Rhizobian gum

The discovery of Rhizobian gum comes from agronomical research and the study of microorganisms living in the soil in symbiosis with plants. A specific microorganism identified as a Rhizobium bacterium lives in contact with the roots of sunflowers. Hosted by the roots, this symbiotic bacterium is gram-negative, catalase-negative, and oxidase-positive. At the time of drought, the polymer synthesized by the bacterium forms a film around the root. Rhizobian gum stocks water present in small amounts in the soil making it available for absorption by roots, allowing the allows the plant to survive despite extreme climatic conditions. The biopolymer has also an important role in maintaining the soil structure.

As Rhizobian gum plays the role of a natural water exchanger with an extraordinary moisture-binding ability, it has interesting properties for cosmetic applications. Chemically Rhizobian gum is a branched polymer where repeating triplets of glucose and galactose polysaccharide units alternate with glucuronic acid,  pyruvate group, and acetyl groups.

During fermentation, the Rhizobium bacterium consumes glucose in solution and produces Rhizobian gum. The yield of conversion of glucose into Rhizobian gum is about 50%. In its native form, it shows the characteristics of a viscous polysaccharide, after the heat treatment, the polysaccharide acquires gel properties. The melting point of Rhizobian gum is close to 60°C, but it gets lower after sterilization. It can be close to body temperature. Depending on temperature and concentration, the gel can shift between dissociated flexible chains and partially organized chains with junction zones. The last conformation has a higher affinity toward the water.

Rhizobian Gum improves the sensory properties of cosmetic formulations. It enhances the brightness of emulsions and leaves a moisturizing, silky film on the skin. Thanks to the particular properties of its gel, it has an outstanding self-cooling property. It is caused by the evaporation of water released during application. This can be used to formulate mild cooling formulations, such as eye contour serums. The efficacy of the Rhizobian gum patches against dark circles has been proved by clinical tests.