raffinose

Raffinose is a trisaccharide in the raffinose family oligosaccharides (RFOs). It consists of galactose bound to a sucrose moiety by a galactosyl α1→6 bond, i.e., galactosyl-(1→6)-sucrose. Its chemical formula is C18H32O16 and its molecular weight is about 504.5 g/mol. Raffinose is a non-reducing sugar, because all glycosidic linkages involve the anomeric carbons.

Natural occurrence and role: Raffinose occurs in seeds and vegetative tissues of many plants, especially legumes such as beans, lentils, and chickpeas, as well as in cereals, onions, and cabbage. It is part of the raffinose family oligosaccharides that accumulate under abiotic stress, where they are thought to help with osmotic protection and storage.

Biosynthesis: In plants, raffinose is synthesized from galactinol and sucrose by the enzyme raffinose synthase, transferring a galactosyl unit to the sucrose molecule to form raffinose. This places raffinose among stress-related oligosaccharides, alongside other members such as stachyose and verbascose that build on a galactinol core.

Digestive and health aspects: In humans, α-galactosidase activity is limited, so raffinose is not efficiently digested in the small intestine. It passes to the colon where gut bacteria ferment it, producing gas and other byproducts and contributing to flatulence in some individuals. Soaking, cooking, or fermentation can reduce raffinose content in foods, and some people tolerate it better when processed. Raffinose also has interest as a model carbohydrate in research on digestion and gut microbiota.