The cacao bean as a polyphenol source
Raw fermented cacao contains between 60 and 80 mg of polyphenols per gram of dry weight — one of the highest concentrations recorded in any food. These compounds belong to the flavanol (flavan-3-ol) subgroup of flavonoids. The three most abundant are epicatechin, catechin, and procyanidins.
Epicatechin and catechin: epimers at ring C
Both molecules share molecular formula C₁₅H₁₄O₆ and are epimers: same atomic connectivity but differing in the spatial configuration of a single stereogenic carbon — C-3 of the C ring.
| Property | (−)-Epicatechin | (+)-Catechin | |---|---|---| | C-3 configuration | 2R, 3R | 2R, 3S | | Optical rotation | −34° | +16° | | Abundance in cacao | 35–40% | 10–15% | | Thermal stability | Epimerizes to catechin on heating | More stable |
The epimerization of epicatechin to catechin during roasting explains why more heavily roasted chocolates have greater catechin content and a more astringent character. Above 130 °C, the C-3 inversion is progressive and irreversible.
Antioxidant activity by structure
The antioxidant capacity of flavanols derives from three structural features visible in the 3D model: the catechol group on ring B (two adjacent –OH groups optimal for radical capture), the free –OH at C-3 (participates in metal chelation of Fe²⁺ and Cu²⁺), and the –OH groups on ring A at positions 5 and 7.
Procyanidins: when monomers polymerize
Cacao procyanidins are epicatechin polymers linked through C4→C8 bonds (type B). Raw Criollo cacao from Colombia can contain procyanidin B2 (the epicatechin–(4β→8)–epicatechin dimer) at up to 18% of total flavanols.
Fermentation and polyphenol loss
The central paradox: fermentation is essential for flavor, but destroys most polyphenols. During 5–7 days of fermentation, polyphenol oxidase (PPO) oxidizes epicatechin to brown quinones — responsible for the brown color of the fermented bean. An estimated 60–80% of initial epicatechin content is lost during standard fermentation.
This trade-off between flavor precursor development and polyphenol preservation is at the heart of current research in cacao processing optimization.
The next article enters fermentation proper: the organic acids of cacao — acetic, lactic, and succinic — and how the microbial dynamics of the first five days determine the final acidity of chocolate.