Galactooligosaccharides (GOS), also known as oligogalactosyllactose, oligogalactose, oligolactose or transgalactooligosaccharides (TOS), belong to the group of prebiotics. Prebiotics are defined as non-digestible food ingredients that beneficially affect the host by stimulating the growth and/or activity of beneficial bacteria in the colon. GOS occurs in commercially available products such as food for both infants and adults.

Molar mass Variable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The composition of the galactooligosaccharide fraction varies in chain length and type of linkage between the monomer units. Galactooligosaccharides are produced through the enzymatic conversion of lactose, a component of bovine milk.

A range of factors come into play when determining the yield, style, and type of GOS produced. These factors include:

  • enzyme source
  • enzyme dosage
  • feeding stock (lactose) concentration
  • origins of the lactose
  • process involved (e.g. free or immobilized enzyme)
  • reaction conditions impacting the processing situation
  • medium composition

GOS generally comprise a chain of galactose units that arise through consecutive transgalactosylation reactions, with a terminal glucose unit. However, where a terminal galactose unit is indicated, hydrolysis of GOS formed at an earlier stage in the process has occurred. The degree of polymerization of GOS can vary quite markedly, ranging from 2 to 8 monomeric units, depending mainly on the type of the enzyme used and the conversion degree of lactose.

Digestion research

Because of the configuration of their glycosidic bonds, galactooligosaccharides largely resist hydrolysis by salivary and intestinal digestive enzymes.[1] Galactooligosaccharides are classified as prebiotics, defined as non-digestible food ingredients as substrate for the host by stimulating the growth and activity of bacteria in the colon.[1]

The increased activity of colonic bacteria results in various effects, both directly by the bacteria themselves or indirectly by producing short-chain fatty acids as byproducts via fermentation. Examples of effects are stimulation of immune functions, absorption of essential nutrients, and synthesis of certain vitamins.[2][3][4]

Stimulating bacteria

Galactooligosaccharides are a substrate for bacteria, such as Bifidobacteria and lactobacilli. Studies with infants and adults have shown that foods or drinks enriched with galactooligosaccharides result in a significant increase in Bifidobacteria.[1] These sugars can be found naturally in human milk, known as human milk oligosaccharides.[5] Examples include lacto-N-tetraose, lacto-N-neotetraose, and lacto-N-fucopentaose.[6]

Immune response

Human gut microbiota play a key role in the intestinal immune system.[1] Galactooligosaccharides (GOS) support natural defenses of the human body via the gut microflora,[7] indirectly by increasing the number of bacteria in the gut and inhibiting the binding or survival of Escherichia coli, Salmonella typhimurium and Clostridia.[8][9] GOS can positively influence the immune system indirectly through the production of antimicrobial substances, reducing the proliferation of pathogenic bacteria.[10][11]


Constipation is a potential problem, particularly among infants, elderly and pregnant women. In infants, formula feeding may be associated with constipation and hard stools.[12] Galactooligosaccharides may improve stool frequency and relieve symptoms related to constipation.[13]

See also

  • Xylooligosaccharide (XOS)


  1. Jeurink, P. V; Van Esch, B. C; Rijnierse, A; Garssen, J; Knippels, LM (2013). "Mechanisms underlying immune effects of dietary oligosaccharides". American Journal of Clinical Nutrition. 98 (2): 572S–7S. doi:10.3945/ajcn.112.038596. PMID 23824724.
  2. Gibson GR (October 1998). "Dietary modulation of the human gut microflora using prebiotics". British Journal of Nutrition. 80 (4): S209–12. doi:10.1017/S0007114500006048. PMID 9924286.
  3. Roberfroid MB (June 2000). "Prebiotics and probiotics: are they functional foods?". American Journal of Clinical Nutrition. 71 (6 Suppl): 1682S–7S, discussion 1688S–90S. doi:10.1093/ajcn/71.6.1682S. PMID 10837317.
  4. Macfarlane GT, Steed H, Macfarlane S (February 2008). "Bacterial metabolism and health-related effects of galacto-oligosaccharides and other prebiotics". Journal of Applied Microbiology. 104 (2): 305–44. doi:10.1111/j.1365-2672.2007.03520.x. PMID 18215222. S2CID 205319925.
  5. "Human Milk Oligosaccharides". NNI Global Website. Retrieved 2020-12-04.
  6. Miesfeld, Roger L. (July 2017). Biochemistry. McEvoy, Megan M. (First ed.). New York, NY. ISBN 978-0-393-61402-2. OCLC 952277065.
  7. Gibson G.R.; McCartney A.L.; Rastall R.A. (2005). "Prebiotics and resistance to gastrointestinal infections". Br. J. Nutr. 93 (Suppl. 1): 31–34. doi:10.1079/BJN20041343. PMID 15877892.
  8. Shoaf K.; Muvey G.L.; Armstrong G.D.; Hutkins R.W. (2006). "Prebiotic galactooligosaccharides reduce adherence of enteropathogenic Escherichia coli to tissue culture cells". Infect Immun. 74 (12): 6920–8. doi:10.1128/iai.01030-06. PMC 1698067. PMID 16982832.
  9. Sinclair HR, et al. (2009). "Galactooligosaccharides (GOS) inhibit Vibrio cholerae toxin binding to its GM1 receptor". Journal of Agricultural and Food Chemistry. 57 (8): 3113–3119. doi:10.1021/jf8034786. PMID 19290638.
  10. Macfarlane GT, Steed H, et al. (2008). "Bacterial metabolism and health-related effects of galacto-oligosaccharides and other prebiotics". Journal of Applied Microbiology. 104 (2): 305–344. doi:10.1111/j.1365-2672.2007.03520.x. PMID 18215222. S2CID 205319925.
  11. Vos AP, M'Rabet L, et al. (2007). "Immune-modulatory effects and potential working mechanisms of orally applied nondigestible carbohydrates". Critical Reviews in Immunology. 27 (2): 97–140. doi:10.1615/critrevimmunol.v27.i2.10. PMID 17725499.
  12. Scholtens, P. A; Goossens, D. A; Staiano, A (2014). "Stool characteristics of infants receiving short-chain galacto-oligosaccharides and long-chain fructo-oligosaccharides: A review". World Journal of Gastroenterology. 20 (37): 13446–13452. doi:10.3748/wjg.v20.i37.13446. PMC 4188896. PMID 25309075.
  13. Yu, T; Zheng, Y. P; Tan, J. C; Xiong, W. J; Wang, Y; Lin, L (2017). "Effects of Prebiotics and Synbiotics on Functional Constipation". The American Journal of the Medical Sciences. 353 (3): 282–292. doi:10.1016/j.amjms.2016.09.014. PMID 28262216.
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