Synergistic enhancement of bioactive release and antibacterial activity by NADES extraction from solid-state fermentation-pretreated Strychnos spinosa Lam

A tough African fruit hides its powerful phenolic compounds behind a fortress of plant cell walls—until a clever combo of fermentation and green solvents cracks it open.

Strychnos spinosa, a sub-Saharan plant, packs its phenolic treasures deep within a resistant lignocellulosic matrix. Conventional extraction methods struggle to break through. But a new study offers a game-changing strategy: pair solid-state fermentation with natural deep eutectic solvents (NADES).

Researchers fermented the plant material with Aspergillus oryzae, then extracted it using a choline chloride-lactic acid NADES. The result? A dramatic boost in yield. The fermented NADES extraction (F-NADES) achieved a total phenolic content of 16.85 mg GAE/g, far surpassing the non-fermented ethanol method at 10.25 mg GAE/g. The extraction rate constant also doubled, showing faster and more efficient recovery.

Microscopy and spectroscopy confirmed that fermentation physically disrupted the cell wall matrix, releasing bound compounds. Advanced metabolite profiling revealed that fermentation converted phenolic glycosides into more active aglycones, such as apigenin and luteolin. These changes translated into potent antibacterial effects: F-NADES showed minimum inhibitory concentrations (MIC) of 0.78–6.50 mg/mL and minimum bactericidal concentrations (MBC) of 1.56–12.50 mg/mL across all tested strains.

This synergistic approach not only maximizes bioactive release but also offers a sustainable, efficient path to natural preservatives—turning a tough nut into a treasure trove.

Key Points

• Fermented NADES boosts phenolic yield by 64% over ethanol.
• Fermentation disrupts cell walls, releasing bound bioactives.
• F-NADES shows strong antibacterial activity (MIC 0.78–6.50 mg/mL).