Fructooligosaccharides (FOS) and Inulin
Fructooligosaccharides (FOS), also known as fructans, are one of the most well-known and widely studied classes of oligosaccharides. They consist of short chains of fructose units, often terminating in a glucose unit. Inulin is a longer chain fructan that is often considered part of the same family.
FOS is a prebiotic, meaning it resists digestion in the upper gastrointestinal tract and travels intact to the colon, where it ferments and feeds beneficial gut bacteria, primarily Bifidobacteria. This fermentation process produces short-chain fatty acids (SCFAs), which support gut health.
Natural Sources of FOS and Inulin
FOS and inulin are found naturally in a variety of plants, with some of the richest sources including:
- Chicory root, which is a common commercial source for inulin extraction
- Jerusalem artichokes
- Yacón root
- Garlic and onions
- Leeks and asparagus
- Bananas and other fruits
- Wheat and other cereals
Raffinose Family Oligosaccharides (RFOs)
The raffinose family of oligosaccharides (RFOs) are another highly abundant group of carbohydrates in the plant kingdom, ranking second only to sucrose in abundance among soluble carbohydrates in many plants. RFOs are derived from sucrose by adding one or more α-galactosyl units. The most common RFOs are raffinose, stachyose, and verbascose.
These oligosaccharides are notable for their presence in legumes, which is responsible for the flatulence many people experience when consuming them. Humans lack the enzyme α-galactosidase needed to digest these sugars, so they are fermented by bacteria in the large intestine. RFOs also serve crucial physiological roles in plants, such as acting as storage carbohydrates and conferring tolerance to stress like desiccation and cold.
Where RFOs are Most Abundant
- Legumes: Lentils, chickpeas, soybeans, peas, and beans are particularly rich sources.
- Vegetables: Cabbage, broccoli, and Brussels sprouts contain noticeable amounts.
- Grains: Whole grains often contain RFOs.
Human Milk Oligosaccharides (HMOs)
In human biology, Human Milk Oligosaccharides (HMOs) are a highly abundant class of complex carbohydrates. They are the third most plentiful solid component in breast milk, with over 200 different structures identified. Unlike other oligosaccharides, HMOs primarily serve a beneficial prebiotic and immunomodulatory role for infants.
One specific HMO, 2'-Fucosyllactose (2'-FL), is the most abundant HMO and is produced by approximately 80% of lactating women worldwide. HMOs are not digested by the infant but act as a crucial food source for beneficial gut bacteria, particularly Bifidobacteria, helping to establish a healthy gut microbiome.
Galacto-oligosaccharides (GOS)
Galacto-oligosaccharides (GOS) are another prevalent type of oligosaccharide found in nature, most notably in mammalian milk and legumes. Similar to FOS, GOS also function as prebiotics by promoting the growth of Bifidobacteria and Lactobacilli in the colon. While naturally occurring in milk, commercial GOS is often produced enzymatically from lactose using β-galactosidase.
Isomalto-oligosaccharides (IMO)
Isomalto-oligosaccharides (IMO) are short chains of glucose oligomers typically produced commercially from starches like corn, wheat, or tapioca. While found naturally in some fermented foods and honey, their concentration is generally low. Due to their prebiotic effects and properties as a low-calorie sweetener, they are widely used in the food and beverage industry.
A Comparison of Abundant Oligosaccharides
| Oligosaccharide Type | Primary Natural Sources | Primary Monosaccharide Units | Key Characteristic(s) | Typical Abundance |
|---|---|---|---|---|
| Fructooligosaccharides (FOS) | Chicory root, onions, garlic, agave | Fructose (chains) | Well-studied prebiotic, low calorie sweetener | High (especially in chicory/yacón) |
| Raffinose Family (RFOs) | Legumes (beans, lentils), cabbage, broccoli | Galactose, Glucose, Fructose | Causes flatulence due to indigestibility by human enzymes | High in certain plant seeds/legumes |
| Human Milk (HMOs) | Human Breast Milk | Glucose, Galactose, Fucose, GlcNAc, Sialic acid | Crucial for infant gut health and immune support; highly complex | Third most abundant solid component in breast milk |
| Galacto-oligosaccharides (GOS) | Mammalian milk, legumes | Galactose (chains) | Prebiotic; commercial production from lactose | Present in milk and legumes; commercially produced |
| Isomalto-oligosaccharides (IMO) | Honey; commercially from starch | Glucose (chains) | Low-calorie sweetener, prebiotic | Low naturally; abundant commercially |
Conclusion: The Ubiquity and Importance of Oligosaccharides
From the foundational sustenance of infants provided by Human Milk Oligosaccharides to the prebiotic fiber in legumes and vegetables, oligosaccharides are a diverse and abundant class of carbohydrates with profound biological impacts. FOS and inulin derived from plants like chicory root, RFOs from legumes, and HMOs uniquely tailored for infants represent some of the most prevalent forms in our diet and biology. The abundance of these molecules, both natural and commercially produced, underscores their importance for gut health and overall nutrition across the life span. The increasing demand for functional foods continues to drive innovation in their production and application, highlighting their continued significance in nutrition science. The understanding of how these different abundant oligosaccharides function uniquely is key to leveraging their health benefits effectively.
For more in-depth information, the National Institutes of Health provides extensive research on oligosaccharides and their biological roles.
