Kinetic and compositional study of phenolic extraction from olive leaves (var. Serrana) by using power ultrasound

Power ultrasound is being used as a novel technique for process intensification. In this study, the feasibility of using power ultrasound to improve the phenolic extraction from olive leaves was approached taking both compositional and kinetic issues into account and also determining the influence of the main process parameters (the electric power supplied, emitter surface and temperature). For this purpose, the extraction kinetics were monitored by measuring the total phenolic content and antioxidant capacity and mathematically described by Naik's model, and HPLC–DAD/MS–MS was used to identify and quantify the main polyphenols. 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.Industrial relevanceOlive 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.

► The use of ultrasound in the phenolic extraction from olive leaves was addressed.
► The ultrasound effectiveness depended on the effective power applied to the medium.
► Ultrasound assisted extraction shortened the extraction time from 24 h to 15 min.
► The application of ultrasound did not modify the composition of olive leaf extracts.