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|Title:||The effect of ultrasound on conventional solvent extraction and supercritical fluid extraction||Authors:||Zhao, Shuna||Keywords:||Hong Kong Polytechnic University -- Dissertations
Ultrasonics in medicine
|Issue Date:||2006||Publisher:||The Hong Kong Polytechnic University||Abstract:||This study evaluated the effect of ultrasound on the extraction yields of active compounds from the herbal materials. Two basic extraction methods were investigated: conventional solvent extraction (CSE) and supercritical fluid extraction (SFE). Results obtained from the extractions with and without ultrasound irradiation were compared. In the study of ultrasound assisted conventional solvent extraction (UAE), saikosaponins from Radix Bupleuri roots were selected as the markers, and different variables including time, temperature, power, particle size, solvent to solid ratio and solvent concentration were tested and the most favorable conditions found as time of 30 min, temperature of 80 ℃, power of 24 W, particle size < 0.3 mm, solvent to solid ratio of 25 ml/g and solvent concentration of 50 %. Compared with CSE, the extraction yields of saikosaponins were facilitated and extraction time was reduced by applying ultrasound. Cavitation was demonstrated to be the major effect in UAE through theoretical calculation and explicit analysis on microscopic images of a scanning electron microscope (SEM). The plant cells disruption, which would not happen in CSE, was found in UAE. Ultrasound promotes the extraction process in two stages: (1) the penetration of solvent into the dry herbal tissues in percolation or maceration processes; (2) the mass diffusion of active compounds from the interior of herbal matrix to the external solvent. In the study of ultrasound effect on SFE, cinnamon oils from the cinnamon barks (dry bark of Cinnamomum cassia presl) were used as the markers. The SFE experiments were carried out by varying factors such as the extraction pressure, temperature, particle size and flow rate of supercritical CO₂and the results were compared with those obtained by the conventional steam distillation (SD). It was found that the cinnamon oil yield by SFE was around four times larger than that by SD. The major constituents obtained by both SFE and SD were similar, while the distributions of individual component varied.
In ultrasound assisted supercritical fluid extraction (UASFE), ultrasound power was also one of the parameters additional to those mentioned in the SFE study. The results from UASFE were compared with those from SFE under the same experimental conditions without the application of ultrasound. It was found that ultrasound improves the yield of cinnamon oils under the similar operating conditions. Theoretical calculations indicated that the phenomenon of cavitation was impossible in UASFE. The optical investigation of SEM showed that the plant cells remained unchanged before and after the experiment of UASFE, which confirmed the calculation results. The Response Surface Methodology (RSM) based on a five level and four factor Central Composite Design (CCD) was employed to obtain the optimum conditions for the UASFE. Based on the simultaneous optimization of oil yield and concentration of cinnamaldehyde and α-copaene, the optimum conditions at pressure of 30 MPa, temperature of 55 ℃, time of 2.5 h, and power of 120 W were obtained and confirmed. A desorption kinetic model was developed for the extraction of cinnamaldehyde from the cinnamon barks using UASFE. By calculating the values of the desorption rate for UASFE, k, which was defined as the release rate of the cinnamaldehyde from the herbal matrix, the extraction curves for UASFE under various conditions were predicted and compared with the experimental data. The model gave a fair prediction on the extraction yield.
|Description:||xxiii, 203 leaves : ill. (some col.) ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P ABCT 2006 Zhao
|URI:||http://hdl.handle.net/10397/3678||Rights:||All rights reserved.|
|Appears in Collections:||Thesis|
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