Medicinal Plants Classification Biosynthesis and ... - Index of

Quality Control of Polysaccharides from Medicinal Plants and Fungi
2. Isolation and Fraction of Polysaccharides
Plant and fungal cell walls are primarily polysaccharide in composition. Selection of an
extraction method, the first and usually the most important process for quality control,
depends on the cell wall structure. Hot water extraction has been a popular approach. In
general, the extraction method involves elimination of low molecular substances from sample
material with a certain organic solvent, followed by the extraction with water (100 o C) for
certain time. This extraction yielded water-soluble polysaccharides. The parameters such as
extraction time, solid/liquid ratio, immersing time and extraction temperature were studied to
optimize the polysaccharides extraction using uniform design [6]. Actually, the extraction
method can be varied based on the structure and water-solubility of polysaccharides, but the
basic rule is to break the cell wall from outer layer to the inner layer with mild-to-strong
extraction conditions (pH and temperature). Therefore, alkali solutions are usually used for
extraction of acidic polysaccharides which are insoluble in hot water [7-10]. It has also been
noted that hot-water extraction of polysaccharides is associated with long extraction time and
high temperature. Therefore, it is desirable to find a method for economical and efficient
extraction of polysaccharides. The advantages of ultrasonication treatments during the
extraction of polysaccharides have been documented for various types of plant tissues [11-
14]. However, the high extraction efficiency of ultrasonication is spotted because it may
degrade some polysaccharides [15].
Pulsed electric field electro-technology (PEF) is an emerging technology in the field of
food preservation, which is based on a pulsing power delivered to the product placed between
a set of electrodes that confine the treatment gap of the PEF chamber [16]. Under the process
of PEF, the differential electric pressure between the cell interior and the exterior of cell
membranes is so large that it will lead to rapid permeation. Consequently, the concentration
between the cell interior and the exterior of cell membranes can reach equilibrium in an
ultrashort time. PEF has been used for the extraction of active ingredients such as
polysaccharides from natural biomaterial at room temperature without any heating process
[17]. The result showed that the largest extraction ratio is 55.59% by PEF on the conditions
of 0.5% KOH, 20 kV/cm electric field intensity and 6 μs pulse duration. Comparing it with
the conventional extraction methods, such as alkali extraction method, enzyme extraction
method and compound extraction method, the extraction ratio and polysaccharide content of
PEF method are higher than the other three methods, while the impurity of extraction
material is less. So the PEF method is a novel and promising method to extract
polysaccharide, which will be beneficial to the food and drug industries.
Extracted polysaccharides can be further fractionized and purified using a combination of
techniques, such as precipitation (ethanol, fractional and acidic precipitation), ultrafiltration,
gel filtration, ion-exchange chromatography and affinity chromatography. The separation of
water soluble and insoluble polysaccharide can be achieved by successive extraction of raw
material with hot water and different alkaline solutions. The impurities of hot water extract
are excluded using ethanol precipitation. Then the separation of acidic and neutral
polysaccharides can be achieved by anion-exchange chromatography. The neutral
polysaccharide in the mixture is first eluted by an appropriate running buffer; the acidic
polysaccharide is then eluted at a higher salt concentration. Different molecular sizes of
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