Phenolic compounds from Cymbopogon citratus (DC.) Stapf leaf extracts: extraction optimization, flavonoids LC-MS characterization and stability assessment

The extraction of phenolic compounds from Cymbopogon citratus (DC.) Stapf ( C. citratus ) leaves was optimized by applying a response surface methodology (RSM). A centered composite design (CCD) was carried out to analyze the influences of liquid-solid ratio (mL/g), temperature (°C) and extraction time (min) on the extraction yields (EY), the total phenolic contents (TPC), the total flavonoid contents (TFC) and the antioxidant activity (DPPH and FRAP). The aging of the optimized extract was tracked over 150 days under various storage conditions by assessing the reduction in TPC and major flavonoids using colorimetric assays with a UV-vis spectrophotometer and HPLC–ESI–MS quantification, respectively. The optimization results showed that the extraction condition corresponding to 12.4 mL/g of powder at 49.1°C for 157.1 min was the best condition for this combination of variables. Under this condition, extraction yields, TPC, TFC, DPPH and FRAP were 16.5%, 238.8 mg GAE/g, 223.5 mg QE/g, 96.8 µg/mL and 371.2 mg TE/g, respectively. Ten major flavonoids were identified and quantified, of which luteolin 6- C -glucosyl-2"- O -rhamnose and luteolin 7- O -neohesperidoside were the most abundant with 9.7 and 8.3 mg/g of extract, respectively. After 150 days, TPC, flavonoids and antioxidant properties of the dry extract were better preserved (over 75%) than those stored in aqueous and hydroalcoholic solvents at –20°C and 4°C. The results showed that increasing the storage temperature to 25 and 50°C reduced the storage time to 90 and 60 days, respectively. It was also found that di- C -glycosyl flavonoids in the extracts were the most stable compounds compared to O -glycosyl flavonoids. This study highlights the high phenolic compound content of C. citratus extracts, an indicator of its pesticidal potential and a promising source for the biopesticide development.