Galacto-oligosaccharides (GOS), also known as oligogalactosyllactose, oligogalactose, oligolactose or transgalacto-oligosaccharides (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.

In nature, trace amounts of organic galactooligosaccharides are present in the milk of animals, and the amount is slightly higher in breast milk. The Galactooligosaccharide sweetness is relatively pure and the caloric value is low (7.1 J/g).The sweetness is 20% to 40% of sucrose and the moisturizing property is extremely strong. It has high thermal stability under neutral pH conditions. After heating at 100 ° C for 1 h or at 120 ° C for 30 min, the galactooligosaccharides have no decomposition.Hence, it could be used for food such as bread, pastry processing.