# Obtaining Aromatic Extracts from Portuguese
## 1 Introduction  
Lipophilic volatile compounds play a notable influence on the olfactory marketing strategy in the food, cosmetic and fragrance industries. Selective oils from natural origins are recognised as one of the main approaches to product improvement, whether to extend shelf life, in alternative medicine treatments or for sensory purposes [1, 2]. The compounds extracted from plants, namely essential oils, have distinct chemical compositions related not only to the species itself but also to agriculture practices, soil properties, climate conditionsand stage of development [3]. Over the last century, advances in the knowledge of chemical routes have proven the contribution of the environmental state in the secondary metabolism of plants [4]. Chemically unstable and easily isomerized, volatile fractions obtained by conventional extraction procedures (e.g., HD, steam distillation (SD), maceration (MAC), and Soxhlet (SOX)) show significant chemical alterations. The presence of light, heat and the existence of an organic solvent are some of the conditions that promote the decomposition of unsaturated or esterified molecules [5]. The thermal hydrolysis effect was observed in HD products by the formation of the \(p\)-cymene molecule, an aromatic monoterpene and precursor of the thymol and carvacrol (both isomers) compounds [6; 7]. This reaction can occur rapidly through dehydrogenated and oxygenated \(\gamma\)-terpinene, respectively [1; 8]. However, in the last three decades, SFE has increased the naturalness of the odour of the extracted products [9]. SFE is a green extraction technology and typically uses CO\({}_{2}\) as a solvent at a critical pressure of 73.8 bar and a minimum temperature of 32.1 \({}^{\circ}\)C [5]. In addition to its safety, chemical stability, low cost and availability characteristics [10], CO\({}_{2}\) can change its solvent capability by changing pressure and temperature, thus affecting the density of the fluid and the extraction efficiency [7; 11]. Generally recognised as safe by the Food and Drug Administration [9], CO\({}_{2}\) as a supercritical fluid is highly selective and favours the extraction of thermolabile bioactive compounds [7]. As shown by [PERSON] et al. [12], by using a SFE-CO\({}_{2}\) process with gradual decompression, different compounds can be collected in order of their molecular weight in different separators. In this work, the first separator was designed to capture the heavier substances (mainly sesquiterpenoids such as \(\beta\)-caryophyllene), and the second separator was designed for lighter components such as monoterpenoids (e.g., \(\gamma\)-terpinene, linalool and camphor). Depending on the system pressure, no EX was recovered in both separators simultaneously, as shown by [PERSON] et al. [13] using pressures from 150 to 400 bar and a temperature of 40 \({}^{\circ}\)C. No EX was obtained in the first separator at low pressure. Nevertheless, the product of the second separator has a similar chemical composition to those obtained in the severest extraction conditions, differing just in their relative concentration and yield. Comparable results were shown for several raw materials [7; 12; 13; 14; 15; 16; 17]. Thereby, to guarantee the selectivity and high solubility of the volatile fraction, normally the indicated SFE-CO\({}_{2}\) conditions are around 80 to 100 bar and 40 to 50 \({}^{\circ}\)C [11; 16]. Moreover, studies have reported a reduction of selectivity of the supercritical products when higher pressure and temperature values were applied, resulting in the co-extraction of long-chain lipids compounds [17]. Aiming to present these well-known concepts for traditional plant material from Northern Portugal, the main genotypes and sensory attributes of _T. mastichina_ were studied. _T. mastichina_ is an endemic and undershrub Iberian Peninsula herb, reaching more than 50 cm in height and blossoming from April to June [18]. Between the 215 species of genus _Thymus_[3], Portuguese _T.