Studies on betalains chemistry from the Vietnamese red dragon fruits (Hylocereus polyrhizus) by LC-ESI-MS/MS

Abstract

The principle pigments from Vietnamese red dragon fruits (Hylocereus polyrhizus) were investigated qualitatively the first time by liquid chromatography connected to tandem mass spectrometry approach (LC-ESI-MS/MS). Both betacyanins and betaxanthins were detected from the crude and purified extracts based on the maximum UV absorbance of 540 nm and 480 nm, together with the daughter ions at m/z 389 and 265, respectively. The main betacyanins were identified as betanin/isobetanin ([M+H]+ at m/z 551), phyllocactin/isophyllocactin (6’-O-malonylbetanin, [M+H]+ at m/z 637) and apiosyl-betanin/apiosyl-isobetanin ([M+H]+ at m/z 683) next to the minor derivative of hylocerenin/isohylocerenin ([M+H]+ at m/z  695), 2’-apiosyl-phyllocactin/2’-apiosyl-isophyllocactin ([M+H]+ at m/z 769)  and traces of betanidin 5-O-β-sophoroside/isobetanidin 5-O-β-sophoroside ([M+H]+ at m/z 713). The primary yellow indicaxanthin was also recognized at m/z 309. These compounds appear in different ratios in comparison to other Hylocereus polyrhizus cultivar reported before. Their degradation products of decarboxylation and dehydrogenation namely decarboxy-betanin ([M+H]+ at m/z 507) and neobetanin ([M+H]+ at m/z 549) were also found in traces. These artifacts were not found in the fresh fruits and were suspected to be generated through harvesting and processing conditions of high temperature and sunlight.