Process Optimization of Microwave-assisted Aqueous Extraction for Phytochemicals and Antioxidant Activity of Syzygium Cumini

This study optimized microwave assisted aqueous extraction of phytochemicals from Syzygium cumini leaf powder using water as solvent. Response surface methodology with a three factor Box Behnken design was used to quantify the effects of microwave power, extraction time, and particle size. Factor ranges were 360 - 900 W, 8 - 20 min, and 100 - 500 µm. Microwave irradiation was applied in pulsed mode to limit boiling. Process performance was evaluated using total phenolic content, total flavonoid content, total tannin content, and antioxidant activity measured by DPPH and ABTS assays. Numerical optimization predicted an optimum at 900 W, 18.94 min, and 276.54 µm. At these conditions, predicted responses were 305.44 mg GAE/g ds for total phenolics, 70.12 mg RE/g ds for total flavonoids, and 83.35 mg TAE/g ds for total tannins. Predicted antioxidant activities were 5.51 mM TE/g ds for DPPH and 5.78 mM TE/g ds for ABTS. Experimental validation was conducted at the nearest practical settings of 900 W, 20 min, and 273 µm. Measured values were 305.55 ± 0.07 mg GAE/g ds, 70.54 ± 0.05 mg RE/g ds, and 81.99 ± 0.03 mg TAE/g ds for total phenolics, total flavonoids, and total tannins, respectively. DPPH and ABTS reached 5.47 ± 0.03 and 5.74 ± 0.04 mM TE/g ds, respectively. The close agreement between predicted and measured responses supports the use of RSM to define an implementable operating window for aqueous microwave extraction of Syzygium cumini leaves.