What are the bioactive compounds of the duckweed?

The Spirodela polyrhiza is a perennial aquatic plant belonging to the Araceae family. It typically grows in dense colonies that form a mat-like layer on the water's surface. Each plant resembles a smooth, round, and flat disc measuring 0.5 to 1 cm wide with a green surface. The spirodela thrives in ponds and slow-moving bodies of water and rarely blooms. Initially valued for its nutritional properties, the water lentil is now sought after for its cosmetic benefits, particularly its hydrating properties appreciated by dehydrated skin. The various virtues of the spirodela come from the unique composition of its cell wall, particularly rich in apiogalacturonans, specialized pectins.

The spirodela used in skincare is composed of approximately 60% apiogalacturonans.

The role of apiogalacturonanes is to ensure the water exchanges of the duckweed as well as to provide great plasticity to the plant during its multiplication. In their native form, the apiogalacturonanes of the Spirodela polyrhiza present a linear structure composed of a linear chain of galacturonic acids formed by strong bonds and branches of di-apioses motifs linked by weak bonds. Apiogalacturonanes are hygroscopic molecules, meaning they are capable of attracting and retaining water, and are largely responsible for the moisturizing properties of the duckweed.

The cell wall of the Spirodela polyrhiza also contains rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II), with RG-II being highly cross-linked. Xylogalacturonan is also present, but in lesser abundance. Xylan, xyloglucan, and glucomannan are also part of the spirodela's cell wall, but these hemicelluloses are present in smaller quantities than the previously mentioned pectins. Finally, this plant is naturally low in lignin, which contributes to its digestibility and its suitability for biofuel production.

Flavonoids are also found in the spirodela. In addition to their hygroscopic properties, flavonoids are known for their aromatic structure, which gives them antioxidant power. By neutralizing the free radicals, they can prevent damage caused by oxidative stress to cell membranes and preserve the integrity of skin tissues. The Spirodela polyrhiza when applied topically is associated with antioxidant virtues, partly due to the flavonoids it contains. This plant also contains other metabolites, such as chlorophylls, anthocyanins, γ-aminobutyric acid, dopamine, threonine, valine, and phytosterols. The latter are associated with anti-inflammatory properties, also held by the spirodela. Some studies conducted on mice have shown that this plant could help in cases of atopic eczema, an inflammatory dermatosis.