Effect of electric field on mass transfer during oleuropein extraction

Abstract

The use of alternative extraction methods has increased since conventional methods have disadvantages like long processing time and limited extraction yield. It is known that the extraction yield is enhanced, and the processing time is shortened by the electric field. However, the mathematical characterization of the electrically assisted processes is needed for a better understanding and the improvement of extraction. In this study, effects of the moderate electric field extraction (MEF-E) parameters (frequencies of 1, 1000, and 2000 Hz, and wave types of sine and square) on yield, cell disintegration index (Zc), microstructure, and mass transfer coefficient (Deff) were investigated to examine mass transfer characteristics of the extraction of oleuropein from olive leaves. Correlation analysis was performed to investigate the relations between yield, Zc, Deff, and the changes in the cross section areas of palisade cells. The frequency and wave significantly affected yield, Zc, microstructural changes, and Deff values (p < 0.05). Additionally, the Zc value showed a good correlation with yield, microstructure, and Deff in both sine and square waves (p < 0.05). It was concluded that the extraction level and microstructural changes could be controlled by Zc during the MEF-E process. Two different finite element models (model 1: fixed Deff and model 2: Deff depending on the Zc) were used for mass transfer, and model 2 gave better predictions (p < 0.05). Thus, it will be possible to characterize and monitor oleuropein transfer depending on the effects of frequency and wave type applications during the MEF process. The model consisting of the Zc–Deff relationship showed that the use of Zc would be preferred for the characterization of mass transfer rather than calculating the Deff value. It is thought that the effects of electric field parameters on microstructure with the developed models will be determined and successfully characterized, thus contributing to the understanding of the effects of electric field extraction processes on mass transfer. However, it is recommended that similar studies are conducted for other plants in order to develop a valid approach on the extraction process from plants.