Phenolic acids are found abundantly in foods and divided into
two classes: derivatives of benzoic acid and derivatives of cinnamic
acid. The hydroxybenzoic acid content of edible plants is
generally low, with the exception of certain red fruits, black radish
and onions, which can have concentrations of several tens
of milligrams per kilogram fresh weight.7
The hydroxycinnamic
acids are more common than hydroxybenzoic acids and consist
chiefly of p-coumaric, caffeic, ferulic and sinapic acids.