pigments in nectarines and peaches. Some varieties may also contain cyanidine
3-acetylglucoside and cyanidin 3-galactoside. Quercetin 3-glucoside and quercetin
3-rutinoside are the major flavonols in nectarines and peaches and are found mainly
in the skin [24].
Different phenolic compounds have been found in peach fruits. They are one of
the richest in antioxidant substances. However, both the qualitative and quantitative
profiles of these compounds vary considerably depending on the variety. In addition
to phenolic compounds in peach fruit, a number of vitamins are also present, with
significant amounts of ascorbic acid (vitamin C) and carotenoids (provitamin A).
Different conditions before and after ripening of fruit can change the synthesis and
emission of volatile substances from harvested plant products. This affects taste,
ripening, and other factors that affect quality or storage potential. The peach content
of volatile substances has been thoroughly studied. Up to now, more than one
hundred volatile compounds have been identified. Some of the most common are
linalool, benzaldehyde, ester terpenoids, norisoprenoids, ketones, and lactones.
Color properties are predominantly determined by lactones and fewer aldehydes,
alcohols, terpenoids. The chemical composition of the volatile compounds varies
between the different parts of the fruit. In the mesocarp, closer to the skin, for
example, the concentration of volatile substances such as norisoprenoids and
benzaldehydes is higher than in the inner mesocarp close to the stone. Besides the
composition during the ripening process, the chemical composition of the volatile
substances is changing: the levels of the six carbon compounds are drastically
reduced, while the content of lactones, benzaldehyde, linalool, norisoprenoids, and
phenylalanine derivatives is increased. Volatile ingredients are also influenced by the
conditions of fruit storage [25] (Fig. 2).
According to their biosynthetic origin, the secondary metabolites in plants can be
divided into three main groups: terpenoids, nitrogen-containing compounds (alkaloids, glucosinolates, and cyanohydrins), and phenylpropanoids, also known as
phenolic compounds [26]. One of the most important building blocks associated
with the biosynthesis of secondary metabolites is obtained from acetyl coenzyme A,
shikimic acid, mevalonic acid, and 1-deoxyxylose-5-phosphate. They participate,
respectively, in the acetate, shikimate, mevalonate, and deoxyxylose phosphate
pathways of biosynthesis [7, 26, 27].
4
Biosynthetic Pathways of Major Secondary Metabolites:
Enzymes and Regulation
All plants have the capacity to produce secondary metabolites (SMs). The widest
variety of them is found in the flower plants. The majority of these metabolites
originate from five different precursors or metabolic pathways. These are acetyl
coenzyme A (polyketides such as anthraquinones, flavonoids), active isoprene
(various terpenoids), shikimic acid (aromatic amino acids, cinnamic acids, tannins,
indole, and isoquinoline alkaloids), glycolysis (sugars, gallic acid), and TCA
16 Deranged Physiology of Peach
383
3-acetylglucoside and cyanidin 3-galactoside. Quercetin 3-glucoside and quercetin
3-rutinoside are the major flavonols in nectarines and peaches and are found mainly
in the skin [24].
Different phenolic compounds have been found in peach fruits. They are one of
the richest in antioxidant substances. However, both the qualitative and quantitative
profiles of these compounds vary considerably depending on the variety. In addition
to phenolic compounds in peach fruit, a number of vitamins are also present, with
significant amounts of ascorbic acid (vitamin C) and carotenoids (provitamin A).
Different conditions before and after ripening of fruit can change the synthesis and
emission of volatile substances from harvested plant products. This affects taste,
ripening, and other factors that affect quality or storage potential. The peach content
of volatile substances has been thoroughly studied. Up to now, more than one
hundred volatile compounds have been identified. Some of the most common are
linalool, benzaldehyde, ester terpenoids, norisoprenoids, ketones, and lactones.
Color properties are predominantly determined by lactones and fewer aldehydes,
alcohols, terpenoids. The chemical composition of the volatile compounds varies
between the different parts of the fruit. In the mesocarp, closer to the skin, for
example, the concentration of volatile substances such as norisoprenoids and
benzaldehydes is higher than in the inner mesocarp close to the stone. Besides the
composition during the ripening process, the chemical composition of the volatile
substances is changing: the levels of the six carbon compounds are drastically
reduced, while the content of lactones, benzaldehyde, linalool, norisoprenoids, and
phenylalanine derivatives is increased. Volatile ingredients are also influenced by the
conditions of fruit storage [25] (Fig. 2).
According to their biosynthetic origin, the secondary metabolites in plants can be
divided into three main groups: terpenoids, nitrogen-containing compounds (alkaloids, glucosinolates, and cyanohydrins), and phenylpropanoids, also known as
phenolic compounds [26]. One of the most important building blocks associated
with the biosynthesis of secondary metabolites is obtained from acetyl coenzyme A,
shikimic acid, mevalonic acid, and 1-deoxyxylose-5-phosphate. They participate,
respectively, in the acetate, shikimate, mevalonate, and deoxyxylose phosphate
pathways of biosynthesis [7, 26, 27].
4
Biosynthetic Pathways of Major Secondary Metabolites:
Enzymes and Regulation
All plants have the capacity to produce secondary metabolites (SMs). The widest
variety of them is found in the flower plants. The majority of these metabolites
originate from five different precursors or metabolic pathways. These are acetyl
coenzyme A (polyketides such as anthraquinones, flavonoids), active isoprene
(various terpenoids), shikimic acid (aromatic amino acids, cinnamic acids, tannins,
indole, and isoquinoline alkaloids), glycolysis (sugars, gallic acid), and TCA
16 Deranged Physiology of Peach
383