What are monosaccharides?

According to the size, monosaccharides are classified into three major groups: monosaccharides, oligosaccharides, and polysaccharides.

Monosaccharides are carbohydrates that cannot be further hydrolysed to simpler units having the basic formula Cn(H2O)n, where n=3 or more. Monosaccharides can by combined through glycosidic bonds to form larger carbohydrates, known as oligosaccharides or polysaccharides.

Monosaccharides, the simplest type of carbohydrates, are often called simple sugars (sucrose), containing three to seven carbon atoms, and serve as the building blocks for larger molecules. Since they have multiple asymmetric centers, many types of isoforms are possible, including enantiomers, diastereoisomers, and epimers.

There are 3 monosaccharides: glucose, fructose, galactose.

Fructose (or levulose) is a simple sugar (monosaccharide) found in many foods. It is a constituent of disaccharides sucrose. It can be covered into glucose in the liver. Honey, tree fruits, berries, melons and some root vegetables, such as beets, sweet potatoes, parsnips and onions, contain fructose, usually in combination with sucrose and glucose.

Glucose (C6H12O6) is one of the most common monosaccharides in nature, used by nearly every form of life. It is one of the most important monosaccharides, which is synthesized during photosynthesis and serves as the ‘fuel’ and source of energy, stored as a polymer glycogen in animals and as starch in plants.

Galactose binds to glucose to form the disaccharide lactose. It can be converted into glucose in the liver. Galactose widely distributed in plant gums and pectins and is found in milk sugar (the disaccharide lactose).

The last large class of carbohydrates are polysaccharides, commonly known as glycans. They are complex carbohydrates composed of large number of monosaccharides linked together covalently by glycosidic bonds, which can be linked linearly in a chain or branch laterally forming complex polymers.
What are monosaccharides?

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Fructose as sweetener

Fructose, a sweetener that is monosaccharide found naturally in fresh fruit and honey. It is obtained by the inversion of sucrose by means of the enzyme invertase and by the isomerization of corn syrup.

Fructose is an established sweetener for diabetics and is used in several countries. Of the natural sugars other than sucrose used by humans, fructose is the sweetest (nearly twice as sweet as table sugar, sucrose) and it is the most water soluble. It is hygroscopic, making it an excellent humectant when used in baked goods.

Food manufacturers became interested in fructose as an alternative sweetening agent because fructose is the sweetest of all sugars commonly found in nature. Finding an inexpensive source of fructose, they reasoned, would allow them to replace sucrose and therefore reduce their production costs.

However while the monosaccharide form of fructose is found naturally in many fruits and vegetables, there are very few natural sources that would be available on a large scale. Eventually a process was developed in which glucose was converted to fructose using natural enzymes.

An early effort at creating a fructose sweetener was patented in 1935. This process relied in extraction of fructose (also known as levulose) from plants including Jerusalem artichoke, dahlias, chicory, and beet sugar molasses.
Fructose as sweetener 

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The Sweetness of Sugar

Sweetness is a taste which is generally pleasing to humans as well as to many other animals. Sweetness is found in many forms, the most common being the simple sugars.

In United States, the natural sugars of milk, fruits, vegetables, and grains account for about half of the sugar intake, the other half consists of concentrated sugars that have been refined and added to foods for a variety of purposes.

Sugars, important in nutrition, consist of monosaccharides, having the general formula C6H12O6, and disaccharides, having the general formula C12H22O11.

Although the monosaccharides consists of 3-carbon sugars (trioses), 4-carbon sugars (tetroses), 5-carbon sugars (pentoses), and 6-carbon sugars (hexoses), only the latter are important in human nutrition as sources of energy.

Three monosaccharides are important in nutrition: glucose, fructose and galactose. All three monosaccharides have the same number and kinds of atoms but in different arrangements.

Glucose, a 6-carbon sugar, is one of the simplest carbohydrates found in foods. While many foods contain traces of glucose, it is found in significant amounts only in fruits, such as grapes.

Most cells depend on glucose for their fuel to some extent and the cells of the brain and the rest of the nervous system depend almost exclusively on glucose for their energy.

Fructose, also a 6-carbon sugar, is found in ripened fruits and honey, both of these sugars can be utilizes by body as a source of energy. It is the sweetest of the natural sugars.

Other source of fructose include soft drinks, ready to eat cereals and other products sweetened with high fructose corn syrup.

Lactose, the 12-carbon sugar present in milk, is broken down in the intestine to glucose and lactose (6-carbon sugar), both of which can be used as sources of energy.

Maltose, another disaccharide, produced form starch in the malting of grains is much less effective sweetener than sucrose.

The used of added sugars had risen steadily over the past several decades, both in the United States and around the world, with soft drinks and sugared fruit drinks accounting for most of the increase.
The Sweetness of Sugar

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