Fumaric acid, also known as donic acid, is an organic compound with a dicarboxylic acid structure corresponding to (E) -butenediic acid, or transbutenedioic acid; the isomer found in nature, instead of the cis isomer. It intervenes in the cellular metabolism, having participation in the Krebs cycle. It is used in the processing and preservation of foods because of its powerful antimicrobial action. As a food additive, it is used as an acidity regulator, it is a food acidulant used since 1946.
It is non-toxic, and is generally used in beverages and baking powders for which high purity requirements are required. It is generally used as a substitute for citric acid, in a ratio of 1.36 g of citric acid for each 0.91 grams of fumaric acid, to add acidity.