Thearubigins

Thearubigins are high-molecular-weight polymeric polyphenol compounds formed through oxidative condensation of catechins during black tea fermentation. They are not a macronutrient or micronutrient source but rather a class of bioactive compounds. Molecular weight ranges broadly from 700 Da to over 40,000 Da, comprising a heterogeneous mixture of oxidized, polymerized catechin derivatives. Thearubigins account for approximately 60-70% of the total polyphenol content in brewed black tea by dry weight, with a typical brewed cup (200ml) containing approximately 100-200mg of thearubigins. They contribute negligible caloric value (effectively 0 kcal per serving). No protein, fat, or fiber content is inherent to thearubigins as isolated compounds. Key co-occurring bioactive compounds in their natural matrix include theaflavins (3-6% of black tea polyphenols), caffeine, and L-theanine. Bioavailability is notably limited and poorly characterized due to structural complexity and large molecular size; gut microbiota play a significant role in partial metabolism to lower-molecular-weight phenolic acids (e.g., gallic acid, protocatechuic acid) which are more readily absorbed in the colon. Oral bioavailability of intact thearubigin polymers is estimated to be low (<5%), with most systemic activity attributed to microbial metabolites. Iron absorption inhibition has been documented when consumed with meals due to polyphenol-iron chelation.