Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

262 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
Table 12.1
The major classes of phenolic compounds present in fruits
Number of Carbon
carbons skeleton Class and subclass Example
6 C 6 Simple phenols Catechol
7 C 6 C 1 Hydroxybenzoates (phenolic
acids)
Gallic acid, protocatechuic acid, syringic
acid, gentisic acid, p-hydroxybenzoic acid
9 C 6 C 3 Hydroxycinnamates
Caffeic, p-coumaric, ferulic, isoferulic
(phenolic acids)
Coumarins
Scopoletin, aesculetin, umbelliferone,
limmettin, herniarin
10 C 6 C 4 Naphthoquinones Juglone
13 C 6 C 1 C 6 Xanthones Mangiferin, mangostin, gartanins
14 C 6 C 2 C 6 Stilbenes Resveratrol
15 C 6 C 3 C 6 Flavonoids
Flavanone
Naringenin, hesperetin, neohesperidin,
eriodictyol, citromitin, pinostrobin
Flavone
Luteolin, apigenin, tangeretin, nobiletin,
sinensetin
Flavonol
Quercetin, kaempferol, myricetin
Flavan-3-ol
Catechin, epicatechin, gallocatechins,
epigallocatechin, epicatechin gallate
Anthocyanins
Cyanidin, delphinidin, malvidin, peonidin,
petunidin, pelargonidin
Dihydrochalcones
Phloretin, phloridzin
18 (C 6 C 3 )2 Lignans Secoisolariciresinol, matairesinol
30 (C 6 C 3 C 6 )2 Biflavonoids Amentoflavone
n (C 6 C 3 )n Lignins Guaiacyl lignins
n (C 6 C 1 )n: Hydrolysable tannins
Gallotannins, ellagitannins, castalagin,
Glu
corilagin, chebulagic acid
n (C 6 C 3 C 6 )n Condensed tannins
(flavolans)
Procyanidins (catechin polymers)
Adapted from Harborne (1980).
12.3 Distribution of phenolic acids in fruits
In literature, both hydroxybezoates and hydroxycinnamates and their derivatives are referred
collectively as phenolic acids. Phenolic acids are found predominantly and widely
in almost all fruits (Herrmann, 1989) (Table 12.2). The most commonly found hydroxycinnamic
acids are p-coumaric, caffeic, ferulic, and sinapic acids, while p-hydroxybenzoic,
protocatechuic, vanillic, and syringic acids are the common hydroxybenzoic acids in fruits.
These derivatives differ in their structure only by the degree of the hydroxylations and
methoxylations of their aromatic rings. In fruits, phenolic acids are commonly found as
conjugated forms with quinic acid. It seems that chlorogenic acid, which is derived from
caffeic and quinic acids, is the most common hydroxybenzoic acid derivative in berry,
pome, and stone fruits (Mattila et al., 2006). The general term “chlorogenic acid” includes
three positional isoforms. These isoforms differ from one another based on which hydroxyl
group of quinic acid is used to combine the two precursor molecules, quinic acid and
caffeic acid. The following common (and chemical) names have been given to these isoforms:
chlorogenic acid (5-caffeoylquinic acid), cryptochlorogenic acid (4-caffeoylquinic
acid), and neochlorogenic acid (3-caffeoylquinic acid). The presence of chlorogenic acid