Oligosaccharides: Definition, Classification, Biological Functions and Examples (2024)

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What is an Oligosaccharide?

Oligosaccharides are compounds polymerized by 2-10 glycosidic bonds, where the glycosidic bond is formed by the dehydration condensation of the glycosidic hydroxyl group of one monosaccharide with one of the hydroxyl groups of another monosaccharide. They are usually bound to proteins or lipids in the form of glycoproteins or glycolipids, having small aggregates of 2-4 monosaccharides linked together. Oligosaccharides are divided into functional oligosaccharides and common oligosaccharides, with the common characteristics of being difficult to be digested and absorbed in the gastrointestinal tract, low sweetness, low calories, and basically no increase in blood glucose and blood lipids. The most prevalent oligosaccharides are disaccharides, which are two monosaccharides bound by a glycosidic bond. The main types of covalent bonds for oligosaccharides include N-glycosidic and O-glycosidic types.

• N-glycosidic type oligosaccharides are linked through the amino group of Asn on the polypeptide, and there are high mannose, heterozygous and complex types.
• N-glycosidic bonding type oligosaccharides are connected through the hydroxyl group of Ser or Thr on the polypeptide chain, or with the hydroxyl group of membrane lipids.

Fig. 1. Chemical structure of oligosaccharides. (a) Chitooligosaccharides (COS), (b) carboxylated COS (CCOS), (c) carrageenan. (M, A, Eisa.; et al, 2021)

Difference Between Monosaccharide and Oligosaccharide

Monosaccharides and derivatives of oligosaccharides play a crucial role in biological processes. Monosaccharides serve as the basic unit of carbohydrates and include glucose, xylose and fructose. Oligosaccharides, on the other hand, consist of 2 to 10 monosaccharides and cover structures such as disaccharides and trisaccharides. In addition to this, monosaccharides, oligosaccharides and their derivatives possess diverse biological properties including, but not limited to, anticancer, antiviral, insecticidal, antimicrobial and antioxidant activities. The biological functions of these molecules provide critical support for many aspects of life-sustaining processes.

Classification of Oligosaccharides

Maltodextrin Oligosaccharide: It possesses characteristics of easy digestion, low sweetness, and low osmotic pressure, extending the energy supply time and enhancing muscle endurance and anti-fatigue capabilities. After intense physical activity or strenuous exercise, the body is prone to dehydration, reduced energy reserves, decreased blood glucose consumption, elevated body temperature, impaired muscle-nerve conduction, and disrupted brain function, leading to various physiological changes. Consuming maltodextrin oligosaccharide helps maintain blood glucose levels, reduce lactic acid production, and promote insulin balance. Scientific experiments have demonstrated that the use of oligosaccharides can significantly increase endurance and functional capacity by more than 30%.

Isomaltooligosaccharide: It is known as the bifidus factor, acting as a proliferation factor for bifidobacteria when it enters the colon. It effectively stimulates the growth of beneficial bacteria, particularly bifidobacteria, while inhibiting the growth of harmful putrefactive bacteria. Long-term consumption can slow down aging, promote bowel movements, inhibit harmful bacterial populations, prevent cancer, exhibit anti-cancer properties, reduce the burden on the liver, and enhance nutrient absorption. It has a positive impact on the absorption of ions such as calcium, iron, and zinc, improving the digestion of lactose and lipid metabolism. The higher the oligosaccharide content, the more pronounced its nutritional and health benefits for the human body.

Biological Functions of Oligosaccharides

• Oligosaccharides promote the balance of the human microbiota, aiding in the increase of beneficial bacteria such as bifidobacteria. Through metabolism, they generate organic acids, lowering the intestinal pH, thereby inhibiting the proliferation of Salmonella and putrefactive bacteria. This helps regulate gastrointestinal function, suppress the formation of putrefactive substances, improve stool consistency, prevent and alleviate constipation, while also enhancing vitamin synthesis and boosting immune function.
• Oligosaccharides, similar to water-soluble plant fibers, contribute to improving lipid metabolism, reducing the accumulation of cholesterol and triglycerides in the bloodstream.
• Oligosaccharides fall under the category of non-insulin-dependent compounds, causing no elevation in blood sugar levels, making them suitable for individuals with high blood sugar and diabetes.
• Due to the difficulty of oligosaccharides being hydrolyzed by salivary and small intestine digestive enzymes, they have a lower calorific content, reducing the likelihood of fat conversion.
• Oligosaccharides do not provide a substrate for the growth of cariogenic bacteria and do not exhibit a bacterial agglutination effect, aiding in the prevention of dental caries.

Fig. 2. Synthesis of human milk oligosaccharides. (M, Y, Lu.; et al, 2021)

Therefore, as a food ingredient, oligosaccharides find extensive applications in dairy products, probiotic beverages, bifidobacterium yogurt, cereal foods, and health foods, with a particular emphasis on applications in infant and elderly nutrition. In the health food category, there are also oral liquids primarily composed of oligosaccharides, designed to directly regulate intestinal microbiota, promote intestinal regularity, adjust lipid metabolism, and enhance immune function. Owing to the poor digestibility and minimal energy content of oligosaccharides in the human body, they are extensively used in low-energy foods, including weight loss products, diabetic-friendly foods, and those designed for individuals with hypertension.

Common Oligosaccharides

• Arabinoxylan oligosaccharides derived from grains are a type of oligosaccharide.
• Oligofructose (FOS) or fructooligosaccharide s found in plants like Jerusalem artichoke, onions, and canned foods, as well as galactooligosaccharides (GOS) such as cottonseed sugar, water-soluble sugar in lamb's quarters, raffinose in soybeans, and trans-galactooligosaccharides (TOS), are various oligosaccharides obtained from different sources.
• Bitter glucan oligosaccharides produced by pustulan fall into the category of oligosaccharides, while oligoglucose, derived from sucrose production, is another oligosaccharide.
• Human milk oligosaccharides (HMO) are naturally found in breast milk, and isomaltooligosaccharides (IOS) are oligosaccharides produced from starch.
• Lactulose is an oligosaccharide produced from lactose and sucrose.
• Maltotriose is formed during the digestive process and is present in liquid glucose and brown rice syrup.
• Mannooligosaccharides (MOS) are artificially produced oligosaccharides.
• Additionally, there are oligosaccharides derived from honey disaccharides, N-acetyl chitosan oligosaccharides (from chitosan), pectin oligosaccharides (from pectin), and xylooligosaccharides (produced from corn cobs and birch wood).

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