Degradation and metabolism of C-14-labelled proanthocyanidins from carob (Ceratonia siliqua) pods in the gastrointestinal tract of the rat

The aim of the work was to study the binding, degradation and metabolism of dietary condensed tannins in the gastrointestinal tract of an omnivore. Young pods of carob (Ceratonia siliqua L) were radiolabelled by in vivo feeding of (CO2)-C-14, trans-[U-C-14]cinnamate or L-[U-C-14]phenylalanine. [C-14]Proanthocyanidins (condensed tannins) were extracted with acetone/water (3:1 v/v), isolated on Sephadex LH-20 and fed to rats by gavage. After 4 and 18 h, 90-94% of the gavaged C-14 was in the gut contents and/or faeces. Much of the gavaged C-14 (57%), predominantly that originally in tannins of high degree of polymerisation (DP), became insolubilised, mainly in the form of protein-tannin complexes. Some of the [C-14]tannins that remained soluble decreased in DP, especially in the small intestine and caecum. A further fraction (12% of the C-14 gavaged) underwent chemical modifications in the gut to form soluble, non-tannin compounds. Small proportions of the C-14 were found in the liver (1.0-1.5%), urine (1-2%) and (CO2)-C-14 (1-2%). We conclude that proanthocyanidins are not inert within the gut but undergo various modifications which may affect the nutrition of the animal. (C) 2001 Society of Chemical Industry.