In food

p-Coumaric acid can be found in a wide variety of edible plants and fungi such as peanuts, navy beans, tomatoes, carrots, basil and garlic.^{[citation needed]} It is found in wine and vinegar.^[3] It is also found in barley grain.^[4]

p-Coumaric acid from pollen is a constituent of honey.^[5]

Derivatives

p-Coumaric acid glucoside can also be found in commercial breads containing flaxseed.^[6] Diesters of p-coumaric acid can be found in carnauba wax.

Biosynthesis

It is biosynthesized from cinnamic acid by the action of the P450-dependent enzyme 4-cinnamic acid hydroxylase (C4H).

 ${\displaystyle {\begin{matrix}{}\\{\xrightarrow {\mathrm {C4H} }}\\{}\end{matrix}}}$ 

It is also produced from L-tyrosine by the action of tyrosine ammonia lyase (TAL).

 ${\displaystyle {\xrightarrow {\mathrm {TAL} }}}$  + NH₃ + H⁺

Biosynthetic building block

p-Coumaric acid is the precursor of 4-ethylphenol produced by the yeast Brettanomyces in wine. The enzyme cinnamate decarboxylase catalyzes the conversion of p-coumaric acid into 4-vinylphenol.^[7] Vinyl phenol reductase then catalyzes the reduction of 4-vinylphenol to 4-ethylphenol. Coumaric acid is sometimes added to microbiological media, enabling the positive identification of Brettanomyces by smell.

cis-p-Coumarate glucosyltransferase is an enzyme that uses uridine diphosphate glucose and cis-p-coumarate to produce 4′-O-β-D-glucosyl-cis-p-coumarate and uridine diphosphate (UDP). This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases.^[8]

Phloretic acid, found in the rumen of sheep fed with dried grass, is produced by hydrogenation of the 2-propenoic side chain of p-coumaric acid.^[9]

The enzyme, resveratrol synthase, also known as stilbene synthase, catalyzes the synthesis of resveratrol ultimately from a tetraketide derived from 4-coumaroyl CoA.^[10]

p-Coumaric acid is a cofactor of photoactive yellow proteins (PYP), a homologous group of proteins found in many eubacteria.^[11]