In the modern food industry, pigment is a widely used food additive. Curcumin is a natural pigment extracted and refined from plants, curcumin is safe, reliable, non-toxic and has no side effects. It is one of the seven natural pigments widely used in countries all over the world.
Curcumin Coloring Mechanism
The molecular formula of curcumin is C21H20O6. The chemical structure includes two ortho-methylated phenols and a β-diketone functional group,
Insoluble in acidic and neutral solutions, soluble in alkaline solutions. Since the hydrogen atoms on the β-diketone chain of curcumin can undergo intramolecular transfer, its molecular structure exists in the form of keto-enol tautomers.
The ketone form exists mainly in acidic and neutral aqueous solutions. The enol form is mainly present in alkaline aqueous solution. The enol form is stabilized by resonance-assisted hydrogen bonding.
The solubility and stability of curcumin are related to the type of solvent and pH. Curcumin solutions exhibit different colors at different pH. It is yellow under acidic and neutral conditions, and red under alkaline conditions. At pH 7.2, the curcumin solution was still yellow but started to precipitate. When the pH was 9.9, the solution was red with precipitation.
Curcumin has good stability to reducing agents. It has strong coloring power and is not easy to fade after being colored. It is not only an excellent natural colorant in the food industry, but also widely used in the chemical industry (such as cosmetics, hair dyes, pharmaceutical industry (such as tablet coats) and other fields.
Curcumin Coloring Use
Curcumin is bright in color, has good coloring and dispersibility, and its dyeing ability is more remarkable than other natural pigments and synthetic limonin, especially for proteins. It is mainly used for the coloring of sausage products, canned food, sauce and stewed products, etc.
Curcumin has poor water solubility and is slightly soluble in oil. Using physical and chemical processes, it can be made into alcohol-soluble, water-soluble and oil-soluble, etc., and various product specifications can be applied to different food coloring needs. In addition, the water-soluble and oil-soluble curcumin is compounded with other natural pigments, so the product changes from a single pure yellow to orange, brown and other natural pigment products.
Prospect
In recent years, nanotechnology not only solves the problem of curcumin is insoluble in water but also improves the stability of curcumin and prolongs the retention time of coloring. The chemical modification of curcumin and its compounding with other pigments will become the development trend in the field of food coloring in the future.