## 1 Introduction  
The development of new scientific techniques to improve aspects of life in an environmentally friendly way is demanded by society in general and is a principle that is addressed by the scientific community. In recent years, the use of CO\({}_{2}\) under supercritical conditions (i.e., above 304.1 K and 73.8 bar) has been considered as a green and environmentally friendly evolution when compared to more conventional methods [1; 2]. The effectiveness of this approach in processes involving extraction [3; 4], micromization [5; 6], encapsulation [7; 8] or impregnation [9; 10], while removing or reducing the use of organic solvents that were widely used decades ago in industry, represents a great advance in meeting the current demands of society. In accordance with the above principles, the supercritical antisolvent process (SAS) exploits the ability to precipitate compounds that are not soluble in supercritical CO\({}_{2}\). A solution of an active substance is sprayed through a nozzle into a precipitator that contains CO\({}_{2}\) under supercritical conditions. Once the substances are in contact, scCO\({}_{2}\) diffuses into the organic solvent, thus leading to supersaturation of the solution, which in turn results in precipitation of the active substance. A large number of authors have used this method [11; 12] to micronize or encapsulate various substances. In the work described here, the matrix selected to deposit the antioxidants as precipitates was mesoporous SB-300 silica, mainly due to its large specific surface area and high porosity [13]. Some authors have already studied supercritical impregnation onto porous matrixes such as activatedcarbon, carbon-sulfur composites [14], silica MCM-41 with nanometallic (Ru, Rh, Pd) and bimetallic (Ru-Rh, Ru-Pd, Rh-Pd) deposition [15] or cobalt oxide nanoparticles [16] on MCM-41, Pd nanoparticles into mesoporous silica SBA-15 [17], or Ru nanoparticles onto SiO\({}_{2}\) SBA-15 [18]. In the study described here, the aim was to examine the supercritical deposition of a natural antioxidant and to carry out an in-depth study into the effects of different SAS configurations. The active principles selected were quercetin (Q), a flavonoid with a range of relevant properties such as anti-inflammatory, antibacterial, anticancer and cardiovascular health [19; 20], and mangiferin (MNG), a common polyphenol with numerous therapeutic treatments that include anti-viral, anti-oxidant or anti-diabetic activities [21; 22]. The effect of these active principles is very small due to their low solubility in water, which complicates oral delivery and bioavailability [23; 24]. The use of an SAS process reduces the particle size of these compounds and enhances the solubility in aqueous media. The micromization of MNG and Q using a SAS process has previously been studied by several authors. Micro- (MPs) and nanoparticles (NPs) of MNG were obtained by [PERSON] et al. [25] using N,N-dimethylformamide (DMF) as co-solvent to give MPs with an average size of 0.53 \(\upmu\)m. [PERSON] et al. [26] obtained MPs and NPs with sizes between 0.22 and 1.44 \(\upmu\)m using acetone and dimethyl sulfoxide (DMSO) as a co-solvent. As far as Q is concerned, MPs and NPs were obtained by several authors [27]. For example, [PERSON] et al. reduced the particle size by a factor of 4.1 [28], [PERSON] et al. obtained MPs and NPs with sizes between 0.12 and 0.45 \(\upmu\)m, [PERSON] et al. [29] succeeded in precipitating MPs and NPs with sizes between 0.15 and 0.35 \(\upmu\)m and [PERSON] et al. [30] successfully precipitated MPs and NPs with sizes between 0.15 and 1.25 \(\upmu\)m.  
The coating agent selected was cellulose acetate phthalate (CAP), a cellulose derivative that has previously been studied [31] and used to control drug delivery [32] due to its resistance to gastric fluids and its degradation in intestinal fluids at a pH of around 6.8 [33].