Eco-Friendly Extraction of Olive Leaf Phenolics and Terpenes: A Comparative Performance Analysis Against Conventional Methods

The present study focuses on recovering phenolic compounds and terpenes from olive leaves, which are generated as by-products during olive oil processing. To this end, conventional extraction/maceration (CE) and advanced extraction techniques such as subcritical water extraction (SWE), pressurized fluid extraction (PLE) and ultrasound-assisted extraction (UAE) were employed to compare and determine the most effective procedure. The phenolic and terpenoid composition of the extracts revealed a total of 33 compounds in HPLC-QTOF-MS analysis. According to these findings, the optimal extraction techniques for the maximum recovery of secoiridoids from olive leaves were PLE and UAE, with no significant difference between them (21.9891 ± 2.5521 mg/g DW and 21.0888 ± 1.3494 mg/g DW, respectively). Regarding to flavonoids, UAE was the most effective extraction technique, yielding 4.9837 ± 0.6739 mg/g DW. However, SWE recovered the highest amount of phenolic alcohols (7.4201 ± 0.9848 mg/g DW), which could be due to degradation of the secoiridoids during extraction. Conversely, UAE was more successful than the other techniques for the extraction of the terpene family (0.7373 ± 0.0601 mg/g DW). The present study therefore focuses on comparing different extraction techniques for revalorizing olive leaves as a source of bioactive compounds, specifically polyphenols and terpenes, due to their beneficial health properties.