Food
It is generally used in beverages and baking powders for which requirements are placed on purity. It is generally used as a substitute for tartaric acid and occasionally in place of citric acid, at a rate of 1.36 g of citric acid to every 0.91 grams of Fumaric Acid to add sourness, similar to the way Malic Acid is used. It is also used as a coagulant in stove top pudding mixes.

Biology
Fumarate is an intermediate in the citric acid cycle used by cells to produce energy in the form of adenosine triphosphate (ATP) from food. It is formed by the oxidation of succinate by the enzyme succinate dehydrogenase. Fumarate is then converted by the enzyme fumarase to malate. Human skin naturally produces Fumaric acid when exposed to sunlight

Chemistry
Chemistry Fumaric aAntly, industrial synthesis of Fumaric acid is mostly based on catalytic isomerisation of maleic acid in aqueous solutions at low pH. Maleic acid is accessible in large volumes as a hydrolysis product of maleic anhydride, produced by catalytic oxidation of benzene or butane.

The chemical properties of Fumaric Acid can be anticipated from its component functional groups. This weak acid forms a diester, it undergoes additions across the double bond, and it is an excellent dienophile.

Other uses

Fumaric Acid is used in the manufacture of polyester resins and polyhydric alcohols and as a mordant for dyes.