Interactive effects of solvent extraction and drying methods on LC-ESI-QTOF-MS/MS-based characterization of bioactive phenolics and antioxidant activities in duckweed (Wolffia globosa)

The combination of drying methods and solvent media used profoundly impact quantitative and qualitative recovery, as well as the concentration of specific spectra of bioactive compounds. The study evaluated individual and interactive impacts of drying methods and solvent media on bioactive compounds and bioactivities from Wolffia globosa (wolffia), namely phenolics, flavonoids, carotenoids, tannins, vis-à-vis antioxidant activities with an aim to determine the best combination for the target bioactive spectra. The bioactive compounds from oven dried (OD), sun dried (SD) and freeze dried (FD) wolffia were extracted using three solvent media viz. 100% ethanol, 50% aqueous ethanol, and water. The results indicated that combination of FD and 100% ethanol yielded the highest quantity of total phenolic content (TPC; 830.40 mg GAE/g), total flavonoid content (TFC; 91.02 mg QE/g), total tannin content (TTC; 18.44 mg TAE/g), total carotenoid content (TCC; 2.34 mg/g), chlorophyll-a (Chl-a; 17.95 mg/g), and exhibited the highest DPPH⋅ (74.01%), ABTS+⋅ (79.66%) and FRAP (1545.87 µM FeSO₄/g) antioxidant activities. The highest chlorophyll-b (Chl-b; 5.75 mg/g) was found in FD samples extracted with water. Significant individual as well as interactive impacts of drying methods and solvent media were evident for extraction yield, total phenolic compounds and total tannin content and antioxidant activities namely DPPH & FRAP. However, only individual impacts but no interactive effects were evident with respect to TFC, TCC, and ABTS+⋅ antioxidant activity. This study demonstrated that FD combined with 100% ethanol extraction effectively preserved majority of unstable bioactive compounds and antioxidant activities. Metabolite profiling of extracts from differently dried samples for 100% ethanol identified 67 unique compounds, including 12 phenolic acids, 20 flavonoids, and 35 other polyphenols, with 44, 30, and 35 unique compounds in FD, SD, and OD, respectively. This study demonstrated that FD combined with 100% ethanol extraction was highly effective in preserving unstable bioactive compounds and antioxidant activities.

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