3.1. Identification of phenolic com

3.1. Identification of phenolic compounds, determination
of total flavones and total polyphenols in OLE and OFE, and
bound phenolics in olive leaf and fruit
The phenolic contents of OLE and OFE were calculated based
on the corresponding standard concentration–response curves
obtained through HPLC (Fig. 1 and Table 1).Ten phenolic compounds
belonging to four main groups were identified in OLE
and OFE: oleuropeosides (oleuropein and verbascoside), flavonols
(rutin), flavones (luteolin-7-glucoside, apigenin-7-
glucoside and luteolin) and substituted phenols (hydroxytyrosol,
vanillin, vanillic acid and caffeic acid). Oleuropein (6.53 mg/g)
was detected at the highest concentration in OLE, followed by
caffeic acid (2.71 mg/g) and verbascoside (0.83 mg/mL).The other
phenolics were present in trace amounts. These observations
agree with the findings reported by Pereira et al. (2007). The
differences in the reported OLE phenolic compositions are likely
due to the different methodologies used and the specimen
origins (Hayes, Allen, Brunton, O’Grady, & Kerry, 2011). All of
the phenolics detected in OFE, particularly oleuropein
(0.0424 mg/g), were found at lower concentrations less than in
OLE, similar to the findings reported by Del Río, Báidez, Botía,
and Ortuño (2003).Two predominant compounds in OFE were
caffeic acid (0.081 mg/g) and luteolin (0.081 mg/g), and these
were followed by hydroxytyrosol (0.076 mg/g), vanillin (0.072 mg/
g) and apigenin-7-β-D-glucose (0.018 mg/g). The other
substituent phenols (vanillic acid, verbascoside, luteolin-7-β-
D-glucose and rutin) were found at low levels (≤0.01 mg/g).
This observation of higher polyphenolics in OLE than that
in OFE was similar to the findings reached by Teleszko and
Wojdyło (2015), who proved that the polyphenolic content (particularly
for phenolic acids and flavonols) in the leaf was
significantly higher than that in their fruit within the seven
selected species, e.g., apple, quince, Japanese quince, chokeberry,
cranberry, blackcurrant and bilberry. The differences in
the content of polyphenolic compounds between different morphological
parts of plants resulted from the specific species.
Actually, they suggested that the synthesis of polyphenolic compounds
in plants depends on the degree of sunlight exposure
and water relations during the vegetation period. Based on it,
the olive leaf probably gets more sunlight exposure and water
than the olive fruit. In addition, Tattini et al. (2004) found an
interesting phenomenon that the Ligustrum vulgare leaves from
the shaded side of a bush (light exposure 6%) contained 3-fold
less polyphenols than those grown under full sunlight exposure
(100%).With this, the degree of plant maturity depends