ABSTRACT
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.
