Comparative analyses of diffusion coefficients for different extraction processes from thyme

Slobodan Petrovic, Jasna Ivanovic, Stoja Milovanovic, Irena Zizovic
2012 Journal of the Serbian Chemical Society  
This work was aimed at analyzing the kinetics and mass transfer phenomena for different extraction processes from thyme (Thymus vulgaris L.) leaves. Different extraction processes with ethanol were studied, i.e., Soxhlet extraction and ultrasound-assisted batch extraction on the laboratory scale, as well as pilot plant batch extraction with mixing. The extraction processes with ethanol were compared to the process of supercritical carbon dioxide extraction performed at 10 MPa and 40 °C. The
more » ... and 40 °C. The experimental data were analyzed by a mathematical model derived from the Fick's second law to determine and compare the diffusion coefficients in the periods of constant and decreasing extraction rates. In the fast extraction period, the values of the diffusion coefficients were one to three orders of magnitude higher compared to those determined for the period of slow extraction. The highest diffusion coefficient was recorded for the fast extraction period of supercritical fluid extraction. In the cases of the extraction processes with ethanol, ultrasound, stirring and increasing extraction temperature enhanced the mass transfer rate in the washing phase. On the other hand, ultrasound contributed the most to the increase of mass transfer rate in the period of slow extraction. Copyright (CC) SCS 800 PETROVIĆ et al. value of this crop worldwide. 1,2 In recent investigations, thyme was identified as a valuable raw material for the production of antibacterial agents, whereby thyme isolates showed stronger antibacterial activity than those of sage and rosemary. 3 Nowadays, different extraction techniques have been widely investigated and applied to obtain valuable natural compounds from plant material for commercial application in the food, pharmaceutical and cosmetic industries. 4 Steam distillation is an appropriate technique for the isolation of volatile components from plant materials, such as essential oils, some amines and organic acids, as well as other, relatively volatile compounds, insoluble in water. Since it is performed at elevated temperature, it requires substantial energy consumption and may cause thermal decomposition of the components of the essential oil, resulting in flavour changes. 5 Extraction with organic solvents or water is used for the isolation of thermolabile substances from plant materials. The organic solvents are removed from the extracts by evaporation under vacuum to obtain concretes which are further subjected to degreasing with ethanol to obtain essential oils for application in the cosmetic and perfumery industries. Processes of extraction with organic solvents are limited by the compound solubility in the specific solvent used, and hence the quality and quantity of the extracted mixture are determined by the type of extractant applied. 4 Solvent extraction in a Soxhlet apparatus enables the isolation and enrichment of compounds of medium and low volatility and thermal stability. It allows a high recovery, but has a number of shortcomings, such as long extraction times, large consumption of solvents, cooling water and electric energy and often unsatisfactory reproducibility. 6 These shortcomings have led to the consideration of the use of new so-called "green" separation techniques with shortened extraction time, reduced organic solvent consumption, and increased pollution prevention, such as microwave extraction, supercritical fluid extraction, ultrasound extraction, ultrafiltration, flash distillation, the controlled pressure drop process and sub-critical water extraction. Nowadays, extraction processes for the isolation of phytochemicals under extreme or non-classical conditions are constantly being developed in applied research and industry.7,8 Ultrasound-assisted extraction (USE) is considered as an emerging potential technology that could improve heat and mass transfer of the solutes and increase the efficiency of the isolation of bioactive principles from plant materials. Ultrasound waves produce a cavitational effect that facilitates the erosion of the solute from the interfacial surfaces of a plant material and the release of the extractable compounds by disrupting the plant cell walls. 6, 7, 9, 10 The USE process thus enables high reproducibility along with a reduction of the solvent consumption and extraction time. Several classes of food components, such as aromas, pigments, antioxidants, and other organic and mineral compounds, have been efficiently isolated by a USE process from a variety of matrices (mainly animal tissues, food and plant materials). 7 Scanning electron micrographs have provided evidence of
doi:10.2298/jsc110616009p fatcat:x6hucbcwjfa7lgicqjnwpzq2eq