Shatavari, tribulus and the saponin assay problem

Saponin percentages are the softest numbers in the botanical extract trade. The gravimetric and colourimetric methods behind most of them will happily count material that has nothing to do with the herb.

Why saponin assays are weak

Saponins are a structurally diverse class, so there is no single compound to measure. The common approaches are:

• Gravimetric — extract with a solvent, dry, weigh what is left. It measures a solvent fraction, not a compound class. Anything that partitions the same way is counted.
• Colourimetric (vanillin-sulphuric acid and variants) — measures a colour reaction that many non-saponin compounds also give.

Both are cheap and fast, and both can be inflated by adding almost any suitable bulk material. This is well known within the trade, and it is why a saponin figure alone should never be the basis of a purchase.

What to specify instead

Wherever the plant has a defined marker, specify that marker by HPLC:

• Tribulus terrestris — protodioscin by HPLC, rather than "40% saponins". Protodioscin content varies enormously with the geographic origin and plant part, and it is the parameter that genuinely differentiates the material.
• Shatavari (Asparagus racemosus) — shatavarin IV by HPLC. Also confirm the plant part: root is the traditional material, and aerial parts are a cheaper substitution.
• Fenugreek — furostanol saponins or a named marker by HPLC.

Where no validated marker method exists, a chromatographic fingerprint compared to a retained reference batch is the next best control, and it is far harder to defeat than a colourimetric total.

The parameters that go with it

• Plant part and species, confirmed by HPTLC or DNA where substitution risk is real.
• Extract ratio and carrier, both declared.
• Extraction solvent with residual solvent limits.
• Heavy metals, pesticides, aflatoxins and microbiology — the standard botanical set.

A practical safeguard

Ask for a retained reference sample from the batch you approve, and keep it. Fingerprinting a future delivery against a physical reference you hold is the most effective adulteration check available to a buyer, and it costs almost nothing to set up at the start of a relationship.