What are saponins?
Saponins are a secondary plant metabolite class known as amphipathic glycosides, with diverse biological application found in various plant species. Amphipathic means that these compounds are both hydrophilic and hydrophobic. Specifically, a saponin compound is moiety made of a hydrophilic glycoside and hydrophobic sapogenins (or aglycone). When mixed into a aqueous solution, amphipathic glycosides exhibit surfactant properties due to the water soluble glycoside and fat soluble sapogenin. This gives saponins their foaming quality. Their properties as a surfactant make this compound a viable natural emulsifier.
Why we use these compounds?
Due to the surfactant properties that within saponins, and the fact that saponins are a product of plants, it is a perfect solution for organic farming emulsification. A large challenge with organic farming practice seems to be that some of the most important constituents within plants that are found useful in the agriculture industry are typically in a oil form after being extracted from the plant. There are other methods of plant extractions that are also very effective but in some cases the oils are most available as well as most concentrated forms of the desired phytochemicals. This is were an organic emulsification methods becomes a missing link in organic farming strategy. As a emulsifier, a plant source with high saponin content will emulsify oil with water, and help make natural and effective plant feed or IPM.
How to use this in organic agriculture?
The plant ‘Sapindus mukorossi’ is more commonly known as the Ritha or soap nut tree. We frequently work with extracts from this plant specifically because of its very high saponin content. There is about 10% saponins in the fruit pulp of the Soap nut, which is usually what one would receive after ordering soap nuts. The fruit is de-seeded and the remaining pulp is used in various possible extraction methods, and for the sake of simplicity and staying as natural as possible water has been our selection. Coincidentally with the information known on extraction methods for soap nuts seems to be indicate water is the best solvent to use for extraction of saponins (75.6% at a 1:10 solid to liquid mixture), only slightly more saponin content was extracted with a water and ethanol mixture (78.1% at a 1:10 solid to liquid ratio). A diversity of IPM mixtures can be made for various plant predators or pathogens, utilizing the emulsification properties of the soap nut. Besides the already proven insecticidal properties of saponins, the potential combinations of other phytochemicals in the forms of oils that are not readily soluble in water become possible, broadening the spectrum of plant stimuli possible through natural means. For example, neem oil is a renowned insecticide amongst other things, but to spray it foliarly it needs to be mixed with a aqueous solution. To solve this problem effectively and naturally, a combination of soap nut extract, neem oil, and water can be blended together to create a homogenous mixture of the three constituents that is capable of being sprayed onto the plants with uniformity. No separation of the lipid and water molecules. The oils are suspended throughout the aqueous solution via surfactant properties of the saponins, opening a vast realm of exploration and eventual manipulation of plant responses.
We have developed several successful IPM strategies around this concept, as well as fungicide applications. When an objective is to be met, nature provides all the constituents necessary to meet the need, and subsequently a multitude of benefits that are inherent when working in concert with natural compounds. Benefits that typically are not of primary concern, but beneficial non the less.