosaccharides.
Sucrose
Sucrose is also known as table sugar, it is the most commonly used form of sugar in foods. Sucrose is extracted from sugar cane and sugar beets. A sucrose molecule consists of a glucose and fructose molecule, these molecules are bonded to each other (disaccharide). The molecular formula of sucrose is C12H22O11.
For the digestion of sucrose, the bond between the two molecules must first be broken.
Maltose
Maltose is also called malt sugar, which is created by cutting long sugar chains (polysaccharides) into short chains. Maltose is a disaccharide of two glucose molecules. This form of sugar is found in beer. The molecular formula is also C12H22O11.
Lactose
Lactose is also called milk sugar because it is found in milk products. Lactose is a disaccharide consisting of a galactose and glucose molecule. Lactose is difficult to digest, it even happens that people cannot digest lactose (lactose intolerant). The molecular formula of lactose, like maltose and sucrose, is C12H22O11.
Oligosaccharides and polysaccharides
In addition to these monosaccharides and disaccharides, there are also oligosaccharides and polysaccharides. These last two groups are saccharides that consist of several mono- and disaccharides. This can be imagined as a train consisting of several wagons, with the monosaccharides representing the wagons. Oligosaccharides consist of three to nine units and polysaccharides consist of nine or more units. Many combinations can be made of these different monosaccharides, so there are many oligo- and polysaccharides. For this reason, only one type of polysaccharide is discussed in our study: starch.
Starch is a long chain of glucose molecules. Rice, potatoes, pasta and bread consist mainly of starch. The structural formula of starch is therefore the multiple of the structural formula of glucose.
Processed sugars and sweeteners
Processed sugars are also called refined sugars. These processed sugars are cleaned in factories. This is done, for example, to make the sugar white in color, to have a neutral taste and to have a long shelf life. Unrefined sugars contain vitamins, enzymes, minerals and fiber. These substances are also removed during the process.
Sweeteners are substances that are not sugars, but do taste sweet just like sugars. An example of this is the stevioglycosides. These substances are extracted from the stevia plant. Sweeteners are not sugars that have been processed, but these are completely different substances.
