Analysis of the spontaneous volatile emission of different aerial parts of caper (Capparis spinosa L.)

Capparis spinosa L. is a perennial eremophyte shrub, widely distributed in Mediterranean Europe: in Italy it is commonly found as a ruderal species growing on and covering walls of the cities. Its highly developed root and xylem systems are the reason of its ability to survive in both cold and heat stressed environments, as they confer the plant the capability of using the groundwater resources (Yin et al., 2014) and the ability of growing on very dry spots, like walls and rocky coastal areas (Kulisic-Bilusic et al., 2010). We analysed the spontaneous volatile emission of different aerial parts of caper (Capparis spinosa L.) by means of HS-SPME-GC/MS. The samples included leaves, buds, sepals, seeds, fruits, pistils, stamens, petals and flowers; they were randomly collected from specimens growing as wild, ruderal plants on the medieval walls of Pisa (Italy). We identified 178 different compounds of which, in different proportion based on the type of sample, the main ones were (E)-β-ocimene, methyl benzoate, linalool, β-caryophyllene, α- guaiene, germacrene D, bicyclogermacrene, germacrene B, (E)-nerolidol, isopropyl tetradecanoate and hexahydrofarnesyl acetone. We carried the multivariate statistical analysis of the results, with both the HCA (Hierarchical Cluster Analysis) and PCA (Principal Component Analysis) method. The analyses seem to point out that the parameter leading the emission patterns is the function of the studied sample: the flowers samples showed differences in the emission profile between their fertile and sterile portion, and between the other parts of the plant. The green parts emission profiles group them together in a cluster of their own and they are different from those of seeds and fruits. Furthermore, we hydrodistilled caper fully bloomed flowers and analysed its composition. Literature reports analyses of the essential oil of caper seeds (Ara et al., 2014; Yin et al., 2014), fruits (Afsharypuor et al., 1998; Yin et al., 2014), roots (Afsharypuor et al., 1998), leaves (Afsharypuor et al., 1998) and floral buds (Kulisic-Bilusic et al., 2010). The bloomed flowers essential oil volatile profile significantly differs from those of the essential oils obtained from other parts of Capparis spinosa reported in the literature: it is the only volatile oil rich in oxygenated sesquiterpenes (mainly (E)-nerolidol and (E)-nerolidol acetate) and oxygenated monoterpenes (mainly linalool).