The four most widely distributed hydroxycinnamic acids in fruits are p-coumaric, caffeic, ferulic
and sinapic acids (Figure 3) (Macheix et al. 1990). Hydroxycinnamic acids usually occur in various
conjugated forms, the free forms being artefacts from chemical or enzymatic hydrolysis during tissue
extraction. The conjugated forms are esters of hydroxyacids such as quinic, shikimic and tartaric
acid, as well as their sugar derivatives (Schuster and Herrmann 1985, Macheix et al. 1990, Shahidi
and Naczk 1995).