Comprehensive Research on Essential Oil and Phenolic Variation in Different Foeniculum vulgare Populations During Transition from Vegetative to Reproductive Stage

Chemical composition and antioxidant activity of four fennel populations (England, Spain, Poland and Iran) were investigated during six developmental stages including two vegetative and four reproductive phases. In reproductive phase, the essential oil content of fruits decreased and the maximum content (5.9%) was obtained in immediate fruits. The essential oils were analyzed using GC/MS. trans-Anethole was the main component of the leaves and the fruits oil. In leaves, it ranged from 41.28% in England at late vegetative stage to 56.6% in Poland population at early vegetative stage. Other major compounds of leaves were limonene, α-pinene and (Z)-β-ocimene. In reproductive phases the trans-anethole increased dramatically. It varied from 85.25% in immature fruits from Poland to 90.7% in pre-mature stage from Spain. The highest phenolic content in the extracts at different growth stages obtained 189 mg TAE/g DW at full mature stage of seed in Iran population. The flavonoid of leaves extract ranged from 3 to 7.5 mg QUE/g DW, while in fruits extract varied from 3 to 10.3 mg QUE/g DW. Antioxidant activity of the extracts was evaluated using 1,1-diphenyl-2-picrylhydrazy (DPPH) and β-carotene model systems. Immature and full mature growth stages of fennel population from Spain indicated the highest activity in quenching of DPPH radical (74.2% and 74.5, respectively). Antioxidant activities of the extracts had high positive correlation with their phenolic contents in all fruit maturity stages. Finally, it might probably be suggested that in fennel the hot and humid condition can lead to increase trans-anethole, while the hot and dry one can produce higher amount of phenolics and flavonoids.