Extraction of Bioactive Compounds from Olive Leaves

Olive leaves are an agricultural residue resulting from pruning of olive trees and from cleaning of the olive fruit in mills before the oil production. This by-product is underutilized, because it is generally used only as feed for livestock, or crushed together with minor branches from pruning and spread on the soil, or simply burnt. However, the olive leaves could be an important economic resource, as they contain considerable amounts of various bioactive compounds (ubiquitous in plant kingdom or peculiar of the olive tree), which could be extracted and utilized both in foodstuffs and in pharmaceutical industries. In order to evaluate the possibility of the utilization of the olive leaves as a source of valuable compounds, various methods of extraction were investigated, taking in account the recovery and recycle of the solvents and the potential use of the extracted solid residue. In the tests carried out groups of compounds like terpenic acids, chlorophyll and polyphenols were obtained and, among phenolic compounds, oleuropein and flavonoids were further separated. The results of the experiments indicated that the extraction of such compounds from olive leaves produced during pruning of trees or harvesting of olives could be, as well as profitable from an economic point of view, also sustainable for the soil and the environment, provided that this material, devoid of pesticides, is suitably picked, stored and processed by trained personnel, in order to prevent it from being damaged by chemical or enzymatic reactions.