## 3 Results and Discussion
### Volatile Composition
Other important volatile compounds presented in saffron stigmas belong to the family group of ketones (3) and alcohols (1), such as isophorone (V11); 1,4-cyclohexanedione, 2,2,6-trimethyl-(dihydropyrooxophorone, V14); 1-butanol, 3-methyl-(isoamyl alcohol, V2) and 2,6,6-trimethyl-2-cyclohexene-1,4-dione (4-ketioisophorone, V12). Regarding isophorone, isoamyl alcohol, and 4-ketioisophorone content, Greek saffron had a significant highest concentration of those compounds (1936 \(\mu\)g/g, 1018 \(\mu\)g/g, and 789 \(\mu\)g/g, respectively), with these values consistent with the results reported by [PERSON] et al. [34] in Greek saffron. Other studies also reported that safranal, isophorone, 4-ketoisophorone, and dihydrooxophorone were the main volatiles found in saffron stigmas from central Italy [35]. Moreover, isophorone also has antimicrobial and antioxidant properties [36]. With respect to dihydrooxophorone, the significant highest content was found in Iranian saffron with a concentration of 848 \(\mu\)g/g; this value was higher than those obtained in other studies for Iranian saffron (591 \(\mu\)g/g) [37]. The formation of oxidized and reduced isophorone-related compounds might be produced through an enzymatic process or may occur via oxidation and decarboxylation of safranal and further chemical reactions of other compounds [4]. The volatile compounds identified in the saffron samples were comparable to those reported in previous research. [PERSON] et al. [38] reported that some of the major compounds in Spanish, Greek, Italian and Iranian samples were safranal, isophorone, dihydrooxophorone, but also 4-hydroxy-2,6,6-trimethyl-3-oxocyclohex-1,4-diene-1-carboxaldehyde and 4-hydroxy-2,6,6-trimethylcyclohex-1-enemcarbaldehyde (HTTC). Nevertheless, in the saffron samples studied, 4-hydroxy-2,6,6-trimethyl-3-oxocyclohex-1,4-diene-1-carboxaldehyde (V22) and HTCC (V23) appeared in lower concentrations. HTCC is derived from picroccin, which is also the precursor of safranal and is formed under heat treatment by deglycosylation of picrocroccin or by hydrolysis [39]. Therefore, during the drying process, picrocroccin may produce safranal in high levels, thus producing lower concentrations of HTCC in saffron samples. In summary, saffron from Greece had the highest concentration of total volatile compounds (around 13,067 \(\mu\)g/g) with respect to the Iranian and Spanish saffron samples (around 12,503 \(\mu\)g/g and 11,104 \(\mu\)g/g, respectively). These differences could be related to the geographical origin, which is considered an essential factor in the concentration of volatiles, among others, such as the harvest season, dehydration temperature and duration, and the storage time and conditions [39]. The aroma of saffron is mainly due to the contribution of aldehydes of saffron, such as safranal and its derivative 4-hydroxy-2,6,6-trimethyl-1-cyclohexene 1-carboxaldehyde, but other compounds could contribute as well, with the characteristic saffron aroma developed during the post-harvest treatment. With respect to the odor descriptors, the saffron aroma is especially herbal, spicy, sweet, fresh, woody, floral, and musty, among others (Table 4). Regarding the flower by-products samples from Spain fresh and dried by two different methods (freeze-dried and air oven-dried), 55 volatile compounds were isolated, identified, and quantified (Table 5). The identification parameter of these compounds,namely Kovats index, retention time, chemical family, and odor descriptors, were indicated in Supplementary Table S1. The chemical families more representative found in all samples were: esters (\(n=13\)), aldehydes (\(n=12\)), and acids and alcohols (\(n=5\)). All floral by-product samples presented acetic acid (V1), 2(5H)-furanone (V14), and phenylethyl alcohol (V31). SFL2 (air-oven dried) had the highest concentration of acetic acid (161.55 \(\upmu\)g/g), followed by fresh SFL1 (145.21 \(\upmu\)g/g). The production of this organic acid could occur by the conversion of some carbohydrates in the presence of oxygen.