Health properties of olive leaves
They contain considerable amounts of various bioactive compounds, which could be extracted and utilized both in foodstuffs and in pharmaceutical industries
Olive (Olea europaea) leaves are used as anti-rheumatic, anti-inflammatory, antinociceptive, antipyretic, vasodilatory, hypotensive, antidiuretic and hypoglycemic agents in traditional medicine. Recently, it has been shown that olive leaf extract (OLE) has calcium channel blocker property; however, its influences on nociceptive threshold and morphine effects have not yet been clarified.
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.
Total flavonoid and phenolic contents were significantly higher in the 80% ethanol extract, butanol, and ethylacetate fractions than hexane, chloroform and water fractions. Oleuropein was identified as a major phenolic compound with considerable contents in these major three fractions and the extract that correlated with their higher antioxidant and radical scavenging.
Power ultrasound is being used as a novel technique for process intensification. The extraction kinetics could be monitored by measuring the total phenolic content and antioxidant capacity. The electric power supplied and the emitter surface greatly affected the effective ultrasonic power applied to the medium, and hence the extraction rate. However, the influence of temperature on ultrasound assisted extraction was not clear. Compared with conventional extraction, ultrasound assisted extraction reduced the extraction time from 24 h to 15 min and did not modify the extract composition.
Olive crop produces a significant quantity of byproducts (leaves, branches, solid and liquid wastes), coming from the tree pruning, fruit harvest and oil production, which are rich in phenolic compounds with bioactive properties. The extraction of the bioactive compounds could be an interesting option with which to increase the value of these byproducts, as it requires efficient extraction techniques in order to reduce processing costs and improve productivity. In this sense, ultrasound assisted extraction is considered a novel technique used as a means of intensifying a slow process, such as the leaching of polyphenols from vegetable matrices. In order to further address the industrial applications of ultrasound assisted extraction, a kinetic study should be carried out determining both the effective energy introduced into the medium, as well as its influence on the extract quality.