hydroxycinnamic

Hydroxycinnamic acids are a group of phenolic compounds based on the cinnamic acid skeleton that feature hydroxy substitutions on the aromatic ring. The core structure consists of a phenyl ring attached to a trans-ethylene side chain (C6-C3). The best-known members include p-coumaric acid (4-hydroxycinnamic acid), caffeic acid (3,4-dihydroxycinnamic acid), and ferulic acid (4-hydroxy-3-methoxycinnamic acid). These compounds may occur singly or as esters and derivatives in plants.

Natural occurrence and biosynthesis begin with the phenylpropanoid pathway. Phenylalanine is converted to cinnamic acid by phenylalanine ammonia-lyase, after which cinnamate 4-hydroxylase and related enzymes introduce hydroxyl or methoxy groups to yield the various hydroxycinnamates. They are widespread in fruits, vegetables, grains, coffee, tea, and other plant-derived foods, often present as free acids or bound in esters such as chlorogenic acid (caffeoylquinic acid).

Functions in plants include roles in structural lignin formation, suberin and lignan biosynthesis, and defense against pathogens and UV stress. In addition to their ecological roles, hydroxycinnamic acids contribute to flavor, aroma, and color in foods and beverages and are valued for their antioxidant properties. They serve as precursors for a range of secondary metabolites and polymers formed through enzymatic oxidation and radical coupling.

In industrial and nutritional contexts, hydroxycinnamic acids are studied for their potential health benefits and use as antioxidant additives. They can be extracted from plant matrices and are sometimes modified to form esters and polymers for research and application in food science, cosmetics, and materials chemistry.