Enhancing the recovery of bioactive compounds from rain tree (Samanea saman) seeds through optimized ultrasound-assisted extraction and response surface methodology

Abstract This study aimed to optimize ultrasound-assisted extraction (UAE) of phytochemicals and antioxidant properties from rain tree seed extract (RTSE) by evaluating ultrasonic power ratio, extraction temperature, extraction time, and ethanol concentration. Increasing power from 20 to 80% decreased total flavonoid content (TFC) and ferric reducing antioxidant power (FRAP) by 25–37%. Higher extraction temperatures (70°C) reduced antioxidant activities by up to 35% compared with mid-range conditions (50–60°C). Prolonged extraction times (50 min) caused declines of up to 28% in TFC and DPPH activity, showing the sensitivity of flavonoids to extended exposure. In contrast, total phenolic content (TPC) increased by 12–20% with higher temperature and time, suggesting thermal facilitation of phenolic release. Ethanol concentration displayed a parabolic effect, with 30–40% producing the best yield, while 10% or 50% caused 15–25% reductions. Second-order polynomial models accurately predicted extraction yield (EY), TPC, TFC, DPPH scavenging activity, and FRAP. The optimal UAE conditions 44% power, 60°C, 10 min, and 23% ethanol produced an EY of 17.36%, TPC of 0.0147 mg GAE/g DW, TFC of 0.033 mg QE/g DW, 60.44% DPPH activity, and 5.97 mmol Fe 2 ⁺/g DW FRAP, closely matching predicted values. LC-QTOF-MS profiling of the optimized extract revealed a metabolome dominated by flavonoid glycosides, phenolic esters, and isoflavones, with oxylipins and glycolipids also present. Major compounds included quercetin and luteolin derivatives, phenolic esters, and plant hormone conjugates. These findings highlight rain tree seeds as a rich source of bioactive compounds with potential applications in functional foods. Graphical Abstract