## 3 Discussion  
In this work, a hydroalcoholic solution of _Echinacea purprea_ and propolis was subjected to chemical analysis by SPME-GC-MS to measure the volatile content and by GC-MS of the silylated derivatives to measure the non-volatile one. To the best of our knowledge, this is the first work dealing with the chemical composition of the hydroalcoholic solution of _E. purprea_ and propolis. Until now, the only study regarding this matrix reported the determination of the total content of flavonoids and polyphenols by using the Folin-Ciocalteu and colorimetric assays and the measurement of the antioxidant activity [11]. Some previous works have been conducted on multiple species of _Echinacea_ using different analytical methodologies and, in agreement with our data, phenolic acids represented the more abundant fraction. The content of total phenolics and caffeic acid derivatives in aerial parts and roots of _E. purprea_ grown in China was investigated by HPLC and colorimetric analysis. The results showed that the contents were generally higher in fresh than in dried raw material [12]. Phenolic compounds were determined by TOF-LC/MS in methanolic and aqueous extracts obtained from leaves and flowers of _E. purprea_ and _pullida_. Cichoric acid was the most abundant in the methanolic extracts of both species, but not in the aqueous ones, where caffeic acid prevailed, although in small quantities [13]. Ethanol extracts of _E. angusifolia_ DC roots from different natural geographic areas were investigated by HPLC. The results highlighted a trend of caffeic acid and its derivatives, which contributed to differentiating the investigated chemotypes [14]. Regarding propolis, its chemical composition varies according to different factors such as the season, the climate, the hive and the geographical area of the honey [15; 16]. Consequently, multiple compositional profiles have been described. In general, the main components were phenolic compounds, especially cinnamic acid derivatives and flavonoids, but also amino acids and amines [17; 18]. By LC-MS technique, the phenolic compounds content of 19 propolis samples from 17 beekeepers of 5 Finnish provenances, was measured. The compounds found in the largest quantities were methyl-naringenin and caffeic acid phenethyl ester [19]. [PERSON] et al. [20] investigated ten propolis samples from Bulgaria, Italy and Switzerland by GC-MS. The results showed how the compositions of the one of Swiss origin, rich in phenolic glycerides, and the Sicilian one, rich in ditergenic acids, differed considerably from the others [20]. However, despite this variability in phytochemical composition, propolis has general pharmacological value [21]. Concerning the antimicrobial properties, the EAP solution displayed a strong effectiveness, which affected the bacterial growth capability over time. Moreover, it is worthy of consideration that the antimicrobial effect was exerted not only on type strains and food isolates but also on pathogenic isolates. In addition, Gram negative bacteria generally show higher resistance to antimicrobial compounds because of the composition of their cell wall, but in our case, no differences in terms of sensitivity to EAP were observed, with the only exception of _Pseudomonas aeruginosa_ ATCC 27853 (strain S7). The molecular complex that characterizes the EAP solution could exert the relevant bioactivity. [PERSON] et al. [22]