- Stachyose is a naturally occurring tetrasaccharide with the molecular formula C₂₄H₄₂O₂₁. It belongs to the family of raffinose-series oligosaccharides (RFOs) and is composed of one galactose unit linked to raffinose, which itself consists of galactose, glucose, and fructose. Thus, the full structure of stachyose can be described as galactose–galactose–glucose–fructose. Like other RFOs, stachyose is non-reducing and water-soluble, and it is widely distributed in the plant kingdom, especially in legumes, certain vegetables, and tubers.
- In plants, stachyose serves as an important transport and storage carbohydrate. Many higher plants use raffinose-family oligosaccharides, including stachyose, as transport sugars in the phloem instead of sucrose. This adaptation is thought to enhance stress tolerance, since RFOs can protect cellular structures under conditions such as desiccation, cold, and oxidative stress. Stachyose, along with raffinose and verbascose, contributes to osmoprotection and may play roles in seed desiccation tolerance, germination, and longevity.
- From a nutritional perspective, stachyose has both beneficial and undesirable properties. In humans and many animals, it is not digested in the small intestine, because humans lack the enzyme α-galactosidase required to hydrolyze the galactosidic linkages. Instead, it passes into the large intestine where it undergoes fermentation by gut microbiota, producing gases such as hydrogen, methane, and carbon dioxide. This explains why stachyose, along with raffinose, is associated with flatulence and gastrointestinal discomfort when consuming beans, soy, and other legumes. However, this same property also gives stachyose prebiotic potential, as it can promote the growth of beneficial bacteria such as Bifidobacteria and Lactobacilli, contributing to improved gut health.
- Industrially and medically, stachyose and related RFOs have gained interest as functional food ingredients. Their prebiotic effects are being investigated for roles in modulating the gut microbiome, improving mineral absorption, and enhancing immune responses. Moreover, stachyose-containing extracts from plants such as soybeans have been studied for potential antioxidant and anti-inflammatory activities. Enzymatic treatment of food products with α-galactosidase is often employed to reduce stachyose and raffinose content, improving digestibility while preserving nutritional benefits.
