Raffinose is a trisaccharide oligosaccharide composed of three monosaccharide units: galactose, glucose, and fructose. Structurally, it is an α-galactosyl derivative of sucrose, where a galactose unit is attached to the glucose moiety of sucrose via an α-1,6-galactosidic linkage. Raffinose belongs to the raffinose family oligosaccharides (RFOs), which also includes larger oligosaccharides such as stachyose and verbascose, commonly found in a wide variety of plant seeds and legumes.

Biological Role in Plants

Functionally, raffinose serves as a carbohydrate reserve in plants and plays an important role in stress tolerance by stabilizing cell membranes and proteins during conditions such as drought or desiccation. It is synthesized in specialized companion cells of plant minor veins, where raffinose synthase catalyzes the formation of raffinose from sucrose and galactinol.

Digestion and Fermentation in Humans

In human and monogastric animal digestion, raffinose is indigestible because they lack the enzyme α-galactosidase. Instead, raffinose is fermented by gut bacteria in the large intestine, producing short-chain fatty acids and gases. This fermentation contributes to the flatulence associated with the consumption of beans and other legumes.

Impact on Nutrition and Human Health

Beyond its physiological roles in plants, raffinose affects human nutrition and gut microbiota composition. It is one of the major soluble sugars in legumes such as chickpeas and soybeans. Research increasingly focuses on modifying raffinose content in crops to balance its nutritional benefits while reducing antinutritional effects. Due to its chemical stability and interaction with biological membranes, raffinose remains significant for both plant physiology and dietary considerations.