chapter  19
Phenolic Compounds in Foods
Pages 60

Hyoung S. Lee Florida Department of Citrus Research and Education Center,

Lake Alfred, Florida, U.S.A.

I. OCCURRENCE IN FOODS

Phenolic compounds are a diverse class of chemicals

containing a hydroxyl group on a benzene ring.

Some phenolics are complex molecules derived from

the condensation of two or more components from

either shikimic acid or polyketide pathways. Phenolic

compounds can be further divided into separate com-

ponents classes, listed in Table 1. Pheonolic acids occur

naturally in a wide range of bound forms. They usually

occur in the form of esters rather than glycosides. They

may be conjugated with organic acids, sugars, amino

compounds, lipids, terpenoids, or other phenolics. The term phenolic acids encompass the seven

carbon benzoic acids (C1-C6) and nine carbon

cinnamic acids (C3-C6). Protocatechuic acid, p-hydro-

xybenzoic acid, vanillic acid, gallic acid, and syringic

acid are the principal benzoic acids. Salicylic acid and

gentisic acid which possess a hydroxyl group ortho to

the carboxylic acid function are also often found in

foods. Gallic acid occurs as quinic acid esters and is

often found in plants as its dimer, ellagic acid. Caffeic,

p-coumaric, ferulic, and sinapic acids are the most

common cinnamic acids. Cinnamic acids, since they

possess a double bond, are capable of existing in two

isomeric forms, cis-and trans-cinnamic acid. The

naturally occurring cinnamic acids have the more

stable trans configuration. However, cis-and trans-

isomers can undergo transformation into the other

form under certain conditions.