Thermal-assisted recovery of antioxidant compounds from Bauhinia forficata leaves: Effect of operational conditions

Abstract

Herein, the extraction of antioxidant compounds from Brazilian orchid tree leaves (Bauhinia forficata Link), also known as “pata-de-vaca” or “pezuña-de-vaca,” is optimized using thermal-assisted solid-liquid extraction. The combination of operational conditions including the temperature (32–74 °C), ethanol percentage (13–97 %), and solid/liquid ratio of leaves and ethanol (1:10–1:60; w/v) was employed using a rotational central composite design. The extracts were evaluated for total phenolic compounds (TPC), total flavonoid compounds (TFC), and antioxidant capacities by the radical monocation reduction of 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+), free radical scavenging activity of 2,2′-diphenyl-β-picrylhydrazyl radical (DPPH), and ferric reducing/antioxidant power (FRAP). The phenolic profile of the optimized extract was also obtained using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry. The statistically evaluated results revealed that the optimal operational conditions for the recovery of antioxidant compounds from plant leaves included 73.5 °C, 51 % ethanol, and a solid/liquid ratio of 1:40. Under these conditions, the obtained values were 74 milligrams of rutin equivalent per gram of dried material (mg RE/g dm), 45 mg RE/g dm, 128 micromoles of Trolox equivalent per gram of dried material (μmol TE/g dm), 121 μmol TE/g dm, and 380 micromoles of Fe2+ per gram of dried material (μmol Fe2+/g dm) for TPC, TFC, and ABTS+, DPPH, and FRAP assays, respectively. The optimized extract mainly comprised kaempferol and quercetin derivatives, indicating that Bauhinia forficata Link leaves are an important source of antioxidant compounds.