Contents of total polyphenols, condensed tannins and proanthocyanidins, and their stability to various pH values and temperatures were studied in Mexican blueberry, cuautecomate fruit, garambullo fruit, aubergine, coffee pulp and residues of black grapes. Several aqueous extracts, obtained through a one-pass-extraction process, were analyzed using liquid chromatography in order to quantify the condensed tannin (proanthocyanidin) content responsible for their antioxidant activity and colour. All tested samples included high proanthocyanidin contents demonstrating that these Mexican fruits and vegetables are good sources of natural antioxidants, and they all could be considered as excellent functional foods due to their bioactivity measured as the condensed tannin level.