Caffeic acid can be found in the bark of Eucalyptus globulus and the herbDipsacus asperoides. It can also be found in the freshwater fern Salvinia molesta and in the mushroom Phellinus linteus.
is an enzyme responsible for the transformation of caffeic acid into ferulic acid. Caffeic acid and related o-diphenols are rapidly oxidized by o-diphenol oxidases in tissue extracts.
Biodegradation
is an enzyme that uses caffeic acid and oxygen to produce 3--cis,cis-muconate.
Glycosides
and its isomers, are enzymic browning substrates found in dates.
Pharmacology
Caffeic acid has a variety of potential pharmacological effects in in vitro studies and in animal models, and the inhibitory effect of caffeic acid on cancer cell proliferation by an oxidative mechanism in the human HT-1080fibrosarcomacell line has recently been established. Caffeic acid is an antioxidantin vitro and also in vivo. Caffeic acid also shows immunomodulatory and anti-inflammatory activity. Caffeic acid outperformed the other antioxidants, reducing aflatoxin production by more than 95 percent. The studies are the first to show that oxidative stress that would otherwise trigger or enhance Aspergillus flavus aflatoxin production can be stymied by caffeic acid. This opens the door to use as a natural fungicide by supplementing trees with antioxidants. Studies of the carcinogenicity of caffeic acid have mixed results. Some studies have shown that it inhibits carcinogenesis, and other experiments show carcinogenic effects. Oral administration of high doses of caffeic acid in rats has caused stomach papillomas. In the same study, high doses of combined antioxidants, including caffeic acid, showed a significant decrease in growth of colon tumors in those same rats. No significant effect was noted otherwise. Caffeic acid is listed under some Hazard Data sheets as a potential carcinogen, as has been listed by the International Agency for Research on Cancer as a Group 2B carcinogen. More recent data show that bacteria in the rats' guts may alter the formation of metabolites of caffeic acid. Other than caffeic acid being a thiamine antagonist, there have been no known ill effects of caffeic acid in humans. Also, caffeic acid treatment attenuated lipopolysaccharide -induced sickness behaviour in experimental animals by decreasing both peripheral and central cytokine levels along with oxidative stress inflicted by LPS.
Chemistry
Caffeic acid is susceptible to autoxidation. Glutathione and thiol compounds or ascorbic acid have a protective effect on browning and disappearance of caffeic acid. This browning is due to the conversion of o-diphenols into reactive o-quinones. Chemical oxidation of caffeic acid in acidic conditions using sodium periodate leads to the formation of dimers with a furan structure. Caffeic acid can also be polymerized using the horseradish peroxidase/H2O2 oxidizing system.