Continuous-Flow Ultrasound Processing Improves the Preservation of Thermolabile Metabolites and Betalains in Red Pitaya Pulp (Hylocereus polyrhizus)

Red pitaya (Hylocereus polyrhizus) is an important source of thermolabile bioactive compounds, particularly betalains, whose stability can be significantly affected during extraction processes. This study evaluated the influence of pressurized liquid extraction (PLE) and different ultrasound-assisted extraction (UAE) configurations on the recovery and preservation of bioactive compounds from red pitaya pulp, with special emphasis on thermal management during processing. Static UAE (UAE-1), ice-assisted UAE (UAE-2), and two continuous-flow ultrasound systems operating at 10 mL/min (UAE-3) and 20 mL/min (UAE-4) were compared with PLE under different processing conditions. Betalain content, total phenolic compounds, antioxidant activity assessed using ferric reducing antioxidant power (FRAP) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), thermal profiles, and metabolite composition determined by ultra-high-performance liquid chromatography–electrospray ionization–quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOF-MS) were evaluated. Continuous-flow ultrasound processing significantly improved the preservation of betalains and thermolabile metabolites compared with conventional extraction approaches. Among all treatments, UAE-3 (10 mL/min) showed the best overall performance, combining high betalain recovery, enhanced antioxidant activity, and a broad metabolite profile. A total of 39 metabolites were tentatively identified, including phenolic acids, flavonoids, coumarins, amino acids, alkaloids, fatty acids, and glycerophospholipids. The results demonstrate that controlling heat accumulation is more relevant than increasing extraction intensity alone when processing thermolabile compounds. These findings highlight the potential of continuous-flow ultrasound systems with effective thermal management as a strategy to produce bioactive-rich ingredients from red pitaya pulp. AGSA-Prep classified all five extraction workflows as Acceptably Green (61.1–62.5%), while GEARS yielded component scores of 67% for ethanol and 83% for water.