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The aim of the study was to identify the best evaporation process that allows obtaining a dry methanol extract of Moringa oleifera leaves rich on phytochemicals and showing a significant antioxidant activity. The liquid extract, prepared by the maceration of the leaves of M. oleifera into 70% aqueous methanol at room temperature, was evaporated using three solvent evaporation methods, these included evaporation in air at room temperature, with rotary evaporator and in an oven at 40 °C. Extracts were investigated for total polyphenols content (TPC), total flavonoids content (TFC), total condensed tannins content (TCTC), identification and quantification of some phenolic compounds by high-performance liquid chromatography coupled with photodiode array and mass spectrometry detection (HPLC-PDA-ESI/MS) and evaluated for antioxidant activity. The analysis of extracts by HPLC-PDA-ESI/MS showed that the dry extract obtained in dark after oven evaporation exhibited the highest amounts of 13 out of 19 phenolic compounds; quinic acid, gallic acid, 4-O-caffeoylquinic acid, caffeic acid, trans-ferulic acid, apigenin 7-O-glucoside, quercetrin, kaempferol, naringenin, apigenin, luteolin, cirsiliol and cirsilineol. In all extracts, quinic acid, 4-O-caffeoylquinic acid, rutin and quercitrin were present as the main compounds. The chemical composition and the antioxidant potential of the methanol extract are strongly affected by the method of evaporation of the solvent used. The highest values of TPC, TCTC and the antioxidant activity were provided by the extract obtained when the solvent was evaporated in oven. These results showed that the evaporation of the solvent in the oven at 40 °C was the best evaporation method to be used for the extraction of phytochemicals from the leaves of M. oleifera by cold maceration method using 70% aqueous methanol as solvent.
Bennour et al. (Mon,) studied this question.