Experimental Design for Extraction of Secondary Metabolites from Rauvolfia caffra Sond. Leaves: Biological and Chemical Characterization by Synchronous Fluorescence, Phosphorescence and FTIR Spectroscopy

S. Tomé and Principe (STP) islands have been studied in recent years for their wide range of medicinal plants which exhibit several biological activities of great medicinal interest for some diseases. Experimental design for optimization of several parameters was carried out by a full-factorial test of two levels of three factors for secondary metabolite extraction from Rauvolfia caffra leaves. The best conditions for highest extraction of phenolic compounds (i.e., 89.90 μmoles gallic acid equivalent/g leaves) were obtained at 25 °C in H2O and at 5 days of incubation. Several phytochemical assays were performed for characterization of these plant extracts, and the highest levels of TFC, DPPH and reducing power were obtained with aqueous plant extraction at 25 °C and for 5 days of incubation, whereas leaf extraction with water at 40 °C for 5 days of incubation revealed the highest levels of ABTS scavenging activity. The levels of SOD and superoxide radical scavenging activities were highest in plant extraction, with hexane at 25 and 40 °C for 5 days of incubation, respectively. The present report consists of a novel and intrinsic synchronous fluorescence and phosphorescence characterization of secondary metabolites from this plant extract. Intrinsic and non-destructive synchronous fluorescence was carried out in the range of 250 to 750 nm with a Δλ range of 5–30 nm, which exhibited several fluorescence peaks in hexane and aqueous plant extracts. On the other hand, intrinsic and non-destructive synchronous phosphorescence was also performed which also exhibited several peaks in aqueous and hexane extracts. 3D spectra of secondary metabolites confirmed the fluorescence peaks observed in SFS in plant extracts. FTIR spectroscopy was selected to investigate the structural properties of secondary metabolites in these plant extracts. Therefore, the present work describes a novel characterization of secondary metabolites by a non-destructive and intrinsic synchronous fluorescence technique for plant extracts.