Kojic acid


Kojic acid is a chelation agent produced by several species of fungi, especially Aspergillus oryzae, which has the Japanese common name koji. Kojic acid is a by-product in the fermentation process of malting rice, for use in the manufacturing of sake, the Japanese rice wine. It is a mild inhibitor of the formation of pigment in plant and animal tissues, and is used in food and cosmetics to preserve or change colors of substances. It forms a bright red complex with ferric ions.

Biosynthesis

13C-Labeling studies have revealed at least two pathways to kojic acid. In the usual route, dehydratase enzymes convert glucose to kojic acid. Pentoses are also viable precursors in which case dihydroxyacetone is invoked as an intermediate.

Applications

Kojic acid may be used on cut fruits to prevent oxidative browning, in seafood to preserve pink and red colors, and in cosmetics to lighten skin. As an example of the latter, it is used to treat skin diseases like melasma. Kojic acid also has antibacterial and antifungal properties.
The cocrystals of kojic acid with quercetin were found to have two times better cytotoxic activity to human cervical cancer cells and human colon cancer cells in comparison with quercetin itself.

Other effects

Kojic acid has been shown to protect Chinese hamster ovary cells against ionizing radiation-induced damage. Dogs pretreated with kojic acid after whole-body exposure to a lethal dose of 3 Gy gamma radiation had a 51-day survival rate of 66.7% versus the dogs in the 3 Gy irradiation only group, which all died within 16 days of postirradiation.