HPLC method indicate that our method is appropriate for the goals
of this study, in terms of selectivity, accuracy, precision in a wide
scope of natural compound analysis. Quantitative results of bark
covered by rhytidome or periderm and leaf (g/100 g dry matter)
are summarized in Table 3.
These results show that all of the three extracts are rich in phenolics
but their composition is different. Comparative composition
of these tissues shows that rhytidome-covered bark contains the
highest amounts of the hydroxycoumarin esculetin (3.01%), the
cinnamic acid derivative acteoside (1.72%) and acteoside isomers
(1.56%), whereas the amounts of these compounds in periderm
are significantly lower. In accordance to the literature data, leaf
was found to contain extraordinarily high amount (8.52%) of the
secoiridoid oleuropein. Additionally, the oleuropein contents measured
in bark samples – especially in periderm (4.98%) – could
also be regarded as considerable amounts. Concerning other secoiridoids,
oleoside and secologanoside were found also significant
in periderm; however they were not quantified. Some differences
in flavonoid composition can also be observed. Leaf has a higher
luteolin and luteolin-hexoside content while rhytidome is rich in
naringenin.
These differences in the phenolic composition also indicate the
potential role of phenolics in the plant physiology. Because of the
high level of secoiridoids (oleuropein, oleoside and secologanoside)
measured in younger organs, such as leaf and periderm-covered
bark, these compounds can play a role in the growth and development
of olive (Amiot et al., 1986). However, esculetin and acteoside
along with its isomers may have a protective role (e.g., DNA protection)
in the plant therefore they accumulate in older tissues, like
the rhytidome-covered bark (Korkina, 2007).
4. Conclusions
Phenolics in the methanolic extracts of O. europaea rhytidome,
periderm and leaves were identified and quantified by online
chromatographic methods. In total, 41 compounds were detected;
many of them were identified for the first time in olive tissues.
Based on quantitative data it can be stated that both types of
olive bark are rich and distinctive resources of particular phenolic
compounds. These results offer a firm dataset for compoundselective
development of medicinal, health-care, cosmetic and
culinary products of natural olive origin.