Where do galactooligosaccharides come from? An Overview of GOS Sources

November 15, 2025 •

4 min read

Galactooligosaccharides (GOS) are a class of prebiotic carbohydrates that are found naturally in milk, but are also commercially synthesized from lactose, a sugar present in dairy products. Their ability to resist digestion in the upper gastrointestinal tract allows them to reach the colon intact, where they selectively fuel beneficial bacteria like Bifidobacteria. This unique property has made understanding where do galactooligosaccharides come from increasingly important for the functional food industry.

Quick Summary

Galactooligosaccharides (GOS) originate from both natural food sources, like mammalian milk and legumes, and large-scale enzymatic synthesis using lactose from dairy by-products, such as whey.

Key Points

Natural Sources: Small amounts of galactooligosaccharides (GOS) are found naturally in certain foods, including mammalian milk (especially human and marsupial milk) and legumes like chickpeas and lentils.
Industrial Production: The majority of commercially available GOS is produced synthetically from dairy by-products, primarily lactose from whey.
Enzymatic Process: Industrial synthesis uses the enzyme β-galactosidase, or lactase, to convert lactose into GOS through a process called transgalactosylation.
Gut Health: As prebiotics, GOS resist digestion in the upper gut and selectively feed beneficial bacteria in the colon, such as Bifidobacterium and Lactobacillus.
Important Ingredient: Due to their gut health benefits, GOS are widely used as a functional ingredient in infant formulas, dairy products, and other supplements.
Varied Structures: The specific structure, chain length, and glycosidic linkages of GOS can vary depending on the enzyme source used in production.

The Dual Origin of Galactooligosaccharides

Galactooligosaccharides (GOS) have a dual origin, occurring naturally in certain foods but primarily being produced synthetically for commercial use. Their function as a prebiotic fiber—acting as food for beneficial gut bacteria—has driven significant interest in their sources and production. Understanding how they are derived is essential for both consumers seeking dietary sources and manufacturers incorporating them into functional foods.

Natural Sources of GOS

While commercially produced GOS dominates the market, smaller quantities can be found naturally in a variety of foods. These dietary sources provide GOS as a component of their overall nutritional profile.

Mammalian Milk: GOS occurs naturally in the milk of mammals, including humans, though the concentration varies. In human breast milk, they are one type of complex human milk oligosaccharides (HMOs). The concentration in cow's milk is typically lower, but still serves as a natural source.
Legumes: Certain legumes are known to contain α-GOS, which are slightly different in chemical structure from the β-GOS found in milk. Examples include lentils, chickpeas, and beans. These plant-based GOS variants are part of the raffinose family of oligosaccharides, known for their prebiotic effects.
Root Vegetables and Other Plants: Some other vegetables and plants also contain natural oligosaccharides, though not always identified specifically as galactooligosaccharides. Examples include asparagus, onions, and various grains.

Industrial Production of GOS from Dairy

For commercial applications, GOS is primarily produced synthetically, a process that relies heavily on the dairy industry. The enzymatic synthesis of GOS has become the standard method due to its efficiency and scalability.

The Enzymatic Synthesis Process

This process, known as transgalactosylation, uses a specific enzyme to convert lactose into GOS.

Sourcing the Lactose: The primary raw material is lactose, a disaccharide found in milk. It is often sourced as a by-product from the dairy industry, such as from whey or whey permeate.
Using β-galactosidase: The lactose is treated with the enzyme β-galactosidase, also known as lactase. This enzyme, sourced from microorganisms like Aspergillus oryzae, Kluyveromyces lactis, or Bacillus circulans, catalyzes the transfer of galactose units from lactose molecules to other sugars.
Transgalactosylation vs. Hydrolysis: In the reaction vessel, a balance is struck between transgalactosylation (building the GOS) and hydrolysis (breaking down lactose into glucose and galactose). To favor GOS production, high concentrations of lactose are used.
Reaction Completion and Purification: Once the desired GOS yield is reached, the process is stopped. The crude GOS mixture, which still contains residual lactose and monosaccharides, is then purified. Advanced purification methods, including chromatography and membrane filtration, help achieve high-purity GOS.

Comparison of GOS Production Methods


Feature	Natural Food Sources	Industrial Enzymatic Synthesis
Source Material	Mammalian milk, legumes, and plants.	Lactose from dairy by-products like whey.
Process	Bio-synthesis within the organism.	Enzymatic transgalactosylation using β-galactosidase.
Availability	Varies by food type and concentration; generally low.	Produced at large scale with high commercial availability.
GOS Concentration	Often low, mixed with other carbohydrates.	Can be concentrated and purified to high levels.
Consistency	Varies depending on factors like diet, season, and species.	Highly controlled, ensuring consistent product specifications.
Structures Produced	Naturally occurring structures, typically α- or β-linked depending on source.	Structures vary depending on the specific enzyme used.

GOS in the Gut and its Prebiotic Function

Regardless of their origin, GOS function as prebiotics because they are resistant to digestion by enzymes in the human stomach and small intestine. Upon reaching the large intestine, they are fermented by beneficial bacteria, primarily Bifidobacterium and Lactobacillus. This process produces short-chain fatty acids (SCFAs), which have numerous health benefits, including supporting gut barrier function and modulating immune responses. The specific structure and chain length of GOS can influence which bacteria are promoted and which SCFAs are produced, highlighting why the enzyme source in industrial production is important.

Conclusion: A Key Prebiotic with Diverse Origins

Galactooligosaccharides (GOS) originate from both natural food sources, like milk and legumes, and from an advanced industrial process that synthesizes them from lactose found in dairy. While natural foods offer small amounts of GOS, the majority used in supplements and functional foods is created through the controlled enzymatic transgalactosylation of lactose from dairy by-products. This synthetic approach ensures a consistent, high-purity supply for the growing market of gut health products. The dual origin of GOS—one ancient and one modern—reflects its established role as a powerful prebiotic ingredient in human nutrition.

Future Trends and Sustainable GOS Production

The dairy industry's by-products, like whey and lactose, are central to large-scale GOS manufacturing. As the demand for functional foods increases, there is a push towards more sustainable and efficient production methods. Researchers are exploring ways to increase GOS yield from existing dairy processing waste, minimizing both costs and environmental impact. Innovations in continuous production methods, such as enzyme membrane reactors, and selective microbial fermentation techniques are also being developed to create higher-purity GOS more efficiently. These advancements will further solidify GOS's position as a foundational prebiotic ingredient.

GOS vs. Human Milk Oligosaccharides (HMOs)

It is important to note that while GOS are used in infant formulas to mimic the prebiotic effects of human milk oligosaccharides (HMOs), they are not identical. HMOs are a more complex and diverse group of oligosaccharides. GOS are considered the closest available alternative for commercial formula, providing similar gut-supportive benefits. The similarity in function, particularly in promoting bifidobacteria, makes GOS a valuable additive.

Frequently Asked Questions

Yes, galactooligosaccharides (GOS) are found naturally in some foods, primarily mammalian milk and legumes like chickpeas and lentils, though typically in low concentrations.

The main commercial source is lactose derived from dairy by-products, especially whey. This lactose is converted into GOS through an enzymatic process.

They are produced using an enzymatic reaction called transgalactosylation, which uses the enzyme β-galactosidase to link galactose molecules from a lactose substrate.

While it is possible to get some GOS from dietary sources, the concentration is often low. For higher, therapeutic levels used in supplements or infant formulas, the synthetically produced version is necessary.

GOS from plants (legumes) often have a different chemical structure and linkages (alpha-linked) compared to the beta-linked GOS found in milk. Both act as prebiotics but may promote different bacteria.

No, GOS are not identical to HMOs. HMOs are a complex and diverse family of oligosaccharides found in breast milk. GOS are an effective, commercially available prebiotic often used in infant formula to mimic some of the prebiotic benefits of HMOs.

The specific enzyme used influences the final structure and chain length of the GOS. Different enzymes produce GOS with varying glycosidic linkages, which can affect their specific prebiotic properties and interaction with gut bacteria.