At present, there are many methods and processes applied to decolorization of traditional Chinese medicine, but they can be classified by the following methods.

 

   1、 The pigment was removed according to the solubility difference in different solvents

 

This is the most commonly used, the most simple, but also relatively poor results.

 

1. Water extraction and alcohol precipitation: a small part of water-soluble pigment can be removed.

 

Alcohol extraction and water precipitation: it can remove most of the fat soluble pigments.

 

(the two methods can also be used alternately)

 

2. Acid base precipitation method: for example, when the impurity pigment is some phenolic acid components such as flavonoids and anthraquinone, it can be adjusted below PH3, and the other precipitates.

 

2、 The pigment was removed according to the different distribution ratio in the two-phase solvent

 

For example, when the impurity pigment is some phenolic acid components such as flavonoids and anthraquinone, the method of adjusting pH to above 12 and extracting with organic solvent can be adopted. At this time, because the pigment exists in the form of dissociation, it is not suitable to be extracted.

 

3、 The separation was carried out according to the difference of adsorption between pigment and active component

 

1. Physical adsorption: (adsorption force is intermolecular force)

 

(1) Polar adsorbent: such as silica gel, alumina. It can remove hydrophilic pigment.

 

(2) Non polar adsorbent: such as activated carbon, pulp, talc powder, diatomite. It can remove lipophilic pigment.

 

Activated carbon is an excellent adsorbent, it has a strong adsorption capacity to pigment, bacteria, pyrogen and other impurities, and it also has a filtering effect.

 

There are a lot of micropores and voids in it, and the surface area can reach 200-500m2 / g.

 

Adsorption principle: because most of the pigments have conjugate double bond structure, they are easy to adsorb.

 

Usage: cold adsorption, thermal adsorption, carbon layer filtration, column chromatography adsorption.

 

2. Chemisorption

 

(1) For example, alkaline alumina can be used to remove some phenolic acid pigments such as flavonoids and anthraquinone.

 

(2) Ion exchange resin method: such as flavonoids, anthraquinone and other phenolic acid pigments can be removed by anion exchange resin.

 

3. Semi chemisorption: polyamide and macroporous resin. The adsorption mechanism is hydrogen bonding, and the macroporous resin also has part of van der Waals force.

 

Polyamide can form hydrogen bonds with phenolic hydroxyl groups of phenols and flavonoids through amide carbonyl groups in molecules. Hydrogen bonds can also be formed by free amino groups on amide bonds and carbonyl groups on quinones and fatty acids.

    4、 Depigmentation by precipitation

 

Representative substance: milk of lime.

 

Common concentration: 20% - 30%.

 

Decolorization principle: calcium ions in lime milk can combine with the effective components and impurities in the liquid medicine to form calcium chelate and calcium salt precipitation. The calcium salts formed by flavonoids, anthraquinones, phenols, saponins, some alkaloids and calcium ions can be decomposed under the action of sulfuric acid, and then dissolved in water. However, tannins, some proteins, organic acids, polar pigments and polysaccharides can not be decomposed.

 

5、 Removal of pigment by flocculant

 

1. The commonly used flocculants are as follows:

 

(1) Gelatin: tannins affect the stability of the solution and are easy to change color. Gelatin and tannin administrative complex can be used to precipitate together with suspended particles in water

 

(2) ZTC1 + 1 natural clarifying agent:

 

It can be divided into four types: type I: deproteinized

 

Type II: decolorization and clarification

 

Type III: Traditional Chinese medicine oral liquid and granule type, can replace alcohol precipitation method, play a role in removing unstable components and assisting filtration.

 

IV type: injection type, mainly to improve the clarity.

 

(3) 101 juice clarifier:

 

(4) Chitin and chitosan: chitosan is obtained by acetylation of chitin. They are all natural cationic flocculants.

 

2. Factors affecting the clarification effect

 

(1) Dosage of clarifier

 

(2) Preparation concentration and adding sequence of clarifier

 

(3) The concentration of the solution itself

 

(4) Effect of temperature on flocculation

 

(5) The influence of pH value of the solution

 

(6) The influence of stirring speed and stirring time

 

(7) Effect of flocculation and sedimentation time

 

6、 Removal of pigment by membrane separation

 

The most commonly used technology is ultrafiltration