## 3 Results and Discussion
### Effect of Cooking on Volatiles' Profiles  
The volatile compounds determined in fresh and roasted mushrooms of _P. eryngii_ strain CS3 and _P. ostreatus_ strain LGAM 3002 cultivated on wheat straw are shown in Table 3. Besides water loss, roasting caused significant alterations in the volatiles' profiles for both species. Overall, the number of volatile compounds decreased from 35 to 27 in roasted _P. eryngii_ and increased from 35 to 41 in roasted _P. ostreatus_ (Table 3). The percent abundance of volatile alcohols decreased by 65% and 77% in roasted _P. eryngii_ and _P. ostreatus_, respectively; the same trend was followed by fatty acid methyl esters, which were almost eliminated (they decreased by 95% and 97% in roasted _P. eryngii_ and _P. ostreatus_, respectively). Similarly, ketones, aldehydes and eight-carbon compounds decreased by 66%, 64% and 65% in _P. eryngii_ and by 85%, 9.0% and 81% in _P. ostreatus_. Elimination of FAME during the freeze-drying of _A. bisporus_ has been reported by [PERSON] et al. (2016) [27]. In addition, roasting resulted in the formation of nitrogen-containing heterocyclic compounds (17 pyrazines, one pyrrole and one oxazole) and two sulfur compounds, i.e., substances with low odor threshold values, known to enrich food flavor with meat- or roast-like aromas [63]. The predominant compounds in roasted _P. eryngii_ were 1-octen-3-ol (mushroom-like flavor), followed by hexanal (green and woody), toluene (sweet, solventy,woody, roasted coffee) and undecane (gasoline-like). In roasted _P. ostreatus_ 1-octen-3-ol also predominated, followed by 3-octanol (mushroom, buttery), toluene, 3-octanone (mushroom, ketonic, cheesy) and 3-ethyl-2,5-dimethyl pyrazine (hazelhut, nutty). Several aroma compounds detected in fresh and cooked mushrooms originate from the enzymatic and oxidative decomposition of unsaturated fatty acids or from reactions between amino acids and carbonyl compounds, i.e., the Maillard reactions and the Strecker amino acid degradation which leads to the formation of Strecker aldehydes and other flavor-active compounds [48; 64; 65]. The extent of these transformations depends on the types of compounds involved, temperature, pH and reaction time [65; 66; 67]. Regarding the influence of temperature, the volatile compounds produced by lipid oxidation (aldehydes, ketones, and aromatic hydrocarbons like hexanal, octanal, benzaldehyde and toluene) are formed at relatively low temperatures, even at room temperature [45]; this provides an explanation for their presence in the fresh mushroom samples (Table 3). By contrast, Maillard and Strecker reactions take place at higher temperatures. Literature data consider temperatures around 120-130 \({}^{\circ}\)C as optimal for the formation of Maillard reaction products with favorable sensory characteristics [68] as well as for the formation of compounds with sulfur and nitrogen groups [69; 70], e.g., pyrazines, Strecker aldehydes, dimethyldisulfide and pyrrole (detected in the roasted _Pleurotus_ samples; Table 3). It is noteworthy that _Pleurotus_ mushrooms contain significant amounts of Maillard reaction precursors, namely free amino acids, reported to comprise 37.1-41.6% of crude protein [44] and glucans, which comprise 40-50% \(w/w\) of the total content on a dry weight basis [71]. In addition, the Strecker aldehydes 2-methylbutanal, 3-methylbutanal, methional, phenylacetaldehyde and benzaldehyde, detected in the roasted samples (Table 3) derive from isoleucine, leucine, methionine and phenylalanine [67; 72], i.e., amino acids that are present in the mushrooms studied [44]. Pyrazines are heterocyclic aromatic compounds, formed by the reaction between amines and dicarbonyl compounds through Strecker's degradation [73; 74]. They provide roasted, nutty flavor notes to the aroma of thermally-treated food products, even at very low amounts, because of their very low odor thresholds [75; 76].