Response surface methodology guided process optimizations, modeling and biofunctional analysis of phytochemicals from Nigella sativa seeds as a potential antifungal agent

Abstract

Nigella sativa L. or black cumin is rich in several bioactives, exhibiting excellent biofunctional properties; hence could be exploited for providing protection against storage fungi. Response surface methodology driven ultrasonic assisted extraction (UAE) and microwave assisted extraction (MAE) variables were optimized to get maximum yield of bioactive phytochemicals from N. sativa seeds. -. The optimal extraction conditions were determined as: amplitude 32.02 kHz, extraction time 13.12 min, solvent to solute ratio 35.88 mL/g for UAE; and microwave power 674.18 W, time 168.21 s, solvent to solute ratio 70.09 mL/g for MAE. Extraction kinetic models demonstrated the initial increasing rate of mass transfer, depending upon individual extraction variable. Microstructural analysis clearly confirmed the influence of ultrasonic cavitation acoustic and microwave energies on the matrix wall, resulting intense rupture and disintegration to release phyto-constituents immediately. Ultra Performance Liquid Chromatography-Quadrupole-Time of Flight–Mass Spectrometric (UPLC-QTOF- MS) analysis of ethanolic concentrate (ENS) revealed fifty-seven diverse phytochemicals, dominated by thymoquinol-β-glucopyranoside, kaempferol-3-O-pentoside, nigellimine, nigellimine-N-oxide, nigellamine A1, thymoquinol, thymoquinone, dithymoquinone and nigellidine-4-O-sulfite. ENS exhibited excellent antifungal action against A. flavus 2838 (27.6 μg/mL) followed by A. flavus 2547 (34.8 μg/mL) and A. flavus 837 (46.3 μg/mL). Antifungal action was further confirmed through the inhibition of fungal ergosterol content (%), correlating with the in silico analysis pertaining to the ligand protein interaction between individual component and sterol 14-α-demethylase. Nigellamine A1, kaempferol-3-O-pentoside and nigellidine-4-O-sulfite were found to be promising as they exhibited favourable interactions like H-bonds, electrostatic bonds, hydrophobic bonds and with weak van der Waals bonds with the target protein.