One green tea extract can legitimately be labelled “98% polyphenols” and “45% EGCG” at the same time - and those are not contradictory. Understanding why comes down to two different assay methods measuring two different things. This guide explains both so you can read a CoA correctly and write a defensible label.
Three Numbers, Two Methods
Green tea extract is described by three figures that are often confused:
| Figure | Method | What it measures | Typical range |
|---|---|---|---|
| Total polyphenols | UV-Vis (Folin-Ciocalteu) | All reducing polyphenols, broadly | 50-98% |
| Total catechins | HPLC | Sum of EGCG, EGC, ECG, EC | 40-80% |
| EGCG | HPLC | The single EGCG molecule | 30-50% |
Because each measures a progressively narrower set of compounds, the polyphenol number is always the largest and EGCG the smallest. A “98% polyphenols” claim says little about EGCG on its own.
How the UV Polyphenol Assay Works
The Folin-Ciocalteu method is a colourimetric reaction: polyphenols reduce a reagent, producing a blue colour whose intensity is read on a UV-Vis spectrophotometer and expressed against a gallic-acid (or catechin) standard. It is fast, inexpensive and reproducible, but non-specific - it responds to any reducing substance, so it reports a broad “polyphenol” total rather than the active catechins specifically.
How the HPLC Catechin/EGCG Assay Works
High-performance liquid chromatography physically separates the individual catechins on a reversed-phase (C18) column and quantifies each against authentic reference standards, with detection typically around 270-280 nm. This is what lets a CoA state a specific EGCG percentage, an EGC percentage and so on. HPLC is the method to insist on whenever your positioning, dose rationale or regulatory ceiling depends on EGCG.
Reading the Standardisation on a CoA
On a complete CoA you should see both an assay line for total polyphenols (UV) and separate HPLC lines for total catechins and EGCG. If only a UV polyphenol figure appears, you cannot verify the active catechin content from that document. Worked example of a high-grade batch:
| Parameter | Method | Result |
|---|---|---|
| Total polyphenols | UV | 91.6% |
| Total catechins | HPLC | 81.3% |
| EGCG | HPLC | 47.8% |
| Caffeine | HPLC | 6.2% |
Practical rule: Buy and label on the number your claim depends on. If the story is “rich in antioxidants”, a polyphenol spec may suffice; if it is “standardised EGCG” or tied to a clinical dose, specify EGCG by HPLC - and remember the EU 800 mg/day EGCG ceiling when you convert percentage to milligrams per serving.
To translate these specs into a purchase, see the buyer's guide; for what the catechins do, see the EGCG & catechin benefits review.
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