Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
8.3.3.3 Literature on MAE
Some interesting results on MAE have recently been published.
For example, the extraction of vanillin from V. planifolia pods using MAE and
ultrasound-assisted extraction has been described. Using absolute ethanol
as the solvent at room temperature, the yield of vanillin was 1.25 wt% at each
of 3 conventional extractions performed over 24 h. Using ultrasound-assisted
extraction, the yield was 0.99 wt%, while it was 1.86 wt% using MAE. These investigations
clearly showed that vanillin extraction by MAE is superior to other
techniques in terms of yield, purity of vanillin, and the time taken to extract
the same percentage of the vanillin from the pods. The extraction of vanillin
and p-hydroxy benzaldehyde (PHB) from vanilla beans using MAE has also
been studied: MAE was superior to the conventional, official method of extraction
in Mexico, which involves maceration of the beans with ethanol for 12 h.
Specifically, extraction time decreased 62-fold and vanillin and PHB concentrations
increased between 40% and 50% with respect to the Mexican extraction
method. This study also showed that extraction of commercial samples was
superior to extraction of dried and lyophilized beans. This observation illustrates
the role played by moisture in aiding extraction, as discussed in Section
8.3.3.2. Several other investigations have shown that MAE has gained
acceptance as a mild and controllable processing tool. MAE is a simple, rapid
and low-solvent-consuming process.
8.3.3.4 Industrial-scale MAE
As mentioned earlier, microwave radiation decays exponentially
inside a solid matrix. This aspect must be carefully weighed while designing
industrial-scale MAE. The major requirements that must be met are:
1. Free distribution of particles allows uniform heating of all the
particles in the solid bed. This criterion also enhances the
extent and probability of proximity of the substrate to the wall
of the sample holder where the microwave exposure is highest.
Most comminuted samples of MAPs which are used for
commercial extraction are not of the same shape and size.
Therefore, there is a strong tendency to “segregate”, which
must be curbed by regular renewal of the layer.
2. Thin and uniform spreading of the substrate layers. This permits
complete and uniform penetration of microwave radiation
even at large water contents.
3. Low depth of the layers. Since microwaves have low penetration
depth (~1.5 cm in H 2 O at 2.45 GHz), the layers should be