Rosmarinus officinalis L., or rosemary, is an evergreen, aromatic, medicinal plant belonging to the Lamiaceae family. Typical of the Mediterranean area, rosemary is used for its flavoring characteristics and therapeutic benefits; in addition to being part of the Mediterranean diet, it was (and still is) widely used in traditional medicine to prevent colds and treat wounds, rashes, headaches, indigestion, and renal colic. 
Depending on the chemotypes and on the collection period of the aerial parts of the plant, the composition of rosemary extracts can vary, presenting different ratios of terpenes, phenolic acids, and flavonoids. The aforementioned compounds constitute the most bioactive molecules, giving rosemary antioxidant, antimicrobial, antibacterial, anti-inflammatory, and cognitive-enhancing properties. The quality of rosemary extracts is evaluated mainly by considering non-volatile phenolic diterpenes carnosic acid and carnosol; rosmarinic acid, a phenolic acid; and volatile terpenes/terpenoids like 1,8-cineole, α-pinene, and camphor.
High temperatures during the extraction processes degrade thermolabile compounds, leading to a reduction of extract bioactivity. For this reason, conventional extraction techniques such as steam distillation (SD), hydrodistillation (HD), maceration, and Soxhlet extraction evolved and, in industrial environments, have been replaced by modern techniques capable of reducing operating temperatures and process duration by modulating extraction parameters. In addition, modern extraction procedures aim to minimize use of organic solvents which can contaminate the final product and be harmful for the environment. The most promising modern methods to obtain rosemary extracts and essential oils (EOs) are supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), ultrasound-assisted extraction (UAE), and microwave-assisted extraction (MAE). 
Extracts obtained by SFE show greater yield and antioxidant activity compared to low-pressure HD processes. In 2014, Pilar Sanchez-Camargo et al  developed a two-step procedure consisting of the initial supercritical CO2 removal of waxes and oleoresin at 300 bar and 40 °C, followed by CO2 SFE with 7% ethanol as cosolvent at 150 bar and 40 °C to improve carnosol and carnosic acid recovery.
PLE is a widely used method to recover phenolic compounds from rosemary: antioxidant constituents of different polarities (e.g., carnosic and rosmarinic acids) are efficiently extracted using water and ethanol after 20 minutes at high temperature (200 °C).  It has been reported that an increased yield of carnosic acid and carnosol is obtainable by performing a 20-minute PLE extraction with hexane at 100 °C and 100 bar compared to 5 hours of CO2 SFE at 200 °C and 300 bar. 
UAE and MAE have the capability of accelerating the extraction process, leading to higher yields compared to traditional solid/liquid methods. Bellumori et al  reported increased total phenol content in UAE performed for 10 minutes at 19.5 kHz and 140 W with ethanol as solvent (e.g., “remarkably high rosmarinic acid content”). When n-hexane was the extraction solvent, UAE generated a higher final terpenoid content with greater yields of carnosic acid compared to the traditional method.
Microwaves may be combined with distillation techniques for rosemary EOs. In one study, a technique known as microwave hydrodiffusion and gravity (MHDG) produced rosemary EO in 15 minutes compared to 180 minutes for hydrodistillation.  MHDG used no solvent, extracted higher levels of camphor, and demonstrated superior antioxidant properties.
In the future, the combination of novel extraction techniques and the refinement of existing ones will lead to a higher quality of rosemary extracts and EOs, improving the beneficial therapeutic properties of this interesting medicinal plant. 
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