Green extraction of bioactive compounds from Thuja orientalis leaves using microwave- and ultrasound-assisted extraction and optimization by response surface methodology

Thuja orientalis is a medicinal plant. To extract its bioactives on a large scale, an efficient and eco-friendly method is required. In this study, two techniques, microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE), were optimized using response surface methodology (RSM) with 70% hydro-ethanol as an extractant. The responses included total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity measured through DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity (RSA) assays, and metal chelating activity (MCA). Well-fitted models were obtained for both techniques. In MAE, the optimized conditions were solvent-to-feed ratio (SFR) 35 mL/g, power 640 W, and time 90 s with optimum TPC of 540.4 mg gallic acid equivalent (GAE)/g dry weight (DW), TFC of 63.03 mg rutin equivalent (RE)/g DW, DPPH-RSA of 69.17%, ABTS-RSA of 77.69%, and MCA of 53.46%. In UAE, the optimum conditions were amplitude 90%, time 2 min, and SFR 35 mL/g and the optimum response values were TPC of 190.5 mg GAE/g DW, TFC of 48.59 mg RE/g DW, DPPH-RSA of 81.73%, ABTS-RSA of 73.63% and MCA of 63.81%. Scanning electron microscopy showed that both MAE and UAE effectively fractured the cell matrix. Both techniques were found highly effective, MAE being more efficient in TPC, TFC, and ABTS-RSA, while UAE showed higher efficiency in DPPH-RSA and MCA. Overall, MAE can be used on an industrial scale for the extraction of polyphenols, antioxidants, and metal chelators from Thuja orientalis being a less time- and solvent-consuming green technique.