Thermal degradation of betacyanins in juices from purple pitaya [Hylocereus polyrhizus (Weber) Britton & Rose] monitored by high-performance liquid chromatography-tandem mass spectometric analyses

Changes in betacyanin content and colour shade of juices from purple pitaya [Hylocereus polyrhizus (Weber) Britton & Rose] as affected by thermal processing and consecutive cold storage to allow pigment reconstitution were investigated. Pigments from purple pitaya displayed higher stability than earlier investigations on betalains suggested. A novel high-performance liquid chromatography method was established, allowing simultaneous detection of genuine pigments of purple pitaya juice together with their degradation products. In addition to previously described betanin cleavage products (betalamic acid, cyclo-dopa 5-O-beta-glucoside) further degradation products generated after decarboxylation and/or dehydration of phyllocactin and hylocerenin, respectively, were found. Moreover, neobetanin was identified as a thermal degradation product of betanin for the first time. With this newly developed high-performance liquid chromatography method, heating of purple pitaya juice and a commercial pitaya juice concentrate was proven by the detection of thermal betacyanin degradation products that had not been described, so far.