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After extracting polysaccharides using a low eutectic solvent (DES, Deep Eutectic Solvent), the removal of the solvent is a crucial step. The following are common methods for solvent removal and their specific procedures:
1. Water dilution + dialysis method Applicable scenarios
The DES components have strong hydrophilicity (such as chlorocitrate-urea, glycol-based DES). Step
1. Dilution: Dilute the extract with deionized water (volume ratio 1:5 to 1:10) to reduce the viscosity of DES.
2. Dialysis: Place the solution in a dialysis bag (with a molecular weight cut-off of 3.5 - 14 kDa). Perform continuous dialysis with running water for 24 - 48 hours (or replace the water 4 - 6 times) until there is no DES component in the dialysate (this can be monitored by HPLC or conductivity).
3. Concentration: After dialysis, freeze-dry or rotary evaporate the solution to obtain purified polysaccharides. Advantages
Preserve the integrity of the polysaccharide structure, suitable for small-scale laboratory use.
2. Organic solvent precipitation method Applicable scenarios
The DES contains components that are soluble in organic solvents (such as lactate-glucose DES). Step
1. Precipitation of polysaccharides: Add 4 times the volume of ethanol/acetone (final concentration 70%-80%) to the extract, and let it stand at 4℃ for 12 hours.
2. Centrifugation: Centrifuge at 4000 rpm for 10 minutes, and collect the precipitate (polysaccharides).
3. Washing: Wash the precipitate 2-3 times with 80% ethanol to remove residual DES.
4. Drying: Vacuum freeze-drying. Advantages
Fast, low cost, suitable for industrialization.
3. Macroporous resin adsorption method Applicable scenarios
The DES components have significant differences in polarity compared to the polysaccharides (for example, acidic DES). Step
1. Sample loading: Pass the extract through a large-pore resin column (such as AB-8, D101).
2. Elution: First, elute the DES components with 30% ethanol. Then, elute the polysaccharides with 70% ethanol.
3. Recovery: Collect the polysaccharide eluate, remove the ethanol by rotary evaporation, and freeze-dry it. Advantages
High selectivity, with a polysaccharide recovery rate of over 90%.
4. Ultrafiltration/Nanofiltration membrane separation Applicable scenarios
Large-scale production requires continuous operation. Step
1. Pre-treatment: Dilute the extract and adjust the pH to neutral.
2. Ultrafiltration: Use an ultrafiltration membrane with a molecular weight cut-off of 5-10 kDa. The permeate (DES component) can be recovered and reused.
3. Concentration: Further concentrate and dry the filtrate (containing polysaccharides). Advantages
Green and energy-efficient, DES can be recycled.
5. Reduce pressure distillation to recover DES Applicable scenarios
The DES has good thermal stability (such as choline chloride - citric acid). Step
1. Distillation: Perform vacuum rotary evaporation at 60-80℃ to recover DES (with a recovery rate of >85%).
2. Residue treatment: A small amount of residual DES can be removed by ethanol washing. Advantages
The solvent can be reused, reducing costs.
