What are the common decolorization methods used in food processing?

According to the color in different solvents solubility difference decolorization
1. water alcohol precipitation: can remove a small portion of water-soluble pigments. Alcohol precipitation: can remove most of the fat-soluble pigments. (Can also be used alternately)
2. Acid-base precipitation method: for example, when the impurity pigment is some flavonoids, anthraquinones and other phenolic acidic components, can be adjusted below PH3, so that it precipitates.
According to the pigment in the two-phase solvent distribution ratio of different decolorization
For example, when the impurity pigment is a number of flavonoids, anthraquinones and other phenolic acidic components, can be taken to adjust the PH to 12 or more, the method of extraction with organic solvents. At this time, because the pigment are in the form of dissociation, should not be extracted.
Decolorization according to the difference in adsorption of pigments and active ingredients

1, physical adsorption: (adsorption force is intermolecular force) (1) polar adsorbent: such as silica gel, alumina. Can remove hydrophilic pigment. (2) Non-polar adsorbent: such as activated carbon, pulp, talc, diatomaceous earth. It can remove lipophilic pigment.
Activated carbon is an excellent adsorbent, it has a strong adsorption capacity for pigment, bacteria, pyrogen and other impurities, and it also has the role of filtering. It has a large number of micropores and voids, and its surface area can reach 200-500m2/g. Adsorption principle: Since most pigments have the structure of co-choked double bond, it is easy to be adsorbed.
Usage: cold adsorption method, heat adsorption method, carbon layer filtration method, column chromatography adsorption method.
2、Chemical adsorption (1) For example, alkaline alumina can be used to remove some flavonoids, anthraquinones and other phenolic acid pigments. (2) Ion exchange resin method: for example, flavonoids, anthraquinones and other phenolic acid pigments can be removed by anion exchange resin.
(3) Semi-chemical adsorption: Polyamide and macroporous resin. The principle of adsorption is hydrogen bonding, and the macroporous resin also has part of the van der Waals force.
Polyamide can be through the molecular amide carbonyl and phenolic hydroxyl phenols, flavonoids form hydrogen bonds. Hydrogen bonds can also be formed between the free amine group on the amide bond and the carbonyl group on quinones and aliphatic carboxylic acids.
Removal of pigments by precipitation
Representative substance: milk of lime. Common concentration: 20%-30%.
Principle of decolorization: Calcium ions in milk of lime can combine with some ingredients to form calcium chelate and calcium salt precipitation. And precipitation in the role of sulfuric acid, flavonoids, anthraquinones, phenols, saponins, some alkaloids and calcium ions formed by calcium salts can be broken down, and then dissolved into water. But tannins, some proteins, organic acids, polar pigments, polysaccharides, etc. cannot be broken down.
Flocculant method to remove coloring
1, the food industry commonly used flocculants and application scope Polyacrylamide, commonly used in beverage process, sugar process, fermentation process; disodium phosphate, trisodium phosphate, commonly used in beverage process, fermentation process; sulfuric acid, commonly used in beer process, fermentation process, starch process, dairy processing process; zinc sulfate is commonly used in the process of leather eggs, beer process, fermentation process; ferrous sulfate, commonly used in beverages and beer process Ferrous sulfate is commonly used in beverage and beer process;
2、Factors affecting the flocculation effect (1) the effect of temperature; (2) the effect of pH value of water; (3) the nature and structure of flocculants; (4) the effect of flocculant dosage; (5) the effect of stirring speed and time;
Membrane separation for pigment removal is most commonly used as ultrafiltration technology.