Optimization and Comparison of Microwave, Ultrasound, and Conventional Techniques for NaDES-Based Eco-Efficient Extraction of Antioxidant and Alpha-Amylase Inhibitory Bioactives from Holarrhena antidysenterica Seeds

In pursuit of a sustainable process for extracting bioactives from Holarrhena antidysenterica seeds, the current study explored three techniques, including advanced microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), and conventional heat-assisted extraction (HAE). A green natural deep eutectic solvent (NaDES), choline chloride–urea (CCU), was used as extractant. Each technique was systematically optimized according to response surface methodology (RSM) based on single-factor experiments. Response factors included total phenolic content (TPC), total flavonoid content (TFC), total condensed tannin content (TCT), DPPH radical scavenging activity (RSA), metal-chelating activity (MCA), and α-amylase inhibitory activity (AIA). Modeling was authenticated by statistical analysis and validation studies. For HAE, the optimal conditions (40 mL/g SSR (solvent-to-solid ratio), 70% DES concentration, and 200 rpm shaking speed) resulted in a TPC of 10.08 mg GAE/g DW, TFC of 30.38 mg RE/g DW, TCT of 5.06 mg CE/g DW, RSA of 2.48 mg AAE/g DW, MCA of 91.82 mg EDTAE/g DW, and AIA of 67.33%. For MAE, under optimal conditions (40 mL/g SSR, 70% DES concentration, and 770 W power), TPC was 15.15 mg GAE/g DW, TFC was 72.29 mg RE/g DW, TCT was 2.79 mg CE/g DW, RSA was 2.75 mg AAE/g DW, MCA was 85.21 mg EDTAE/g DW, and AIA was 60.29%. For UAE, TPC was 12.99 mg GAE/g DW, TFC was 39.41 mg RE/g DW, TCT was 6.16 mg CE/g DW, RSA was 2.58 mg AAE/g DW, MCA was 94.67 mg EDTAE/g DW, and AIA was 72.51% under optimized conditions (40 mL/g SSR, 70% DES concentration, and 70 \(^\circ{\rm C}\) extraction temperature). As per the results, MAE surpassed HAE and UAE in TPC and TFC, whereas UAE exhibited superior performance in TCT, MCA, and AIA, while MAE was also highly time-saving. Thus, MAE coupled with choline chloride–urea DES can be selected as a viable strategy for obtaining bioactive principles from Holarrhena antidysenterica seeds.