Abstract
Barleria lupulina Lindl. (Acanthaceae) as an ornamental plant has been widely used in folklore medicine due to its abundancy in polyphenolic compounds. The present study examined conditions for optimal extraction of antioxidants from B. lupulina leaf extracts by using the microwave-assisted extraction (MAE) method. The effects of ethanol concentrations, microwave power, and extraction time on total phenolic content (TPC), total flavonoid content (TFC), 1-diphenyl-2-picrylhydrazyl (DPPH), and 2,20-azino-bis (3-ethylbenzothizoline-6-sulfonic acid) (ABTS) were investigated by single-factor experiments. Response surface methodology (RSM) was applied to observe interactions of three independent variables (ethanol concentrations, microwave power, and extraction time) on the dependent variables (TPC, TFC, DPPH, and ABTS) to establish optimal extraction conditions. Quadratic polynomial equations in all experimental models yielded favorably with fitted models with R2 and R2adj of more than 0.90 and a non-significant lack of fit at p > 0.05. The optimal conditions for the extraction of antioxidant activity were established at 80% (v/v) ethanol, 400 W, and 30 s with TPC (238.71 mg gallic acid equivalent (GAE)/g sample), TFC (58.09 mg QE/g sample), DPPH (87.95%), and ABTS (89.56%). Analysis by ultra-high-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UHPLC-QTOF/MS) successfully identified four new phenylethanoid glycoside compounds in the species.
Highlights
Polyphenols are a group of phytochemicals produced by plants as secondary metabolites
The present study investigated the effects of solvent concentrations, extraction time, and microwave power on extraction efficiency using microwave-assisted extraction (MAE) procedures conducted in single-factor experiments
Based on single-factor analysis, Response surface methodology (RSM) was applied by using Design Expert software (Version 10) to construct a Box–Behnken design (BBD) with five central-point replicates to determine the effects of variables on responses
Summary
Polyphenols are a group of phytochemicals produced by plants as secondary metabolites These compounds are known to give health benefits to humans, including antiaging, anti-tumor, anti-carcinogenic, and anti-glaucoma properties [1]. Flavonoids are a family of polyphenols with subclasses, including flavones, flavanols, isoflavones, flavanones, and chalcones They are known to be highly effective antioxidants and possess anti-inflammatory, antimicrobial, antiviral, anti-mutagenic, and anti-carcinogenic properties [3,4,5]. Previous studies have shown that RSM was useful in establishing optimal conditions for the extraction of antioxidant compounds and their activities [39,40,41]. The MAE is an efficient method due to its ability to extract bioactive compounds from B. lupulina leaves in a shorter time period as compared to Soxhlet and ultrasound-assisted extraction (UAE) [42]. RSM was utilized to establish the optimal conditions preceding the ultra-high performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UHPLC-QTOF/MS) to determine the bioactive compounds
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