Why Antioxidant Measurement Exists
Reactive oxygen species (ROS) — free radicals produced during normal metabolism and by environmental exposures — are implicated in cellular damage linked to ageing and disease. Compounds that quench these radicals are "antioxidants." The body has its own enzymatic antioxidant systems (superoxide dismutase, catalase, glutathione peroxidase), but dietary antioxidants were hypothesised to supplement these.
The challenge for researchers has been measuring how effectively a food or compound handles these radicals. Different assays were developed to measure different radical types and different antioxidant mechanisms. Tea, with its extraordinary polyphenol content, consistently scores very high on all of them.
| Assay | Radical/System Measured | Mechanism | Units | Limitation |
|---|---|---|---|---|
| ORAC | Peroxyl radical (ROO•) | Hydrogen atom transfer (HAT) | µmol Trolox Equivalents/g | Discontinued by USDA; poor human correlation |
| FRAP | Ferric iron (Fe³⁺) | Single electron transfer (SET) | mmol Fe²⁺/L or g | Misses HAT antioxidants, pH sensitive |
| DPPH | DPPH• radical (stable) | HAT and SET | µmol Trolox Equivalents/g | Lipid phase, not representative of aqueous biology |
| ABTS/TEAC | ABTS•+ radical cation | Electron transfer | mmol Trolox Equivalents/g | Can overestimate uric acid contribution |
| CERAC | Reactive oxygen species mix | HAT | µmol Trolox Equivalents/g | Newer, better correlated but complex |
Why the USDA Removed ORAC Scores
From 1992 to 2012, the USDA maintained an ORAC database listing the "antioxidant capacity" of thousands of foods. Tea, matcha, and herbal infusions featured prominently with very high scores, generating enormous marketing copy. In 2012, the USDA withdrew the database with an explicit statement:
"ORAC values are routinely misused by food and dietary supplement manufacturing companies to promote their products and by consumers to guide their food and supplement choices... there is no evidence that the beneficial effects of polyphenol-rich foods can be attributed to their antioxidant properties."
This was not a statement that tea antioxidants are ineffective — but that the ORAC number does not capture the relevant biology. Polyphenol compounds may exert their effects through mechanisms entirely different from radical scavenging, including modulation of gene expression, enzyme inhibition, and gut microbiome interaction.
🧠 Expert Tip: Marketing Scepticism
Any health claim on tea packaging that references ORAC scores should be treated with caution. The compound to compound correlation between ORAC and human health outcome is poor. A better question to ask is: what clinical trials in humans, at realistic doses, show health benefits from this type of tea?
What High In Vitro Antioxidant Scores Do Tell Us
While ORAC, FRAP, and DPPH do not directly predict human health effects, they are useful for: (1) Comparing similar compounds within a class (e.g., which catechin is the most potent radical scavenger in vitro); (2) Quality control — ensuring polyphenol content is consistent across batches; (3) Screening candidate compounds for health research — high in vitro scores justify further in vivo investigation.
Realistic Antioxidant Comparison
| Tea Type (brewed, standard) | Approx. FRAP (mmol/g) | Approx. DPPH EC50 | Approx. EGCG per cup |
|---|---|---|---|
| Matcha (1g powder/80ml) | Very high | Very low (very effective) | 100–200mg |
| Gyokuro (3g/150ml) | High | Low (very effective) | 80–150mg |
| Sencha (3g/200ml) | High | Low | 60–120mg |
| Darjeeling 1st flush | Moderate-high | Low-moderate | 40–80mg |
| Assam CTC black tea | Moderate | Moderate | 20–50mg (theaflavins replace EGCG) |
| White tea (Silver Needle) | Moderate-high | Low-moderate | 50–100mg |
The practical takeaway: all teas have meaningful polyphenol content by any in vitro measure. Matcha and gyokuro score highest due to their suspended whole-leaf or shade-concentrated chemistry. But the difference between a well-prepared sencha and matcha — when adjusted for normal serving concentrations — is smaller than the marketing suggests. All categories of tea contribute meaningfully to dietary polyphenol intake.
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