Green, Ultrasound-Assisted Extraction for Carvacrol-Rich Origanum dubium Extracts: A Multi-Response Optimization Toward High-Value Phenolic Recovery

Origanum dubium, mainly grown in the Mediterranean region, is one of the less extensively studied species among the oregano class. Oregano species are recognized for their significant pharmaceutical properties, primarily attributed to carvacrol and other phenolic compounds. The goal of this study was to establish a sustainable method for the extraction of carvacrol, total phenolic, and total flavonoid compounds (TPC and TFC, respectively). Pulse-mode ultrasonic-assisted extraction (UPAE) was employed, using ethanol–water mixtures as green solvents, for the extraction of the bioactive compounds from the plant material. A Box–Behnken design (BBD) coupled with Response Surface Methodology (RSM) was applied to optimize the extraction process with respect to the extraction temperature, extraction time, ethanol-to-water ratio of the solvent and power amplitude of the ultrasonic processor. The responses of carvacrol (determined by HPLC-PDA), TPC, and TFC (determined by spectrometric methods) were evaluated by RSM. The statistical model identified the optimal extraction conditions, which were a combination of increased extraction temperature (70 °C) for 26 min with an intermediate ethanol–water ratio (60%) at the maximum processor’s power amplitude (100%). These conditions led to the optimal response of the three measured parameters. The optimized parameters represent a green and efficient approach to obtain bioactive-enriched extracts from Origanum dubium, suitable for potential applications in functional foods, preservatives, or other applications.