OLIGOSACCHARIDES: CHARACTERISTICS, COMPOSITION, FUNCTIONS, TYPES - BIOLOGY - 2025

The oligosaccharides (from the Greek, oligo = little; sachar = sugar) are molecules composed of two to ten monosaccharide residues linked together by glycosidic bonds. Oligosaccharides come from a wide variety of food sources, such as milk, tomatoes, bananas, brown sugar, onion, barley, soy, rye, and garlic.

In the food industry and agriculture, much attention has been paid to oligosaccharides for their application as prebiotics, indigestible substances, beneficial thanks to the selective stimulation of the growth and activity of species of bacteria in the colon.

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These prebiotics are obtained from natural sources, or by hydrolysis of polysaccharides. The oligosaccharides in plants are glucose oligosaccharides, galactose oligosaccharides and sucrose oligosaccharides, the latter being the most abundant of all.

Oligosaccharides can also be found attached to proteins, forming glycoproteins, whose content by weight ranges from 1% to 90%. Glycoproteins play an important role in cell recognition, lectin binding, extracellular matrix formation, viral infections, receptor-substrate recognition, and antigenic determinants.

Glycoproteins have a variable carbohydrate composition, which is known as microheterogeneity. The characterization of the structure of carbohydrates is one of the goals of glycomics.

characteristics

Oligosaccharides, like other carbohydrates, are made up of monosaccharides that can be ketoses (with a keto group) and aldoses (with an aldehyde group). Both types of sugars have numerous hydroxyl groups, that is, they are polyhydroxylated substances, whose alcohol groups can be primary or secondary.

The structure of the monosaccharides that make up the oligosaccharides is cyclic, and they can be of the pyranose or furanose type. For example, glucose is an aldose whose cyclic structure is a pyranose. While fructose is a ketose whose cyclic structure is a furanose.

All monosaccharides that make up oligosaccharides have the D configuration of glyceraldehyde. Because of this, glucose is a D-glucopyranose and fructose is a D-fructopyranose. The configuration around the anomeric carbon, C1 in glucose and C2 in fructose, determines the alpha or beta configuration.

The anomeric group of a sugar can condense with an alcohol to form α- and β-glucoside bonds.

Nondigestible oligosaccharides (OND) have the β configuration, which cannot be hydrolyzed by digestive enzymes in the intestine and saliva. However, they are sensitive to hydrolysis by enzymes of bacteria in the colon.

Composition

Most oligosaccharides have between 3 and 10 monosaccharide residues. An exception is inulin, which is an OND that has much more than 10 monosaccharide residues. The word residue refers to the fact that when a glucoside bond is formed, between monosaccharides, there is elimination of a water molecule.

The composition of oligosaccharides is described later in the section on main types of oligosaccharides.

Features

The most common disaccharides like sucrose and lactose are a source of energy, in the form of adenosite triphosphate (ATP).

There is a steady increase in published scientific articles on the health properties of ONDs as prebiotics.

Some of the functions of ONDs that are prebiotic are to promote the growth of bacteria of the genus Bifidobacteria and to lower cholesterol. ONDs serve as artificial sweeteners, have a role in osteoporosis and in the control of diabetes mellitus 2, promote the growth of the intestinal microflora.

Furthermore, ONDs have been attributed properties such as reducing the risk of infections and diarrhea by reducing the pathogenic flora and enhancing the response of the immune system.

Types

Oligosaccharides could be divided into common and rare oligosaccharides. The former are disaccharides, such as sucrose and lactose. The latter have three or more monosaccharide residues and are mostly found in plants.

The oligosaccharides found in nature differ in the monosaccharides that compose them.

In this way, the following oligosaccharides are found: fructooligosaccharides (FOS), galactooligosaccharides (GOS); lactulooligosaccharides derived from galactooligosaccharides (LDGOS); xylooligosaccharides (XOS); arabinooligosaccharides (OSA); derived from seaweed (ADMO).

Other oligosaccharides include pectin-derived acids (pAOS), metallooligosaccharides (MOS), cyclodextrins (CD), isomalto-oligosaccharides (IMO), and human milk oligosaccharides (HMO).

Another way to classify oligosaccharides is to separate them into two groups: 1) primary oligosaccharides, which are found in plants, and are subdivided into two types based on glucose and sucrose; 2) secondary oligosaccharides that are formed from primary oligosaccharides.

Primary oligosaccharides are those that are synthesized from mono- or oligosaccharide and a glycosyl donor via a glycosyltransferase. Example, sucrose.

Secondary oligosaccharides are those formed in vivo or in vitro by hydrolysis of large oligosaccharides, polysaccharides, glycoproteins, and glycolipids.

Disaccharides

The most abundant disaccharide in plants is sucrose, made up of glucose and fructose. Its systematic name is O - α -D-glucopyranosyl- (1-2) - β -D- fructofuranoside. Because C1 in glucose and C2 in fructose participate in glycosidic bonding, sucrose is not a reducing sugar.

Lactose is made up of galactose and glucose, and is found only in milk. Its concentration varies from 0 to 7% depending on the species of mammal. The systematic name of lactose O - β -D-galactopyranosyl- (1-4) -D-glucopyranose.

Main oligosaccharides

Fructooligosaccharides (FOS)

The term fructooligosaccharide is frequently used for 1 ^F (1-β-Dfructofuranosyl) _n -sucrose, where n is 2 to 10 fructose units. For example, two fructose units form 1-basketose; three units form 1-nistosa; and four units form 1-fructofuranosyl-nistose.

FOS are soluble and slightly sweet fibers, form gels, exhibit resistance to enzymes involved in digestion such as alpha-amylase, sucrase and maltase. They are present in cereals, fruits and vegetables. They can also be extracted from various sources by enzymatic reactions.

Among the health benefits are the prevention of intestinal and respiratory tract infections, increase the response of the immune system, stimulate the growth of Lactobacilli and Bifidobacteria species, and increase the absorption of minerals.

Galactooligosaccharides (GOS)

Galactooligosaccharides are also called transgalactooligosaccharides. Generally, GOS molecules can be represented as: Gal ^X (Gal) _n ^Y Glc.

Where Gal is galactose and n is the β -1,4 bond that joins the galactose residues. Furthermore, the formula indicates that β-galactosidases also synthesize other bonds: β - (1-3) and β - (1-6).

GOSs are produced from lactose by transgalactosylation catalyzed by β-galactosidases. Mammalian milk is a natural source of GOS. GOS promote the growth of bifidobacteria.

GOSs are commercially produced under the name Oligomate 55, which is a preparation based on β-galactosidases from Aspergillus oryzae and Streptoccoccus thermophilus. It contains 36% of tri, tetra-, penta- and hexa-galacto-oligosaccharides, 16% of the disaccharides galactosyl-glucose and galactosyl-galactose, 38% of monosaccharides, and 10% of lactose.

Although the composition of GOSs, produced commercially, can vary according to the origin of the β-galactosidase that they use. The companies FrieslandCampina and Nissin Sugar use the enzymes from Bacillus circulans and Cryptococcus laurentii, respectively.

Among the benefits of consuming GOS are the rearrangement of the intestinal flora, the regulation of the intestinal immune system and the reinforcement of the intestinal barrier.

The oligosaccharides lactulose, tagatose and lactobionic acid can also be obtained from lactose, by using oxidoreductases.

Xylooligosaccharides (XOS)

XOS are composed of xylose units linked by β - (1-4) bonds. Polymerizes between two and ten monosaccharides. Some XOS may have arabinosyl, acetyl, or glucuronyl motifs.

XOSs are produced enzymatically by hydrolysis of xylan from birch bark, oats, kernel, or inedible part of corn. XOSs are mainly used in Japan, under the approval of FOSHU (Foods for Specific Health Use).

Feruloyl xylooligosaccharides or oligosaccharides are present in wheat bread, barley husk, almond shells, bamboo and kernel, inedible part of corn. XOS can be extracted by the enzymatic degradation of xylan.

These oligosaccharides have the property of reducing total cholesterol in patients with type 2 diabetes mellitus, colon cancer. They are bifidogenic.

Arabinooligosaccharides (OSA)

OSA is obtained by hydrolysis of arabinan polysaccharide that has α - (1-3) and α- (1-5) linkages of L-arabinofuranose. Arabinose is present in arabinan, arabinogalactans, or arabino xylan, which are components of the plant cell wall. The type of AOS link depends on the source.

OSA reduces inflammation in patients with ulcerative colitis, also stimulates the growth of Bifidobacterium and Lactobacillus.

Isomalto-oligosaccharides (IMO)

The structure of IMO consists of glycosyl residues linked to maltose or isomaltose via α- (1-6) bonds, the most abundant being raffinose and stachyose.

IMO is produced in the industry under the name Isomalto-900, which consists of incubating α -amylase, pullulanase and α -glucosidase with corn starch. The main oligosaccharides in the resulting mixture are isomaltose (Glu α -1-6 Glu), isomaltotriose (Glu α -1-6 Glu α -1-6 Glu) and panose (Glu α -1-6 Glu α -1-4 Glu).

Among the health benefits is the reduction of nitrogenous products. They have an antidiabetic effect. They improve lipid metabolism.

Applications of prebiotics in colon cancer

It is estimated that 15% of the factors that influence the appearance of this disease have to do with lifestyle. One of these factors is diet, it is known that meat and alcohol increase the risk of the appearance of this disease, while a diet rich in fiber and milk reduce it.

It has been shown that there is a close relationship between the metabolic activities of intestinal bacteria and tumor formation. The rational use of prebiotics is based on the observation that bifidobacteria and lactobacillus do not produce carcinogenic compounds.

There have been many studies in animal models and very few in humans. In humans, similar to animal models, it was shown that the consumption of prebiotics produces a significant reduction in colon cells and genotoxicity, and increases the function of the intestinal barrier.

Applications of prebiotics in inflammatory bowel disease

Inflammatory bowel disease is characterized by uncontrolled inflammation of the gastrointestinal tract. There are two related conditions, namely: Crohn's disease and ulcerative colitis.

Using animal models of ulcerative colititis, the use of broad-spectrum antibiotics was shown to prevent the development of the disease. It is important to emphasize that the microbiota of healthy individuals is different from those with inflammatory bowel disease.

Due to this, there is a special interest in using prebiotics to reduce the inflammatory condition. Studies carried out in animal models showed that the consumption of FOS and inulin significantly reduces the pro-inflammatory immune markers of the animals.

Oligosaccharides in glycoproteins

Blood plasma proteins, many milk and egg proteins, mucins, connective tissue components, some hormones, integral plasma membrane proteins, and many enzymes are glycoproteins (GP). Generally, the oligosaccharide in GPs has on average 15 monosaccharide units.

Oligosaccharides are attached to proteins by N-glucosidic or O-glycosidic bonds. The N-glucosidic bond, consists of the formation of a covalent bond between N-acetyl-glucosamine (GlcNAc) and the nitrogen of an amide group of the amino acid residue asparagine (Asn), which is commonly found as Asn-X- Ser or Asn-X-Thr.

Glycosylation of proteins, binding of oligosaccharides to protein, occurs simultaneously with protein biosynthesis. The exact steps of this process vary with the identity of the glycoproteins, but all N-linked oligosaccharides have in common a pentapeptide with the structure: GlcNAcβ (1-4) GlcNAcβ (1-4) Man ₂.

The O -glycosidic union consists of the union of the disaccharide β -galactosyl- (1-3) - α - N -acetylgalactosamine to the OH group of a serine (Ser) or a threonine (Thr). O-linked oligosaccharides vary in size, for example they can reach up to 1000 disaccharide units in proteoglycans.

Role of oligosaccharides in glycoproteins

The carbohydrate component in GPs regulates numerous processes. For example, in the interaction between sperm and egg during fertilization. The mature ovum is surrounded by an extracellular layer, called the zona pellucida (ZP). The receptor on the sperm surface recognizes oligosaccharides attached to ZP, which is a GP.

Interaction of the sperm receptor with the ZP oligosaccharides results in the release of proteases and hyaluronidases. These enzymes dissolve ZP. In this way the sperm can penetrate the egg.

A second example is oligosaccharides as antigenic determinants. ABO blood group antigens are glycoprotein oligosaccharides and glycolipids on the surface of an individual's cells. Individuals with type A cells have A antigens on their cell surface, and they carry anti-B antibodies in their blood.

Individuals with type B cells carry B antigens and carry anti-A antibodies. Individuals with type AB cells have A and B antigens and do not have anti-A or anti-B antibodies.

Type O individuals have cells that do not possess any antigen, and have anti-A and anti-B antibodies. This information is key to performing blood transfusions.

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