Tannic acid is a conjugate of glucose and gallic acid residues. Long-term ingestion of large quantities of certain tannin-containing plant materials may be carcinogenic and these tannin-binding proteins could be a defence against this.
The high concentration of tannin-binding proteins in human saliva may be related to the diet of human ancestors. Tannin formulations can contain glucose in addition to gallic acid. Gallic acid, a main component in hydrolysable tannins, was mentioned above. They are part of the plant's defences against environmental stress.
Condensed tannins are polyphenols, widespread in plants.
