Effects of fruit maturity and drying on extraction yields and densities of essential oils from fresh zest of Citrus limon Eureka

Content of essential oils (EOs) obtained by a 3-h hydrodistillation of fresh and dried zests of Tunisian Citrus limon, Eureka variety, harvested on the same tree at two maturity stages was compared. EO extraction yield expressed as fresh weight was decreased from 1.62 ± 0.11% for immature green fruits (w/w^f: weight EO/weight fresh zest) for immature green fruits up to 0.87 ± 0.04% for zests of fully ripped fruits. Drying fresh zests in the oven at 50 °C for 1, 3 or 7 h reduced weight by 25.2 ± 7.5%, 53.5 ± 8.5% and 73.4 ± 0.06%, respectively. These weight changes attributed to moisture losses were associated with a maximal EO loss of 73.9 ± 6.7% already after 1-h drying and significantly increased EO densities. As a consequence, extraction yields of 0.32–0.42% (w/w^f) for EO from fresh zests of unripe fruits significantly increased up to 0.55 ± 0.08% (w/w^d), 0.81 ± 0.15% and 1.44 ± 0.32 when expressed as dried zest weight after 1-, 3- and 7-h drying, respectively. This balanced study demonstrates for the first time that 80% of Citrus limon zests EOs are lost during the drying process.