Enhancing phenolic and flavonoid recovery from Vietnamese balm using green solvent-based ultrasonic-enzymatic-assisted extraction.

The research explored the extraction of phenolic and flavonoids from Elsholtzia ciliata (Vietnamese balm) using a natural deep eutectic solvent (NADES)-based ultrasonic-enzymatic-assisted extraction (UAE-EAE) technique. A range of NADESs was evaluated to investigate the most suitable solvent system. The NADES synthesized from lactic acid and choline chloride provided the highest recovery of phenolics and flavonoids. Single-factor experiments were conducted to assess how individual process variables influence the recovery of phenolics and flavonoids. Key factors affecting extraction performance were assessed using the Plackett-Burman approach. Optimal conditions were established through the Box-Behnken Design model. The optimal extraction parameters for TPhC were determined as a solid-to-liquid ratio (SLR) of 1:59 g/mL, water content (WC) of 12 %, ultrasonic temperature of 43 °C, ultrasonic time of 6.88 min, and incubation time of 6.33 min. For TFlC, the optimal conditions were established at SLR of 1:67 g/mL, WC of 14 %, and enzyme activity of 1.28 U/g. Under these optimized conditions, UAE-EAE achieved the maximum recovery of total phenolic content (36.41 ± 2.50 mg GAE/g) and total flavonoid content (18.74 ± 1.28 mg QE/g). A second-order kinetic model was adopted to analyze the extraction mechanism. Structural and surface changes in the plant matrix before and after extraction were further investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). This method demonstrates high efficiency and eco-friendliness in extracting plant-derived bioactive compounds using NADES-based UAE-EAE.