Evaluation of green extraction methods on bioactive compounds and antioxidant capacity from Bougainvillea glabra bracts

Abstract Bougainvillea glabra is a native plant of South America, and its bracts are still an underexploited source of betalains and phenolic compounds. Microwave (MAE), ultrasound (UAE), conventional aqueous and ethanolic exhaustive extractions were used for the recovery of total phenolic compounds (TPC) and betalains from B. glabra bracts. The highest yields of TPC, betalains, and antioxidant capacity by ABTS were obtained by ethanolic exhaustive extraction followed by MAE at 100 and 600 W. Deoxyribose protection assay measurement by hydroxyl radical scavenging showed high values for extracts obtained by exhaustive extraction and MAE, ranging from 89% to 83%, indicating a high capacity to capture hydroxyl radicals. Agarose gel electrophoresis assay showed that the extracts obtained by UAE, conventional aqueous, and ethanolic extraction were able to protect DNA from free radicals and did not show pro-oxidant effect. Seventeen phenolic compounds and seventeen betalains were identified by HPLC/MS in the extract of B. glabra bracts obtained by exhaustive extraction, composed mainly of kaempferol derivatives (76.5%) and acylated betalains (71.0%), respectively. The results suggest that MAE may be an alternative to recover betalains and phenolic compounds from B. glabra bracts due to the lower extraction times and the absence of organic solvent.