## 3 Results and Discussion
### Fagus sylvatica  
In beech wood, there were no substantial changes in the compounds, therefore results showed less degradation due to thermal modification. Among the main bioactive compounds found in beech, squalene (detected by GC-MS) and ar-tumerone (detected by SPME) are worthy of attention (Table 1).  
Squalene (2,6,10,15,19,23-hexamethyl-2,6,10,14,18,22-tetracosahexaene) is a triterpene that acts as an intermediate in the biosynthesis of phytosterol or cholesterol in plants, animals and humans. In its pure form, it is a colourless, odourless, tasteless, and highly stable hydrocarbon oil that is biocompatible with skin, non-toxic and non-irritant, and prevents moisture loss, restoring skin's suppleness and flexibility [40]. It presents remarkable antioxidant and antibiotic activities derived from its chemical structure of six double bonds. Squalene is used to make other chemicals such as drugs and rubber chemicals. It is used in cosmetics including sunscreen lotions, lipstick foundations, nail products, hair conditioners and moisturizers, and it is also used as a dietary supplement and in traditional medicine for disease management and therapy [41]. It offers a wide range of benefits such as embilient, hydrating, high spreadability, light consistency, non-greasy texture, rapid transdermal absorption, and reduction of skin damage by UV radiation; moreover, it has been used in healing eczema and the protection against ageing and wrinkles. It is also used in the preparation of stable emulsion as an adjuvant for vaccine delivery stimulating the immune response and increasing the patient's response to the vaccine. Although squalene by itself is a weak inhibitor, it has been shown to prevent or arrest tumour growth in conjunction with anticancer drugs in various experimental tumour models [42; 43]. The liver oil of sharks from the deep sea represents the richest natural source of squalene. Important reasons are limiting the use of this source, such as the presence of persistent organic pollutants in the sea, which can still be found in the purified squalene; the regulations against the overfishing of sharks; and the increasing trend among the consumers towards the use of plant-based products. Squalene has multiple applications due to its unique properties.  
Considering the abovementioned factors, there is a great interest in finding new, natural, mainly vegetable, sources for squalene. The most relevant plant sources of squalene are oils extracted from amaranth, olive, palm, rice, wheat germ, grape seed, peanut, and soybean [44]. Most vegetal oils are obtained by mechanical pressing or extraction with solvents like hexane; therefore, water extraction can offer a valid alternative of green chemistry for obtaining these oils. The growth in the cosmetics and pharmaceutical industry, along with the increasing research in the oncology segment, are the major factors driving the growth of the squalene market.  
The terpene ar-Tumerone is a compound found mainly in curcumin, a perennial plant cultivated throughout tropical Asia, India, and China. This compound has been investigated in clinical trials for its potential therapeutic properties, including anticancer activity [45]. Ar-Tumerone acts through various mechanisms, including the induction of apoptosis, inhibition of angiogenesis, and modulation of tumour suppressor genes [46]. A new study, analyzing the effect that this substance brings to brain cells both in vitro and in vivo, showed that when brain cells were exposed to Ar-Tumerone, neural stem cells increased in number through greater proliferation. Furthermore, these newly formed neural stem cells also increased the number of fully differentiated neuronal cells, indicating that they immediately initiated a healing effect [47].