## 1 Introduction  
Edible wild-grown _Boletus edulis_ mushrooms (porcini) have been largely appreciated for their flavor, nutritional value, and the extra health benefits provided by micronutrients and bioactive compounds (non-nutrient constituents) with biological significance, in particular antioxidant activity. Due to a high moisture content of >80%, fresh mushrooms are highly perishable [1] and are usually dehydrated into dried slices or powders, not only with the purpose of being consumed throughout the year, but also to be used as functional ingredients. Drying is an ancient traditional procedure embraced for its ease and for providing a year-round supply of mushrooms. In more recent years, researchers have focused on the compositional changes linked to the applied conditions of drying. In order to prolong the shelf life of mushrooms, different drying techniques have been employed, such as solar (open sun, solar dryers), hot air, lyophilization, microwave, or combined treatments, the specific applied drying conditions being responsible for the quality of the final product [2, 3, 4]. In relation to the conditions of operation, the complex process of mushroom dehydration may negatively impact the composition of some nutrients and bioactive compounds as well, but, on the other hand, may enhance the mushrooms' flavor [5]. The main mechanism for production of flavor/aroma compounds is based on the metabolism of fatty acids as a key pathway for C8 volatile components, and of sulfur and non-sulfur amino acids that act as precursors of aldehydes, alcohols, acids, or sulfur-containing aroma compounds [6]. Generally, drying at high temperatures changes the profile of phenolic and organic acids, decreases the content of polysaccharides and proteins, and increases the level of saturated fatty acids, due to different chemical reactions (oxidation, hydrolysis, Maillard reaction). Despite the fact that the total lipid content is low, fresh mushrooms constitute an advantageous source which can contribute to the uptake of essential fatty acids (in particular linoleic acid), but investigations on the recovery of some unsaturated fatty acids is required for their dried counterparts. The most frequently identified fatty acids in Basidiomycota are palmitic, oleic, and linoleic acids, with higher levels of the unsaturated ones [7]. New insights on the role of unsaturated fatty acids confirm a beneficial anti-inflammatory and antioxidant activity of omega 3-6-9 acids encapsulated in chitosan [8], while other studies on omega-9 fatty acids, such as oleic acid, have shown their neuroactive potential as analgesic agents [9]. The antioxidant activity and the content of total polyphenols, flavonoids, and volatile compounds may increase after drying. However, completing the conclusions of [PERSON] et al. given in their published review paper [5], it is no easy task to recommend the most suitable type of drying, due to the great variability of chemical composition even of the same species of investigated mushrooms, the different analytical methods involved for quantifying compounds (in particular aroma), and other factors that should also be considered, such as functional properties required for the final powder, biological activity, and cost of the drying technology. It has been considered that dried slices of _B. edulis_ mushrooms exhibit a strong attractive aroma [10], so that studying the changes in the profile of volatile compounds after drying is of high scientific and practical interest. Most studies on volatile compounds of _B. edulis_, using techniques such as SDE (steam distillation extraction)-GC-MS, SPME (solid-phase microextraction)-GC-MS, and LE (liquid extraction)-GC-MS, indicated a great loss of 1-octen-3-ol, the major contributor (86%) to the aroma of fresh _B. edulis_, and a total loss of 1-octen-3-one and (E)-2-octen-1-ol [11; 12]. [PERSON] et al.