Structure-antioxidant activity relationships of flavonoids and phenolic acids

One of the most-cited papers in antioxidant chemistry — a foundational reference establishing why phenolic compounds are effective free radical scavengers. Published in Free Radical Biology and Medicine, this review by Rice-Evans and colleagues from King’s College London is the standard scientific reference for the structure-activity relationship of phenolic antioxidants.

The Core Finding

Free radical scavenging capacity in phenolic compounds is determined by the number, position, and configuration of hydroxyl (-OH) groups on aromatic rings. More hydroxyl groups, and their arrangement in specific positions relative to each other, produce stronger antioxidant activity. This explains why the diverse phenolic fraction in peat — which includes humic acids, free phenolic acids, and condensed tannins, all with multiple hydroxyl groups — produces measurable antioxidant activity in assays like ABTS and DPPH.

Why It’s Cited Here

Peat chemistry papers (including Tarnawski 2006, which measured peat phenolics directly) cite Rice-Evans 1996 to explain the mechanism behind measured antioxidant activity. The argument is: peat contains phenolic compounds → those phenolics have hydroxyl groups in antioxidant-active configurations → therefore peat shows free radical scavenging activity → therefore peat may protect skin cells from oxidative stress. Rice-Evans provides the middle link in that chain.

Grade Note

Grade A reflects the scientific authority of this paper, not clinical evidence. This is a chemistry and biochemistry reference explaining a mechanism, not a trial measuring outcomes in patients. It is cited as mechanistic support, not as proof that peat prevents skin aging in humans.