Agriculture Reference
In-Depth Information
Hydroxycinnamic acids
Hydroxycinnamic acids occur in fruits mainly in bound
form in the form of esters of hydroxyl acids such as tartaric
and quinic acids or their sugar derivatives. Hydroxycin-
namic acids may also be linked with amines such as pu-
trescine, tyramine, and piperidine or with flavonoids, lignin,
suberin, and cutin (Macheix et al., 1990).
Hydroxycinnamic acids are found in all parts of the fruits,
but they are more concentrated in the outer part. The lev-
els of hydroxycinammic acid tend to decrease as the fruits
ripen (Manach et al., 2004). The predominant hyroxycin-
namic acid in many fruits is caffeic acid, but in citrus fruits
and pineapples, p-coumaric acid was found to be domi-
nant (Macheix et al., 1990). Chlorogenic acid is present
in tropical fruits such as avocado (Ramirez-Martinez and
Luh, 1973).
3'
2'
4'
1
8
O
2
5'
7
1'
6'
6
3
4
5
O
Figure 4.1.
Chemical structure of the basic
flavonoid skeleton.
tropical and subtropical fruits include anthocyanins, fla-
vanols, flavanones, flavanonols, flavones, and flavonols.
Anthocyanins
Anthocyanins are water-soluble colored or pigmented com-
pounds responsible for much of the red, blue, and purple
colors in fruits, vegetables, and ornamental crops. Almost
200 different anthocyanins have been identified in plants.
Of these, approximately 70 have been reported in fruits.
The composition and content of anthocyanins allow differ-
entiation of fruits from one another (Mazza and Miniati,
1994), for example, pink and green guavas.
Many tropical and subtropical fruits are characterized
by bright red or purple pigments, suggesting the presence
of anthocyanins, though reports of specific anthocyanin
contents of tropical fruits are somewhat limited (Edy et al.,
2007).
Hydroxybenzoic acids
Hydroxybenzoic acids are components of complex struc-
tures like hydrolysable tannins and lignin. Hydroxybenzoic
acids in tropical and subtropical fruits are generally low in
amount. Among this group, 4-hydroxybenzoic acid, a phe-
nolic derivative of benzoic acid, is used as a preservative
due to its low toxicity (Ritzer and Sundermann, 2000).
Polyphenols
Polyphenols are a diverse category of chemical compounds
found in plants that contain more than one benzene ring and
varying number of hydroxyl, carbonyl, and carboxylic acid
groups, which commonly exist with one or more attached
sugar moities. The most common class of polyphenols is
the flavonoids. Tropical and subtropical fruits are known to
be good sources of polyphenols, and their content can vary
tremendously between different fruits and within fruits of
the same type. Apart from the genetic differences, agro-
nomic practices, geographic location, and stress factors
(stress, diseases, minerals) influence the amount of phe-
nolic content in the fruits, too (Scalzo et al., 2005).
Occurrence
Anthocyanins are widely distributed in fruits and vegeta-
bles. Pomegranate is regarded to be rich in anthocyanins
with its juice having total anthocyanin content ranging from
161.9 to 387.4 mg/liter. The predominant anthocyanin in
pomegranate juice was cyaniding 3-glucoside (Gil et al.,
2000). Anthocyanin content of frozen litchi fruit was found
to be 5.21
Flavonoids
Flavonoids are polyphenolic compounds with a basic skele-
ton of diphenylpropanes (C
6
10
2
unit/g
in frozen litchi fruit sample treated with 1% HCL (Jiang
et al., 2004).
A study by Edy et al. (2007) found the anthocyanin con-
tent (mg/100 g, fresh weight basis) of some lesser known
tropical fruits such as jussara (
Euterpe edulis
), Guajiru
(
Chrysobalanus icaco
), and jambolao (
Syzygium cumini
)
to be 290, 104, and 79, respectively, while two acerola
(
Malphigia emarginata
) varieties had 23-48 mg/100 g
anthocyanins.
10
2
unit/g control samples and 7.8
×
×
C
6
) (Fig. 4.1)
with a different oxidation level of the central pyran ring.
Flavonoids are usually present as glycosides with a sugar
moiety linked through an OH group or through carbon-
carbon (C
+
C
3
+
C) bonds. Depending on structural features,
flavonoids can be further subdivided into anthocyanins,
catechins, chalcones, flavonones, flavonols, isoflavones,
flavanes, and flavanols. The common flavonoids found in
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