Total polyphenols were extracted as described by with minor modifications as follows. Aqueous-
organic extracts (extractable polyphenols) and their residues
(non-extractable polyphenols) were isolated and studied. In particular
in residues, among non-extractable polyphenols, hydrolysable
polyphenols (comprising hydrolysable tannins, phenolic acids and
hydroxycinnamic acids that are released from the food matrix by
strong acidic hydrolysis) were determined.