Optimization of ultrasound-assisted extraction of total phenolics and flavonoids from the leaves of Lobelia nicotianifolia and their radical scavenging potential

Abstract

Optimization of the ultrasound-assisted extraction (UAE) for total phenolics content (TPC) and total flavonoid content (TFC) from leaves of Lobelia nicotianifolia Roth. was worked out. Full factorial design (FFD) was used to study the effects of three independent variables (methanol ratio, temperature, and extraction time), each with three levels. The optimal combination for maximum efficiency of extraction and antioxidant activity was 75.25% methanol, 62.72 ​°C temperature, and 9.44 ​min duration. The extract made under these conditions had higher TPC and TFC of 23.78 ​mg TAE/g dry weight and 20.21 ​mg QE/g dry weight, respectively. Furthermore, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays of the extract showed higher antioxidant potential with 95.78% and 97.26% radical scavenging activity (%RSA), respectively. Scanning electron micrograph (SEM) of leaves showed ultrasonication-induced morphological changes and cellular damage. Fourier-transform infrared (FTIR) analysis of conventional extraction and extracts obtained by UAE showed remarkable differences in peaks. Therefore, the UAE method seems to be superior to the conventional method for extracting total phenolics and flavonoids.