Optimization of Ultrasound-Assisted Extraction of Flavonoids from Olive (Olea europaea) Leaves, and Evaluation of Their Antioxidant and Anticancer Activities

Bixia Wang,Siyuan Luo,Jinqiu Liao,Tian Li,Shiling Feng,Yan Huang,Ruiwu Yang,Ming Yuan,Chunbang Ding,Jipeng Qu

doi:10.3390/molecules23102513

Bixia Wang, Siyuan Luo + Show 8 more

Open Access

https://doi.org/10.3390/molecules23102513

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Abstract

Olea europaea leaves are the major byproduct of olive farming. In this study, ultrasound-assisted extraction of flavonoids from olive leaves was optimized using response surface methodology, and the flavonoid compounds and their antioxidant and anticancer activities were investigated by high performance liquid chromatography. The results showed that the optimized conditions for achieving the maximum yield of flavonoids (74.95 mg RE/g dm) were 50 °C temperature, 270 W power, 50 min time, and 41 mL/g liquid-solid ratio. There was a significant difference in the total flavonoid content between the aged and young leaves harvested in April and July, and six main components were quantified. Among them, luteolin-4’-O-glucoside was the most predominant flavonoid compound, followed by apigenin-7-O-glucoside and rutin. Olive leaves also contained small amounts of luteolin, apigenin, and quercetin. Additionally, excellent antioxidant activity was exhibited when tested with the DPPH assay; superoxide radical-scavenging ability and reducing power was also tested. The anticancer activity of the flavonoids was assessed using HeLa cervical cancer cells, and it was observed that increasing concentrations of olive leaf flavonoids resulted in decreased cancer cell viability. These results suggest that the flavonoids from olive leaves could be used as a potential source of natural antioxidants for the pharmaceutical and food industries.

Highlights

Olea europaea L., an evergreen tree belonging to the Oleaceae family, is widely distributed in many Mediterranean countries [1]
The results showed that the total flavonoid content in April was aged leaves, followed by young leaves (58.17 mg routine equivalents (RE)/g dm)
A similar result was found in a study by Nadeem, Ubaid, Qureshi, Munir and Mehmood [14], which demonstrated that the increase of flavonoids from juice blends could enhance their antioxidant activity. These results indicated that Apr.AL with higher reducing power might possess higher amounts of total flavonoid content 2018

Summary

Introduction

Olea europaea L., an evergreen tree belonging to the Oleaceae family, is widely distributed in many Mediterranean countries [1]. Olive trees were introduced to China in 1956 as an important economic crop, and thereafter, they were widely cultivated along the Jinsha River in the hot, arid valley [2]. A huge quantity of olive leaves is generated as an agricultural byproduct of the olive oil industry and accumulates during pruning [3]. Almost 600,000 tons of olive leaves are produced annually in China [4]. These byproducts are burned or directly discarded, causing environmental pollution and waste of a resource.

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