Flavanol–anthocyanin pigments in corn: NMR characterisation and presence in different purple corn varieties

A flavanol–anthocyanin condensed pigment was isolated from a commercial anthocyanin-rich purple corn powder and its structure elucidated by mass spectrometry and 1H and 13C NMR using 1D and 2D techniques (COSY, HSQC, HMBC). The compound was unequivocally identified as the dimer catechin-(4α→8)-cyanidin-3,5-O-diglucoside. In addition, six non-processed samples belonging to different corn varieties were analysed for their anthocyanin profiles, with the aim of checking if similar condensed pigments were present in native corn. The presence of condensed pigments was found in three corn varieties, whose identity was established from their UV and mass spectra and MS2 fragmentation patterns. The percentage of condensed pigments ranged between 0.3% and 3.2% of total anthocyanins. The whole of the observations made confirm that flavanol–anthocyanin condensed pigments can occur naturally in corn.