Ultrasonic vs. Microwave Extraction Intensification 1
globe-instruments.com / 2016-11-03

Ultrasonic vs. Microwave Extraction Intensification of  Active Principles from Medicinal Plants


Ani Alupului1*, Ioan Calinescu2, Vasile Lavric1


1University Politehnica of Bucharest, Chemical Engineering Department


RO-011061, Polizu 1-7, Bucharest, Romania


2University Politehnica of Bucharest, Organic and Macromolecular Compounds


Technology Department






Microwave  and ultrasonic  fields,  biochemically safe,  were  used to  extract  stevioside


glycosides  from   Stevia  rebaudiana   Bert.  Distilled  water   in  1/10   (w/v)  ratio   was


employed as solvent. The  active principle was quantified by HPLC. A  comparison with


classical extraction results is provided.


Both  intensive  extraction  techniques of  active  compounds  seem  to  be economically


promising (simple and efficient), still care must be taken to avoid local over-exposure.





 Microwave  and ultrasonic  fields,  biochemically safe,  were  used to  extract  stevioside glycosides  from   Stevia  rebaudiana   Bert.  Distilled  water   in  1/10   (w/v)  ratio   was employed as solvent. The  active principle was quantified by HPLC. A  comparison with classical extraction results is provided.

Both  intensive  extraction  techniques of  active  compounds  seem  to  be economically promising (simple and efficient), still care must be taken to avoid local over-exposure.


Keywords: Ultrasound assisted  extraction, Microwave extraction, Stevioside  glycoside, Medicinal plants.


1. Introduction


Stevia  rebaudiana, native  from  Paraguay, is  used  as herbal  sweetener  for over  1500 years.  Extracts of  Stevia  rebaudiana  are part  in  weight-loss  programs because  of  its ability to  reduce the  cravings for  sweet and fatty  foods, to  treat the  diseases diabetes, hypoglycaemia, candidasis,  high blood  pressure,  skin abrasions  and inhibiting  growth and  reproduction  of  bacteria-like   plaque.  

Stevia's  greatest  appears  to  be   a  natural alternative  to   artificial  sweeteners  (such   as  aspartame   or  sodium  saccharin).   The sweetness  in  Stevia  rebaudiana  is   mainly  attributed  to  two  glycoside  compounds: stevioside (3-10%  of dry  leaf weight)  and rebaudioside  A (1-3%) which  can be  up to 250  times  sweeter  than sucrose  (Duke,  2006).  The  glycosides  of  Stevia  rebaudiana

leaves have been extracted using  classical techniques: maceration or thermal extraction, either  requiring  long  processing time  and  low  efficiency,  in  case  of  maceration, or facing thermal degradation, in case of infusion and decoction (Vinatoru, 2001).

In order  to increase  the  productivity, several  intensification techniques  like ultrasonic waves,  supercritical fluids  or  microwaves  were  associated with  extraction  of  plant’s compounds to improve  the yield and quality of  extracted products (Wang, 2006). From these,  ultrasound   assisted   and  microwave   extractions  emerged   as  two   promising

techniques from  an economical point  of view, being  inexpensive, simple and  efficient.



These procedures increase at least one of the major parameters governing extraction: the kinetic, through  the partial mass  transfer rates, the  interfacial area  or the driving  force (Cravotto, 2008).

Ultrasound waves  were employed to  extract active  compounds such saponins,  steroids and  triterpenoids from  Chresta spp.  about three  times  faster than  with the  traditional extraction methods (Schinor et al., 2004).

The  ultrasonic  field   enables  generation,  locally,  of  micro-cavitations   in  the  liquid surrounding  the plant  material. The  effects are  twofold:  mechanical disruption  of the cell’s wall  releasing  its content  and local  heating of  the liquid,  increasing the  extract diffusion.  The kinetic  energy is introduced in the  whole volume following the collapse of  cavitation bubbles  at or  near  walls or  interfaces  thus improving  the  mass transfer across the solid-liquid interface.  The mechanical effects of ultrasounds  induce a greater penetration of solvent into  cellular membranes walls, facilitating the release  of contents of the cells and improve mass transfer (Kiel, 2007).



The   applications  of   microwave   assisted   extraction   to   natural   compounds   such glycosides,   alkaloids,  carotenoids,   terpenes,   essential   oils  has   been   reviewed  in (Kaufmann, 2002).



The  use  of   microwave  energy  for  the   extraction  of  active  substances   from  plant materials  results  in  more  effective  heating,  faster  energy  transfer,   reduced  thermal gradients, selective heating,  reduced equipment size,  faster response to process  heating control, faster  start-up  and increased  production. During  absorption,  the microwaves’  energy  is  converted  into  kinetic  energy,  thus  enabling  the  selective  heating  of  the microwave-absorbent  parts  of the  plant  material.  The  volume  increased in  this  way makes cells explode, releasing their content into the liquid phase. When  the liquid phase absorbs   the   microwaves,    the   kinetic   energy    of   its   molecules    increases,   and consequently, the diffusion rate increases too (Mandal, 2007).



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