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.

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 composed of galactose and glucose and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from (Genitive case, gen. ), the Latin word for milk, plus the suffix ''-o ...

, 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 An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

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 structural unit, 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 polymeriza ...

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 take part in the chemical process of digestion, which follows the mechanical process of digestion. Food consists of macromolecules of proteins, carbohydrates, and fats that need to be broken down chemically by digestive enzymes ...

s. 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. 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.

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''. These sugars can be found naturally in human milk, 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 systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

. Galactooligosaccharides (GOS) support natural defenses of the human body via the gut microflora, indirectly by increasing the number of bacteria in the gut and inhibiting the binding or survival of ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

'', ''Salmonella'' ''typhimurium'' and ''

Clostridia The Clostridia are a highly polyphyletic class of Bacillota, including '' Clostridium'' and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them ...

''. GOS can positively influence the immune system indirectly through the production of antimicrobial substances, reducing the proliferation of pathogenic bacteria.

Constipation

Constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the ...

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

References