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

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.

Optimization of Ultrasound-Assisted Extraction of Flavonoids from Celastrus hindsii Leaves Using Response Surface Methodology and Evaluation of Their Antioxidant and Antitumor Activities

“…is result is in agreement with that for ultrasound-assisted extraction of flavonoids from olive leaves [16] and ultrasound-assisted extraction of polysaccharides from Artemisia selengensis [21]. As shown in Figure 2, the ultrasound-assisted extraction is most effective for flavonoids extraction when the ultrasonic power was at its central level.…”

“…is result is consistent with the ultrasound-assisted extraction of flavonoids from olive leaves [16] and cocoa shells [31], polysaccharides extraction from A. selengensis [21], and the ultrasound-assisted extraction of phenolic from Trapa quadrispinosa [15].…”

“…e TFC is significantly enhanced with the increase in extraction temperature at any extraction time. is was attributed to the positive effect of temperature on the extraction [16,31]. However, a higher temperature caused a reversal of the aforementioned trend.…”

“…At any temperature, the TFC increased when increasing ultrasonic power. is was because a higher ultrasonic power generated a higher cavitation effect, which efficiently broke the plant tissues and cell walls, thus increasing the release of flavonoids into the solvent [16].…”

“…Basically, extraction is the first step in the isolation process to obtain bioactive compounds from biomass materials with its purpose to maximize the content of target compounds for their further utilization. To obtain flavonoids from plant materials, several methods have been applied to enhance extraction efficiency [15,16]. Studies have shown that not only the extraction yield but also the extraction technique is affected by the extracting solvent [17,18].…”