Betacyanins in fruits from red-purple pitaya, Hylocereus polyrhizus (Weber) Britton & Rose

The betalain pattern of Hylocereus polyrhizus (Weber) Britton & Rose is reported for the first time and a highly practicable technique is described for the simultaneous isolation of pigment and mucilage from the mesocarp by extraction with water. Whereas betaxanthins were totally absent, 10 betacyanins could be separated by HPLC-PDA. For eight betacyanins the respective molecular masses could be obtained by positive ion electrospray mass spectrometry. Five of them were unequivocally assigned to bougainvillein-r-I, betanin, isobetanin, phyllocactin, and iso-phyllocactin. The remaining betacyanins were tentatively identified as (6′-O-3-hydroxy-3-methyl-glutaryl)-betanin, its C15-stereoisomer, and (6′-O-3-hydroxy-3–butyryl)-betanin, respectively. Using the β-glucosidase assay, acylated structures could be distinguished from non-acylated betacyanins. Contrary to white-fleshed Hylocereus undatus (Haworth) Britton & Rose with a slightly pink mesocarp, H. polyrhizus most likely possesses the same set of betalain forming enzymes in both pulp and mesocarp as the betacyanin pattern was found to be similar.