Galactooligosaccharides (GOS), also known as oligogalactosyllactose, oligogalactose, oligolactose or transgalactooligosaccharides (TOS), belong to the group of

prebiotics Prebiotics are compounds in food that induce the growth or activity of beneficial microorganisms such as bacteria and fungi. The most common example is in the gastrointestinal tract, where prebiotics can alter the composition of organisms in the ...

. 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.

Chemistry

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 Lactose is a disaccharide sugar synthesized by galactose and glucose subunits and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from ' (gen. '), the Latin word for milk, plus the suffix '' - ...

, 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 Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

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 The degree of polymerization, or DP, is the number of monomeric units in a macromolecule or polymer or oligomer molecule. For a homopolymer, there is only one type of monomeric unit and the ''number-average'' degree of polymerization is given b ...

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 enzyme Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption into the cells of the body. Digestive enzymes are found in the digestive tracts of anim ...

s. Galactooligosaccharides are classified as

, defined as non-digestible food ingredients as substrate for the host by stimulating the growth and activity of bacteria in the colon. The increased activity of colonic bacteria results in various effects, both directly by the bacteria themselves or indirectly by producing

short-chain fatty acid Short-chain fatty acids (SCFAs) are fatty acids with fewer than six carbon atoms. Derived from intestinal microbial fermentation of indigestible foods, SCFAs are the main energy source of colonocytes, making them crucial to gastrointestinal healt ...

s as byproducts via fermentation. Examples of effects are stimulation of immune functions, absorption of

essential nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

s, and synthesis of certain vitamins.

Stimulating bacteria

Galactooligosaccharides are a substrate for bacteria, such as ''

Bifidobacteria ''Bifidobacterium'' is a genus of gram-positive, nonmotile, often branched anaerobic bacteria. They are ubiquitous inhabitants of the gastrointestinal tract though strains have been isolated from the vagina and mouth ('' B. dentium'') of mamma ...

'' and

lactobacilli The ''Lactobacillaceae'' are a family of lactic acid bacteria. It is the only family in the lactic acid bacteria which includes homofermentative and heterofermentative organisms; in the ''Lactobacillaceae,'' the pathway used for hexose fermentati ...

. Studies with infants and adults have shown that foods or drinks enriched with galactooligosaccharides result in a significant increase in ''Bifidobacteria''. These sugars can be found naturally in

human milk Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by mammary glands located in the breast of a human female. Breast milk is the primary source of nutrition for newborns, containing fat, protein, carbohydrates (lacto ...

, known as human milk oligosaccharides. Examples include lacto-''N''-tetraose, lacto-''N''-neotetraose, and lacto-''N''-fucopentaose.

Immune response

Human gut microbiota play a key role in the intestinal

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

. Galactooligosaccharides (GOS) support natural defenses of the human body via the

gut microflora Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut mi ...

, indirectly by increasing the number of bacteria in the gut and inhibiting the binding or survival of ''Escherichia coli'', ''Salmonella'' ''typhimurium'' and ''Clostridia''. GOS can positively influence the immune system indirectly through the production of antimicrobial substances, reducing the proliferation of pathogenic bacteria.

Constipation

Constipation is a potential problem, particularly among infants, elderly and

pregnant women Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

. In infants, formula feeding may be associated with constipation and hard stools. Galactooligosaccharides may improve stool frequency and relieve symptoms related to constipation.

References