Comparative Evaluation of the Phytochemical Profiles and Antioxidant Potentials of Olive Leaves from 32 Cultivars Grown in China

Abstract

Olives (Olea europaea L.) are a significant part of the agroindustry in China. Olive leaves, the most abundant by-products of the olive and olive oil industry, contain bioactive compounds that are beneficial to human health. The purpose of this study was to evaluate the phytochemical profiles and antioxidant capacities of olive leaves from 32 cultivars grown in China. A total of 32 phytochemical compounds were identified using high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry, including 17 flavonoids, five iridoids, two hydroxycinnamic acids, six triterpenic acids, one simple phenol, and one coumarin. Specifically, olive leaves were found to be excellent sources of flavonoids (4.92–18.29 mg/g dw), iridoids (5.75–33.73 mg/g dw), and triterpenic acids (15.72–35.75 mg/g dw), and considerable variations in phytochemical content were detected among the different cultivars. All tested cultivars were classified into three categories according to their oil contents for further comparative phytochemicals assessment. Principal component analysis indicated that the investigated olive cultivars could be distinguished based upon their phytochemical profiles and antioxidant capacities. The olive leaves obtained from the low-oil-content (<16%) cultivars exhibited higher levels of glycosylated flavonoids and iridoids, while those obtained from high-oil-content (>20%) cultivars contained mainly triterpenic acids in their compositions. Correspondingly, the low-oil-content cultivars (OL3, Frantoio selection and OL14, Huaou 5) exhibited the highest ABTS antioxidant activities (758.01 ± 16.54 and 710.64 ± 14.58 mg TE/g dw, respectively), and OL9 (Olea europaea subsp. Cuspidata isolate Yunnan) and OL3 exhibited the highest ferric reducing/antioxidant power assay values (1228.29 ± 23.95 mg TE/g dw and 1099.99 ± 14.30 mg TE/g dw, respectively). The results from this study may be beneficial to the comprehensive evaluation and utilization of bioactive compounds in olive leaves.

Changes in Phytochemical Profiles and Biological Activity of Olive Leaves Treated by Two Drying Methods

“…Furthermore, as reported by Lachowicz et al ( 44 ), the initial chemical compositions of different saskatoon berry cultivars potentially influenced the alterations of the polyphenolic compounds during convective drying. Therefore, these inconsistent results might also be correlated with the used cultivars, as the phytochemical compounds in the olive leaves differed among the different cultivars ( 45 ). Moreover, ultrasound-assisted extraction was employed to recover the phenolic compounds in this study, which potentially influenced phenolic extraction ( 30 ).…”

Comparative metabolic profiling of olive leaf extracts from twelve different cultivars collected in both fruiting and flowering seasons

“…It showed a UV absorption maximum at 345 nm for band I characteristic for flavones. The EIC at m/z 447.11 with its strong fragment at m/z 285, due to the loss of a hexose residue, indicates luteolin-O-hexoside (22). Luteolin-7-O-glucoside was previously detected as a major compound in olive leaf extracts as well as in the fruits 17 .…”

Nocellara Del Belice (Olea europaea L. Cultivar): Leaf Extract Concentrated in Phenolic Compounds and Its Anti-Inflammatory and Radical Scavenging Activity

“…Both the acetone-water and the hydroalcoholic extracts showed a content of luteolin-7-O-glucoside in the range of some Spanish, Croatians cultivars growing in Morocco, as well as for a Nocellara del Belice cv. growing in China [ 53 , 54 , 61 , 62 ] and in line with Benincasa et al [ 63 ], who investigated the leaf extract of the most common variety of Calabrian cultivars. Based on the higher level of phytochemical compounds in acetone-water leaf extract from Nocellara del Belice cv., a dry extract, rich in phenolic compounds, has been obtained, using a polystyrene resin.…”

“…the oleuropein level, in the leaves harvested in June, is comparable with the levels observed in our study, although the solvents used for the extraction were different [ 35 ]. In addition, the hydroalcoholic (50%, v / v ) extract from Nocellara contained oleuropein within the literature-reported range [ 53 , 54 ]. Unexpectedly, the lowest content of oleuropein was determined in Carolea cv., with the extract obtained using EtOH-water, although Nicolì et al [ 55 ], reported higher level of the secoiridoid in the same cultivar.…”