**5. Conclusion**

*Antioxidants*

**Figure 5.**

different from ethanol, which is an environmentally safe solvent being a good choice for SFE processes, and can be used in the extraction of natural products [80, 81]. Water is also a very attractive cosolvent for natural product extraction due to its

For antioxidant compound extraction and recovery by SFE, several vegetable matrices were used, such as seeds, fruits, leaves, flowers, rhizomes, roots, fruit peels, and tree branches. The SFE process consists basically in the extraction of soluble compounds present in the solid matrix by a supercritical solvent and then separates these compounds from the solvent after depressurizing the system. In order to achieve an efficient and adequate extraction, several factors must be taken into account, having a careful control of the operating conditions and process step

Initially, the raw material must pass through a pretreatment stage before being fed into the fixed bed extractor; this procedure is performed to prepare the solid particles, allowing a greater efficiency to be achieved in the extraction process [83]. As shown in **Figure 5**, after the raw material is collected, one of the first stages of its pretreatment is the solid matrix moisture reduction, for example, drying leaves in an oven with air circulation. Generally, the plant matrix moisture should not exceed 14% (wet basis). Another important step is the moisture content determination by the distillation method of the Jacobs immiscible solvent, with the purpose of knowing if the quantity of water in the sample is adequate for the supercritical extraction process. The sieving stage is applied to standardize and determine the average particle size of the solid particles. The real and apparent density and bed porosity determination is also very important as they affect the particles packaging in the extraction vessel and conse-

high polarity, which considerably increases the polarity of Sc-CO2 [79].

quently the solvent flow and the mass and heat transfer processes [35, 82].

After a suitable pretreatment, the solid matrix is placed in an extraction vessel forming a fixed bed. Depending on the compounds of interest, the supercritical solvent (Sc-CO2) or solvent + cosolvent is fed by the solvent pump and/or cosolvent into the extraction vessel, where it continuously flows through the fixed bed and dissolves the extractable components from the solid matrix. The mixture of solutes that is removed from the solid matrix is called extract. In the separation step, the mixture formed by the solvent extraction + extract leaves the vessel and feeds the separator (collection flask) where the mixture is separated by rapid reduction of

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optimization [35, 36, 82].

*Scheme of the SFE procedure of plant matrices.*

The identification of new natural antioxidant compounds is of great interest to the food, pharmaceutical, and cosmetic industry in order to find possible alternatives to synthetic antioxidants. In this way, plants such as *C. sicyoides* and *R. officinalis* have been extensively studied for their antioxidant activity. The *C. sicyoides* extract obtained by SFE has a neuroprotective and anti-inflammatory effect; these effects are associated with the presence of phenolic compounds and the high antioxidant activity in the extract. *R. officinalis* extract is antibacterial, antifungal, anti-inflammatory, and effective, associated with the presence of carnosic acid, carnosol, rosmarinic acids, and hesperetin. It has been corroborated that these plants contain chemical compounds that exhibit the capacity of FRSs and reduce the onset of different diseases. Finally, obtaining extracts from plant matrices using environmentally safe extraction technology such as SFE represents a great opportunity to obtain bioactive compounds.
