Characterization of phenolic compounds in watermeal (Wolffia globosa) through LC-ESI-QTOF-MS/MS: assessment of bioactive compounds, in vitro antioxidant and anti-diabetic activities following different drying methods

The samples of Asian water meal (Wolffia globosa) grown in an outdoor earthen pond (0.06 ha) in northeastern India was subjected to three different drying methods namely oven drying (OD), sun drying (SD), and freeze drying (FD) to evaluate their influence on proximate composition, qualitative as well as quantitative compositions. We characterized phenolic compounds and evaluated proximate composition, total phenolic content (TPC), total flavonoids content, total tannin content, total carotenoids content (TCC), Vit C, in vitro antioxidant, and in vitro antidiabetic potentials in W. globosa. Crude protein (29.79%), crude fiber (9.8%), TPC (8.43 mg GAE g⁻¹), TCC (766.32 µg g⁻¹), and Vit C (560.12 mg/100 g) were significantly high (p < 0.05) in FD. Among antioxidant activities, DPPH (39.87%) and ABTS (12.86%) were significantly highest in FD wolffia while superoxide alkaline DMSO (138%) was the highest in OD samples. Drying methods as well as glucose concentrations had significant individual as well as interaction impacts on glucose uptake rates of wolffia at all concentrations of wolffia sample evaluated (1–5 mg L⁻¹). Further, the adsorption capacity of the samples was significantly increased with increasing glucose molar concentrations. The LC-ESI-QTOF-MS/MS identified and characterized 33, 21 and 12 compounds in FD, SD, and OD respectively. FD wolffia also had the most greenish color (significantly higher negative a* value). We expect that our results will be of considerable value to the food, pharmaceuticals and nutraceutical industries.