Indigo pigments are one of the oldest pigments known to mankind and are widely used in food, medicine and printing and dyeing industries. The use of indigo as a fabric dye can be traced back to at least 2500 BC. Some of the clothes worn by ancient Egyptian mummies and the blue linen fabrics unearthed from Mawangdui in my country are all dyed with indigo. A branch of the Yao ethnic group in my country is named "Blue Indigo Yao" because of its unique technology of producing and using indigo dyeing cloth.
In the food industry, indigo is used as a
Food Coloring in its sodium sulfonate salt or its aluminum form. In China, it is called "brilliant blue" and brilliant blue aluminum precipitation. In the United States, it is mainly in the form of sodium sulfonate salt and is called "indigo pigment".
Physical and Chemical Properties
Solubility: slightly soluble in water, ethanol, glycerin and propylene glycol, insoluble in oils and fats. 0.05% aqueous solution is dark blue. 1g can be dissolved in about 100ml of water at 25℃. The solubility in water is lower than that of other edible synthetic pigments. 0.05% aqueous solution is blue. Soluble in glycerin, propylene glycol, slightly soluble in ethanol, insoluble in oils and fats. It is dark blue when exposed to concentrated sulfuric acid, blue after dilution, and its aqueous solution is green to yellow-green when sodium hydroxide is added.
Indigo is easy to color, has a unique hue, and is widely used. It has poor heat resistance, light resistance, alkali resistance, oxidation resistance, salt resistance, and bacterial resistance. It fades when reduced. If it is reduced with sodium hyposulfite or glucose, it becomes indigo white. The maximum absorption wavelength is 610nm±2nm.
The Uses of Indigo Blue
It is mainly used for dyeing cotton yarn, cotton cloth, wool or silk. This pigment is a pigment-treated product of the important reducing dye indigo. It has excellent light resistance, weather fastness and heat stability, gives a blue tone, and can be prepared into a liquid dispersion dosage form. It is mainly used for viscose fiber pulp coloring and printing and dyeing. It is used for biochemical agents and indicators, as well as dyeing of cotton yarn, cotton cloth, wool or silk.
As a food colorant, my country stipulates that it can be used in red and green silk, with a maximum usage of 0.02g/kg; in fruit juice (flavored) drinks, carbonated drinks, mixed wines, candies, pastries, dyed canned cherries (for decoration), and green plums, the maximum usage is 0.10g/kg; the maximum usage in pickled side dishes is 0.01g/kg.
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