What Is Raffinose? The Complex Sugar in Your Food

Raffinose is a complex carbohydrate found throughout the plant kingdom. It is a naturally occurring sugar, classified as an oligosaccharide, present in a wide variety of vegetables, legumes, and grains. This sugar serves various functions within plants, including roles in stress response and seed viability. While abundant in nature, its journey through the human digestive system is distinct from that of simpler sugars.

The Chemical Makeup of Raffinose

Raffinose is a trisaccharide, which means it is constructed from three simple sugar units: galactose, glucose, and fructose. The chemical formula for raffinose is C18H32O16. The structure consists of a galactose unit linked to the glucose part of a sucrose molecule. Sucrose itself is a disaccharide made of glucose and fructose.

This structure places raffinose within a larger group of sugars known as the raffinose family of oligosaccharides (RFOs). These carbohydrates rank second only to sucrose in terms of abundance as soluble sugars in the plant world. Other members of this family include stachyose and verbascose, which contain four and five simple sugar units, respectively. The defining feature of this family is the addition of galactose units to a sucrose base.

Foods Containing Raffinose

A wide range of common plant-based foods contains raffinose. It is particularly concentrated in legumes, cruciferous vegetables, and various whole grains. Common sources include:

• Legumes like beans, chickpeas, and lentils
• Cruciferous vegetables such as cabbage, broccoli, and Brussels sprouts
• Other vegetables like asparagus and cauliflower
• Various whole grains

The presence of raffinose is a natural characteristic of these plants, where it plays a part in their biology, acting as a storage sugar or helping protect seeds from drying out. The amount of raffinose can vary between different foods and even within the same type of vegetable depending on its maturity and storage conditions.

How Humans Process Raffinose

The journey of raffinose through the human digestive system is determined by a specific enzymatic limitation. The human small intestine does not produce the enzyme alpha-galactosidase (α-GAL). This enzyme is required to break the bond linking the galactose unit to the raffinose molecule. Without this enzyme, the trisaccharide cannot be broken down into its simpler, absorbable sugar components.

Consequently, raffinose travels undigested through the stomach and small intestine. It arrives in the large intestine intact, where it encounters a different environment. The large intestine is home to a vast community of bacteria that possess the α-GAL enzyme and readily ferment the undigested raffinose for energy. This process distinguishes raffinose from other sugars like sucrose or glucose, which are digested and absorbed in the small intestine.

Effects of Raffinose Consumption

The fermentation of raffinose by gut bacteria produces gases, including hydrogen, methane, and carbon dioxide. The accumulation of these gases in the large intestine can cause digestive symptoms for some people after eating raffinose-rich foods. These symptoms commonly include flatulence, bloating, and abdominal discomfort.

The fermentation of raffinose also yields short-chain fatty acids (SCFAs), such as acetic, propionic, and butyric acids. These SCFAs can be absorbed by the body and have health benefits. Because raffinose serves as nourishment for certain gut microbes, it is considered a prebiotic. It promotes the growth of beneficial bacteria like lactobacilli and bifidobacteria, supporting the health of the gut microbiome.