[31] analysed the volatiles emitted by the pericarp of unripe and

[31] analysed the volatiles emitted by the pericarp of unripe and ripe Italian lemon fruit and found that limonene level enhanced from 65.30 at immature stage to 68.30% at mature stage. These authors concluded also that the emitted volatiles are originated from glandular download catalog structures which give an essential oil similar to fruit emissions.On the other hand, other representative compounds in lemon oil were ��-terpinene and p-cymene (Table 3) which showed opposite behavior during ripening; in fact, p-cymene level decreased from 9.84% at immature stage to 0.23% at maturity while ��-terpinene level augmented to reach 9.96% at maturity. This is in accordance with their biosynthetic pathway, in which ��-terpinene is a precursor of p-cymene [32]. Further, the Germacrene D and valencene were the most abandon sesquiterpenes (Table 3).

Minor compounds including valencene have stand out in citrus as important flavour and aroma compounds [33].3.2.3. Orange Maltaise Differently to bitter orange and lemon, the peel essential oil of orange fruit extracted at three stages of maturity was mainly dominated by limonene which presented a level of 86.43, 81.52, and 85.35% at immature, semimature, and mature stages, respectively (Table 3). The rest of compounds were weakly represented with levels lower than 1% except for the monoterpenes ��-pinene, camphor and bornyl acetate. These compounds reached their maximum at semimature stage with levels of 1.80, 4.81, and 4.21%, respectively. The increase of camphor and ��-pinene levels suggests an activation of the related terpene synthases which catalyze their formation from the critical intermediates pinyl and bornyl cations, respectively [29].

Concerning sesquiterpenes, ��-humulene (0.16�C0.34%) followed by germacrene-D (tr-0.12%) were found to be the most represented compounds.Our results are in accordance with that of Droby et al. [9] who analysed the composition of peel essential oil of sweet orange Drug_discovery fruit at different stages of maturity and found that limonene was the predominant compound with percentage varying from 72.41 to 94.77%. However, these authors reported a decrease of limonene level during the course of fruit maturity especially at the end of the ripening. Such difference could be attributed to both interactions between genetic (biotic) and environmental (abiotic) factors since in their study, these authors considered ��Valencia�� and not maltaise cultivar.On the other hand, concerning the mature stage, Hosni et al. [15] reported a higher limonene level (96.00%) in the peel essential oil extracted from Tunisian maltaise orange than that obtained in our study. These authors found that ��-pinene was also a marked compound (1.82%). However, camphor was not detected in their samples.3.2.4.

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