44%) were the main compounds. Moreover, Brefeldin A ARFs borneol (1.22%) and caryophyllene oxide (1.18%) were the most represented oxygenated monoterpenes and sesquiterpenes, receptively (Tables (Tables22 and and33).Limonene and ��-terpinene levels decreased at semimature stage to 51.81 and 2.53%, respectively. This decrease was accompanied with a concomitant increase of 1,8-cineole (26.43%) and E-��-ocimene (7.93%) levels. The enhancement of the biosynthesis of these compounds suggests an activation of the related synthases at semimature stage. The cyclic monoterpenes including limonene, ��-terpinene, and ��-terpineol are produced from a common intermediate: terpeiyl cation. ��-terpineol undergoes after that cyclisation to lead 1,8-cineole.
On the other hand, the enhancement of the acyclic terpene E-��-ocimene level suggest the activation of E-��-ocimene synthase which derives its conversion from linalyl cation [29]. Shimada et al. [34] reported that the expression of 1,8-cineole and E-��-ocimene genes and their related products in Satsuma mandarin was high in flower and then decreased toward mandarin fruit development. At maturity, 1,8-cineole and E-��-ocimene levels decreased. The essential oil was found to be dominated by limonene (69.00%) followed by ��-terpinene (14.06%). If considering only the mature stage, similar composition has been described by Lota et al. [7] who reported limonene (52.20�C96.20%) and ��-terpinene (tr-36.70%) as the main compounds of French mandarins peel oils.3.3. Antibacterial ActivityThe antibacterial activity of citrus essential oils was tested against human pathogenic bacteria.
The results presented in Table 4 showed great differences in the activity between citrus species and during ripening stages. The oils were effective against Gram (+) and Gram (?) bacteria, with a major activity against S. aureus and E. coli. Bitter orange, lemon, and orange were effective against P. aeruginosa only at maturity while mandarin oil remained inactive against this strain. In accordance with our finding, Espina et al. [12] reported no activity of the peel oil extracted from mature mandarin fruit against P. aeruginosa. On the other hand, lemon and mandarin essential oils extracted from immature fruit exhibited the highest antibacterial activity against E. coli which was comparable of positive control activity. In the case of S.
aureus, the oils were mostly active at mature stage with mandarin oil showing the highest antibacterial activity.Table 4Antibacterial activity of peel essential oils of four cultivars of citrus at different ripening stages against three human pathogenic bacteria.The antimicrobial AV-951 activity of essential oils is believed to be associated with phytochemical components especially monoterpenes [35] which diffuse into and damage cell membrane structures.