Prebiotics: Sources, Mechanisms, Types, Functions

Glenn Gibson and Marcel Roberfroid proposed the concept of prebiotics for the first time in 1955.

Prebiotics, non-digestible short-chain carbohydrates such as fibers, are a food source for gut bacteria that help healthy bacteria grow. Probiotics are live microorganisms that have significant benefits for our health.

Synthetic prebiotics are compounds added to some foods artificially and are present as a dietary supplement like powders and capsules. It improves their nutritional content and gut health. It also treats specific health conditions such as high blood sugar and more.

According to experts, It is also introduced as a “microbiome fertilizer”.

There are three most common prebiotics: Fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and trans-galacto-oligosaccharides (TOS).

The non-digestible plant fibers are called fructooligosaccharides, inulin, and galactooligosaccharides, which promote the growth and functions of good bacteria.

Moreover, not all fibers are prebiotics; however, all prebiotics are fibers. Nowadays, fructans and galactans, which make up the prebiotic carbohydrates in humans, are fermented by anaerobic bacteria in the large intestine.


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Sources of Prebiotics

Natural prebiotics are high in certain foods are as follows:

1. Chicory root

2. Dandelion greens

3. Raw leeks

4. Raw garlic

5. Raw Jerusalem artichoke

6. Raw or cooked onions

7. Raw jicama

8. Raw asparagus

9. Quinoa

10. Under-ripe bananas

11. Yacon syrup

12. Apples with skin, Bananas

13. Raw honey and Cow’s milk

14. Wheat dextrin

15. Psyllium husk

16. Whole-grain wheat

17. Barley

18. Oatmeal, Chia seeds

19. Whole-grain corn, beans

20. Peas

21. Soybean

What do prebiotics do?

Pancreatic and salivary amylase are the enzymes present in humans that digest some carbohydrates by breaking glycosidic linkages. However, these carbohydrates, such as oligosaccharides and polysaccharides, do not digest but act as a substrate for bacterial fermentation.

Many microorganisms, especially Bifidobacteria and Lactobacillus, live in the large intestine and ferment prebiotics. In addition, these gut bacteria are present in the stomach and small intestines.

When prebiotics (obtained from Plant-based foods) pass through the upper part of the gastrointestinal tract, they do not digest because our human body cannot break down them. So, it passes through the lower digestive tract. After it passes through the small intestine, it reaches the colon. It reaches undigested the colon, and then prebiotics get fermented by gut microorganisms that produce short-chain fatty acids such as butyrate, propionate, acetate, and gases. It provides nutrients to our colon cells, leading to a healthy digestive system.

These by-products improve the growth of native bacteria in the gastrointestinal tract and reduce pathogenic bacteria. Moreover, they support a healthy immune response and are innocuous to our body and gut health.

Types of Prebiotics with Functions

Most of the prebiotics are carbohydrates; however, some are non-carbohydrates. Prebiotics are of different types:

  1. Fructans
  2. Galactooligosaccharides
  3. Starch- and glucose-derived oligosaccharides
  4. Hemicellulose-derived oligosaccharides
  5. Pectic oligosaccharides
  6. Non-carbohydrate oligosaccharides

1. Fructans

    • Fructans are a polymer of fructose molecule and a type of small-chain carbohydrates or sugars. 
    • It consists of inulin and fructo-oligosaccharides (FOS) or oligofructose composed of a linear chain of fructose with β(2→1) linkage. 
    • It cannot be digested in the small intestine because humans do not have the fructan digestive enzyme. So, It can be fermented by the gut bacteria.
    • It can be present in many fruits and vegetables, such as onions, artichokes, garlic, ripe bananas, barley, wheat, rye, cereal, and grains. 
    • In addition, Fructans can also be added to foods to increase the fiber content.


    1. It has many health benefits. It helps in the protection against conditions like coronary heart disease, high blood pressure, diabetes, obesity, and some gastrointestinal disorders. It also prevents constipation and controls appetite.
    2. Inulin and fructooligosaccharides (FOS) can stimulate directly or indirectly many bacterial species.
    3. It also helps to improve the health of the gut microbiome.

    2. Galacto-oligosaccharides (GOS)

    • Galactooligosaccharides (GOS), the main component of prebiotics made up of plant sugars, are composed of galactosyl residues and terminal glucose linked by β-glycosidic bonds. 
    • It slightly stimulates Bifidobacteria and Lactobacilli, Enterobacteria, Bacteroidetes, and Firmicutes. 


    1. It helps in preventing eczema from developing, colic (Prevent excessive crying in infants, constipation, and obesity. 
    2.  It improves symptoms like stomach pain, cramps, and bloating in people who are lactose intolerant.

    3. Starch- and glucose-derived oligosaccharides

    • It is a type of starch resistant to small intestine digestion. 
    • Resistant starches are the combination of starch and products of starch degradation consisting of four main groups such as RS1, RS2, RS3, and RS4. 
    1. RS1- It is a physically inaccessible starch, such as starch in whole grains. 
    2. RS2- It is granular starch, such as starch in green bananas.
    3. RS3- It is a retrograded starch, such as starch in cooked and cooled potatoes.
    4. RS4- It is a chemically-modified starch, such as an esterified starch.
    • Polydextrose is a glucose-derived oligosaccharide that includes glucan with long branches and glycosidic linkages.


    1. Resistant Starch promotes health due to the production of a high level of butyrate.
    2. It stimulates the growth of beneficial bacteria, bifidobacteria, and lactobacilli within the gut.

    4. Hemicellulose-derived oligosaccharides

    The developing prebiotics are Hemicellulose-derived oligosaccharides (HDOs) such as Xylooligosaccharides (XOS) and mannooligosaccharides (MOS). 

    Xylooligosaccharides consist of short-chain sugar oligomers composed of xylose units. It consists of xylobiose, xylotriose, and xylotetraose. It can be obtained by enzymatic hydrolysis, xylan-degrading enzymes such as endo-β-1,4-xylanase, and xylan 1, 4-β-xylosidase.

    It is found naturally in fruits, vegetables, milk, honey, bamboo shoots, corn cob, wheat straw, sugarcane bagasse, and hardwood xylan.

    Mannooligosaccharides, a nonstarch hemicellulosic polysaccharide derived from mannan, is a short chain of repeating units of mannose linked by glycosidic bonds. 

    There are two forms: α- and β-MOS. The physicochemical hydrolysis of the cell wall of the yeast (Saccharomyces cerevisiae) can obtain α-MOS.

    The combined enzymatic hydrolysis of β-1, 4-mannanase, β-mannosidase, α-galactosidase, and β-glucosidase can generate β-MOS.

    It is also a second-generation prebiotic. It occurs in locust bean gum, konjac gum, and guar gum.


    1. low-value substrates such as locust bean gum, guar gum, and konjac gum 
    2. agro-wastes such as corn cob, copra meal, palm kernel cake, and corn cob


    1. It stimulates the growth of probiotics that improve the structural elements of the gut by decreasing pH.
    2. Arabinoxylans have the potent prebiotic activity to produce.
    3. It acts as a health promoter. It lowers the risk of various complex health problems.

    5. Pectic oligosaccharides

    • Some oligosaccharides obtained from a polysaccharide are known as Pectin. This type of oligosaccharide is called Pectin oligosaccharide (POS). 
    • Pectin oligosaccharides (POS), safe and non-mutagenic, are new potential prebiotics that have various health benefits.


    Orange, lemon, apple, beet pulp,


    1. Pectin oligosaccharides are used to treat gastrointestinal disorders, diabetes, and hypercholesterolemia. 
    2. It increases the probiotic flora in the gastrointestinal tract, such as Lactobacillus Eubacterium, Faecalibacterium, and Roseburia.
    3. It stimulates the apoptosis process in human colonic adenocarcinoma cells.
    4. It helps to protect cardiovascular tissues, reduce the damage caused by metals, and has anti-obesity effects, and antitoxic, antibacterial, and antioxidant activities.

     6. Non-carbohydrate oligosaccharides

    The non-carbohydrate oligosaccharides are cocoa-derived flavonols. As per the in vivo and in vitro experiments, Flavonols help stimulate lactic acid bacteria.

    Advantages of Prebiotics

    Prebiotics are innocuous to our gut health. The benefits of prebiotics are:

    1. Prebiotics help in the growth and function of gut microbiota. Moreover, Gut microbiota receives a source of energy from prebiotics. 
    2. It is beneficial for the immune system.
    3. It helps to change the gut environment.
    4. It controls the risk of colorectal cancer.
    5. It helps to prevent infant gastrointestinal disorders.
    6. It helps to control dermatitis problems, such as skin irritation.
    7. It helps to reduce the risk of cardiovascular disease.


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    About Author

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    Prativa Shrestha

    Prativa Shrestha is an enthusiastic person pursuing a master's degree in Food Microbiology from St. Xavier's College., Kathmandu. Currently, She is doing thesis work at Nepal Academy of Science and Technology (NAST). She loves to explore new ideas and showcase her creativity. She has also published two research articles. Moreover, She is interested in research fields like Food microbiology Biotechnology, and enzyme production.

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