Produce Degradation Pathways and Prevention

202 Produce Degradation: Reaction Pathways and their Prevention

most important in terms of the color of produce, other polyphenols may contribute
to yellow and brown colors directly or their molecules may condense with antho-
cyanins and cause so-called “co-pigmentation.” Numerous publications cover
research related to many kinds of polyphenols, making it very difficult and some-
times impossible to divide the reviews into separate parts related to individual groups
such as anthocyanins or other flavonoids.

7.4.2 CHEMICAL PROPERTIES AND OCCURRENCE OF ANTHOCYANINS

Many authors consider anthocyanins as a special subgroup of flavonoids with a basic
structure of a falvylium cation (see Figure 7.5) that contains a pyran ring with a
positive charge. Anthocyanins may be defined as “glycosylated polyhydroxy and
polymethoxy derivatives of 2-phenylbenzopyrylium (flavylium) salts” (Brouillard,
1982). An addition of hydroxy and methoxy functional groups in specified positions
of the flavylium cation leads to compounds known as anthocyanidins. Approximately
20 anthocyanidins are known, but only six are considered important in produce.
These are pelargonidin, cyanidin, delfinidin, peonidin, petunidin, and malvinidin
(Francis, 1985a). These anthocyanidins occurring in produce are shown in Figure
7.6 (a)-(f). Since anthocyanidins do not contain sugar residues they may be consid-
ered aglycones of anthocyanins. Formation of esters with one or more sugars leads
to formation of anthocyanins. Sugars occuring most commonly in anthocyanins are
glucose, rhamnose, galactose, xylose, and arabinose. These sugars may further react
to form esters. P-coumaric, caffeic, ferulic, sinapic, p-hydroxybenzoic, malonic, and
acetic acids participate most frequently in this reaction (Brouillard, 1982).
Anthocyanins are water-soluble components of cell sap that give red and blue
colors to many fruits and vegetables. The color of anthocyanins is considered the
most important quality attribute in many processed food products. Numerous factors,
including the structure of the anthocyanins involved, concentration, solvent, pH, the
presence of other substances, and temperature, influence the nature and stability of
this color. The number and location of the hydroxy and methoxy groups in the
anthocyanin molecule affect its color properties.
In water solutions the molecules of anthocyanins exist in several forms in a
dynamic equilibrium that may be changed by a change in the parameters of the
system. In a slightly acidic pH range at room temperature the following four species

FIGURE 7.5Flavylium cation.

O

2

3

5 4

6

7

8 1

2' 4'

5'

1'

3'

A C

B