From extract to crystals: Unlocking green nanotechnology towards recovery of bioactive compounds from Moringa oleifera via membrane distillation crystallization

• Low-energy and green MDCr for recovery of bioactive compounds from Moringa oleifera extract. • Eco-friendly and sustainable MDCr with stable salt rejection and permeate flux. • Controlled crystallization to maximize particle size distribution, crystallinity and phenolic content. • Demonstrated MDCr role in enriching essential microminerals from Moringa oleifera extract. • Highlighted MDCr feasibility as an alternative natural product extraction process. Membrane distillation crystallization (MDCr) is emerging as a green and efficient technology towards recovery of bioactive phytochemicals from natural extracts. The current study investigated recovery of Moringa oleifera (MO) crystals and high-purity water from the extract using the MDCr at varying feed temperatures, namely 55, 65 and 80 °C to optimize recovery of bioactive compounds. Real-time crystallization kinetics were monitored using the optical microscope, where supersaturated extract was sampled at 20 min and analyzed immediately. The MDCr process performance was monitored through permeate flux and salt rejection analysis. The permeate flux remained relatively stable even at high recovery factors (>73 %) with salt rejections maintained at 99 % for all feed temperatures. Precisely, the permeate flux was ∼0.9, 1.1, 1.5 kg·m −2 ·h −1 at 55, 65 and 80 °C, respectively. Like other previously reported studies, the increase in feed temperatures improved the rate of water recovery (flux) due to the rise in vapour pressure induced by the increased temperature difference (deltaT) across the membrane interface. The MO concentration was supersaturated at high recovery factors, triggering crystal formation. This is crucial for sustainable extraction of high-value compounds while recovering high quality water. Recovered crystals were analyzed using XRD, SEM, FTIR, ICP-OES and DPPH assay to understand their physicochemical characteristics. The MDCr-produced MO crystals revealed high ordered structures with enhanced phenolic content, particularly at 65 °C feed temperature. Increasing the feed temperature to 80 °C accelerated the nucleation, leading to faster crystal formation. However, partial degradation of bioactive compounds was detected. Based on antioxidant assays, MDCr-produced MO crystals presented increased radical scavenging activity (RSA) compared to raw ground MO powders, confirming phytochemical functional enhancement. Similarly, concentration of macrominerals was increased upon extract crystallization, offering advantaged applications in nutraceutical, medical, and food industry. This study highlighted the scalability of MDCr towards eco-friendly phytochemical extraction of MO, paving the way to natural product recovery.