due to the accumulation of carbohydrates and other nutrients that support the growth
of insect larvae. The phenolic composition of the bumps consists of up to 70% of
gallic acid esters [19].
Gallic acid is the major unit of gallotannins whereas gallic acid and hexahydroxydiphenoyl residues are both subunits of ellagitannins. Gallotannins and
ellagitannins are called hydrolyzable tannins because they are easily degraded,
releasing gallic acid and/or ellagic acid, while condensed tannins are not. Condensed
tannins and hydrolysis tannins are capable of binding and precipitating collagen
proteins in animal skins [13].
The main precursor to phenylpropanoids is cinnamic acid and its derivatives –
hydroxycinnamates. The most common hydroxycinnamates are p-coumaric, caffeic,
and ferulic acids, which are often accumulated as corresponding tartrate esters,
caftaric, and fetaric acids. Conjugates of caffeic acid are common components of
fruits and vegetables [13].
Members of the stilbene family having a C6–C2–C6 structure, such as flavonoids,
are polyphenol compounds. Phytoalexins are compounds produced from plants in
response to an attack by fungal, bacterial, and viral pathogens. Resveratrol is the
most common stilbene [20].
Alkaloids are a large and structurally diverse group of compounds. Many are
derived from amino acids, but others are the result of modifying different classes of
molecules, including polyphenols, terpenes, or steroids. With some notable exceptions, alkaloids are the most soluble aqueous alcoholic solutions and commonly
occur as salts (e.g., chlorides or sulfates) or as N-oxides in plants. Most of these have
heterocyclic ring nitrogen or a ring system and a basic (alkaline) nature.
3
Distribution of Secondary Metabolites in Peach Tissues
The tissue distribution of secondary metabolites in peaches varies greatly and
depends on varieties and environmental conditions. The main pigment responsible
for the red coloration of peaches and nectarines is cyanidin – in particular, cyanidine
3-glucoside, one of the most common anthocyanin pigments in fruit. The
hydroxycarboxylic acid derivatives, anthocyanins, flavonols, and flavan 3-ols are
the most common phenols in peaches and nectarines. Peaches and nectarines contain
cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, flavonols (quercetin-3-O-glucoside and quercetin-3-O-rutinoside), flavan 3-ols (catechin, epicatechin, and proanthocyanidins, including procyanidin B1), and others [5, 21, 22]. Apricots and
peaches contain carotenoids mainly in the form of β-carotene [23]. Chlorogenic
acids, caffeic acid, catechin, and procyanidin B3 (catechin- (4β-8) -catechin) are the
major phenols in peaches. Chlorogenic and non-chlorogenic acids are the main
derivatives of hydroxycinnamic acid, while procyanidin B1 (epicatechin- (4β-8)
-catechin), catechin, and epicatechin are the predominant flavan 3-ols and flavonols
found in peach skin compared to peach flesh. Anthocyanins are mainly found in
peach and nectarine skin. Small amounts of pigments can also be found in the tissues
near the stone. Cyanidine 3-glucoside and cyanidin 3-rutinoside are the main
382
L. Koleva-Valkova and A. Harizanova
of insect larvae. The phenolic composition of the bumps consists of up to 70% of
gallic acid esters [19].
Gallic acid is the major unit of gallotannins whereas gallic acid and hexahydroxydiphenoyl residues are both subunits of ellagitannins. Gallotannins and
ellagitannins are called hydrolyzable tannins because they are easily degraded,
releasing gallic acid and/or ellagic acid, while condensed tannins are not. Condensed
tannins and hydrolysis tannins are capable of binding and precipitating collagen
proteins in animal skins [13].
The main precursor to phenylpropanoids is cinnamic acid and its derivatives –
hydroxycinnamates. The most common hydroxycinnamates are p-coumaric, caffeic,
and ferulic acids, which are often accumulated as corresponding tartrate esters,
caftaric, and fetaric acids. Conjugates of caffeic acid are common components of
fruits and vegetables [13].
Members of the stilbene family having a C6–C2–C6 structure, such as flavonoids,
are polyphenol compounds. Phytoalexins are compounds produced from plants in
response to an attack by fungal, bacterial, and viral pathogens. Resveratrol is the
most common stilbene [20].
Alkaloids are a large and structurally diverse group of compounds. Many are
derived from amino acids, but others are the result of modifying different classes of
molecules, including polyphenols, terpenes, or steroids. With some notable exceptions, alkaloids are the most soluble aqueous alcoholic solutions and commonly
occur as salts (e.g., chlorides or sulfates) or as N-oxides in plants. Most of these have
heterocyclic ring nitrogen or a ring system and a basic (alkaline) nature.
3
Distribution of Secondary Metabolites in Peach Tissues
The tissue distribution of secondary metabolites in peaches varies greatly and
depends on varieties and environmental conditions. The main pigment responsible
for the red coloration of peaches and nectarines is cyanidin – in particular, cyanidine
3-glucoside, one of the most common anthocyanin pigments in fruit. The
hydroxycarboxylic acid derivatives, anthocyanins, flavonols, and flavan 3-ols are
the most common phenols in peaches and nectarines. Peaches and nectarines contain
cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, flavonols (quercetin-3-O-glucoside and quercetin-3-O-rutinoside), flavan 3-ols (catechin, epicatechin, and proanthocyanidins, including procyanidin B1), and others [5, 21, 22]. Apricots and
peaches contain carotenoids mainly in the form of β-carotene [23]. Chlorogenic
acids, caffeic acid, catechin, and procyanidin B3 (catechin- (4β-8) -catechin) are the
major phenols in peaches. Chlorogenic and non-chlorogenic acids are the main
derivatives of hydroxycinnamic acid, while procyanidin B1 (epicatechin- (4β-8)
-catechin), catechin, and epicatechin are the predominant flavan 3-ols and flavonols
found in peach skin compared to peach flesh. Anthocyanins are mainly found in
peach and nectarine skin. Small amounts of pigments can also be found in the tissues
near the stone. Cyanidine 3-glucoside and cyanidin 3-rutinoside are the main
382
L. Koleva-Valkova and A. Harizanova