Glycosaminoglycans

Glycosaminoglycans (GAGs) are linear, complex and polydisperse polysaccharides that are made by all animal cells.

They are generally associated with a small amount of protein, forming proteoglcycans, which typically consist of over 95 percent carbohydrate. They include hyaluronan or hyaluronic acid, chondroitin sulfate, dermatan sulfate, keratan sulfate and heparan sulfate.

Glycosaminoglycans have a special ability to bind large amounts of water, thereby producing the gel-like matrix that forms the basis of the body’s ground substance.

Glycoaminoglycans

Glycosaminoglycans are long, unbranched, heteropolysaccharides chains generally composed of a repeating disaccharide unit in which one sugar either N-acetylgalactosamine or N-acetylglucosamine.

Typically, each disaccharide carries a carboxyl group and often one or more sulfates so that most glycosaminoglycans have a high density of negative charges.

Glycosaminoglycans support connective tissues such as skin, tendons, cartilage, ligaments, and bone.

Glycosaminoglycans also support the structure do ears, auditory tubes and heart valves. Glycosaminoglycans such as chondroitin sulfate are jelly0like substance that helps lubricate surfaces of joints and provide resiliency, so that joints resist compression.
Glycosaminoglycans

Polysaccharide of chitin

Chitin is a major structural polysaccharide found in inveterate animals and lower plants. It is widely available biopolymer obtained principally from shrimp and crab shell waste.

It is occurs as highly ordered microfibrils in many species, in a variety of arrangements, from diatom spines to cell was components of many fungi and yeasts.

Chitin is a type of polysaccharide composed of an amino sugar and consisting of a straight chain molecule by binding D-glucosamines in which each amino sugar is acetylated by β-1,4 linkage.

Chitin

Among the three forms, α-chitin is the most abundant, crystalline, tightly compacted and stable form in which the chains are arranged in an anti-parallel fashion. α-chitin is found where extra hardness proves essential, whereas β- and γ-chitin provide toughness, flexibility and mobility.

Chitin is considered the second most plentiful biomaterial following cellulose. When chitin is deacetylated to about 50% of the free amine form, it is referred to as chitosan.

Chitin is produced by removing calcium carbonate and proteins from the shells. In the production of chitin, calcium carbonate is first dissolved by stirring the shells in dilute hydrochloric acid at ambient temperature.

Proteins are then extracted from the decalcified shells by threatening them with dilute aqueous sodium hydroxide; crude chitin is then obtained.
Polysaccharide of chitin

What is heteropolysaccharides?

Heteropolysaccharides, also called heteroglycans are the polymers made from more than one kind of monosaccharides or monosaccharides derivatives. Although a few representatives contain three or more different monosaccharides, most naturally occurring heteroglycans contain only two different ones and are closely associated with lipid or protein.

Heteropolysaccharides are involved with viral and bacterial attachments to cells, the immune system, the migration of normal cells, the migration of cancerous cells, the fertilization of ova, and the changes in cells during tissue development. The most important heteropolysaccharides are as follows:
Neutral heteropolysaccharides
Neutral heteropolysaccharides contain monosaccharides and the acetylated amino-nitrogen in their molecules and are known as acetyl glucosamines. The most important acetyl glucosamine of animal cells is the chitin which is an important constituent of the cells of the crustaceans and some insects.

Acidic heteropolysaccharides
Contain different kinds of monosaccharides and sulphuric or other acids. The most important are hyluronic acid, chondroitin sulphate and heparin.
Their functions are:
*Heparin – anticoagulant
*Hyaluronic acid –water binding, lubricant, shock absorber
*Chondroitin-4-sulphate – calcium accumulation, cartilage and bone formation

Mucoproteins and glycoproteins
When the acetyl glucosamines, monosaccharides and protein unite together they form mucoproteins and glycoproteins. These include the blood group polysaccharides which specified the blood group and gamma globulin –which function as antibody
What is heteropolysaccharides?

Homopolysaccharides

Homopolysaccharides are composed of just one type of monosaccharide and heteropolysaccharides are built from more than one type.

The homopolysaccharides cellulose is of major importance to the structure of plants because it provides support to stems and stalks and provides a tough and water–insoluble protective barrier.

In general, homopolysaccharides have a well defined chemical structure, although their molecule weight of an individual amylose or xylan molecule may vary within a particular range, depending on the source.

Several naturally occurring homopolysaccharides are listed in the following table:
Cellulose
Amylose
Chitin
Inulin
Xylan
Glycogen
Amylopectin
Dextran
Agar

Cellulose consists of a long chain of β-glucopyranose residues joined by β-(1 – 4) glycosidic bonds. The strength of cellulose comes from the way in which cellulose molecules from hydrogen bonds with neighboring ones, producing durable sheets of polysaccharides.

There are two types of homopolysaccharides
*Linear homopolysaccharides – Polysaccharides formed from a single sugar unit and having straight chain structure.

*Branched homopolysaccharides – For the most part, these polysaccharides serve as energy reserves and not as structural elements.
Homopolysaccharides

Glycosidic bond

Polysaccharides chains are generally formed by a repeated sequence of monomers or oligomers. Few monosaccharides exist in the free state. They generally occur linked by glycosidic bond to one another or to an aglycones.

The term ‘glycosidic bond’ is used for the bond between the anomeric C-atom and the glycosidic O (N-, S,) atom.

While the term ‘glycosidic linkage' is used to define a set of all bonds that connects to monosaccharide rings.

It is a bond that links two sugar units together; it is formed between the free carbonyl group of one sugar and a hydroxyl group of another sugar; the orientation (α or β) and position (eg. 1,4) of the link must be specified. The structure of a di-, oligo- or polysaccharide sugar is based on the bonding of two monosaccharides.

In the case of a disaccharide, two monosaccharides are joined with loss of one molecule of water. This joining occurs between two –OH groups, one of each monosaccharide.
Glycosidic bond

Gums

Gums are defined as water soluble or swellable polysaccharides and polysaccharides derivatives. 

Polysaccharides are used in the food industry because they are widely available, usually of low cost and non toxic.

Distinct from polysaccharides that form gels are a group of polysaccharides that are called gums.

The principal property of polysaccharides gums is they have a high affinity for water and give high viscosity aqueous solutions, but are not able to form gel.

The reason for this is that all gums possess structures that incorporate a very high degree of branching or highly interrupted chains.

This prevents the formation of junction zones that are a feature of polysaccharide gels.

Gums are used by the food industry to thicken, increase viscosity of gel, stabilize, and/or emulsify certain processed foods. They generally thicken or gel aqueous systems at low concentrations.

Gums commonly used in foods are starches, cellulose derivatives, guar gum, locust bean gum, pectin, algin, carrageenan, xanthan and gum arabic and to a much lesser extent agar and gums, ghatti, karaya and tragacanth.

They impart body, texture, and mouthfeel to foods, while also making it less likely that dispersed ingredients will separate.

Gums are also used in many frozen products because they control crystal growth, yield optimal texture, and make the food more stable in the freezing and thawing process.
Gums

Polysaccharides

Combinations of more than two sugars are often referred to as oligosaccharides, unless they are very large and then they are called polysaccharides.

Raffinose and stachyose are two oligosaccharides of interest because they are hard to digest.

Raffinose contains one molecule each of glucose, fructose and galactose. Stachyose is very similar to raffinose except it contains two molecules of galactose.

Polysaccharides, also called glycans, consist of monosaccharides and their derivatives. If a polysaccharides contains only one kind of monosaccharides molecule, it is homopolysaccharides or homoglycan, whereas those containing more than one kind is monosaccharide are heteropolysaccharides.

In human, polysaccharides function as storage materials, structural components, or protective substances. This starch, glycogen and other storage polysaccharides, as readily ,metabolized food, provide energy reserves for cells.

Polysaccharides may be added to foods for a variety of reasons. Nutritionally, they are generally added to increase the dietary fiber content.

Functionally, polysaccharides are added to thicken, form gels, bond water and stabilize proteins.

Agarose and carrageenan can be used to produce gels. Agarose has been used in microbiology for more than 100 years to reinforce culture media (“agar-agar”).

Starch is the most common polysaccharides added to food products. For some uses, starch may chemically modified to improve stability or to alter its functional properties.

Inulin, a fructose polymer is used as a starch substitute in diabetics; dietary products. It also serves as a test substance for measuring renal clearance.

Cellulose and cellulose derivatives are also added to a number of food products. The term “gum” is used to describe some do the naturally occurring polysaccharides added to food.

Chitin, is the most important structural substance in insect ad crustacean shells, and is this the most common animal polysaccharides.

Some naturally occurring polysaccharides added to foods include: agar, gum tragacanth, algin, locust bean gum, carrageenan, starch, cellulose, pectin, guar gum, xanthan gum, and gum arabic.
Polysaccharides