Saponins

With all this talk about natural emulsifiers and surfactants, I thought we'd get into a little chemistry about sapogenins and saponins! 

Saponins are steroid or triterpenoid glycosides that have amphiphilic or amphipathic features. They are grouped together by having "soap like foaming qualities they produce in aqueous solutions" - in other words, when you put them in water and shake them up, they foam. What the heck does this mean? Let's break it down...

Amphiphilic or amphipathic compounds are those that possess hydrophilic and lipophilic properties. Sound familiar? Yep, they're surfactants! They have one end that likes fat and another that likes water, so they can bring oils and water together to produce emulsification! Some of them also foam, which makes them like our lathery surfactants (Quillaja, soapwort, and Indian soapwort fall into this category).

Glycosides are molecules in which a sugar is bound to a non-carbohydrate moiety (functional group), usually a small organic molecule. The sugar group is known as a glycone and the non-sugar part is known as an aglycone or genin. If the glycone group is a glucose, then the resulting glycoside is known as a glucoside. If the glycone group is fructose, then the resulting glycoside is known as a fructoside.

One alcoholic glycoside we see a lot is salicin from the willow tree, which is converted into salicylic acid in our bodies. You can see the O-glucosyl part is the sugar part (the glycone) and the rest of the molecule is the aglycone.

The flavonoid glycosides are ones where the aglycone or non-sugar part is a flavonoid that behaves as an anti-inflammatory, anti-oxidant, and anti-microbial properties. Some of these include rutin and quercetin as the aglycone part.

So a saponin is a molecule to which a sugar is bound that can behave as a surfactant. It could be a foamy surfactant or an emulsifying surfactant, but it's something that can reduce the surface tension of water. We see it being used as an emulsifier in this Dr Bronner lotion (click here for the comment by p that started this mighty research journey) and we are seeing these saponins being used in a variety of natural cosmetics.

Most of these saponins dissolve easily in water and are poisonous to fish. There is a long history of fish-poisoning by saponins by indigenous tribes around the world. They are also known to kill protozoa and molluscs, impair digestion of protein and uptake of vitamin and minerals, cause hypoglycemia, and can behave as anti-fungals, anti-virals, and anti-oxidants. (Link here.)

An aside with a few of my thoughts: This could make for interesting preservatives, but it doesn't seem like anyone is using them in this fashion. As well, are these all natural surfactants any better than synthetically produced surfactants? If they're killing fish and molluscs, isn't this kind of defeating the purpose?

Join me tomorrow for more chemistry fun with saponins!