Maltose is pretty rare or absent in nectars, and although it tastes sweet to
honeybees, it is usually less attractive for them than sucrose [49, 88]. Earlier it
was believed that maltose is synthesized in nectar itself [89], but its presence in
nectar is due to the fact that maltose is a degradation product of starch (obtained from
chloroplasts during starch degradation in night), while nectar secretion in flower
starts with starch degradation [90]. Also, maltose is a major product of catabolism of
starch in guard cells which can be found within the flower [91]. In regard to
disaccharide isomaltose, it is more related to honeydew then to nectar, so that is
the reason why honeydew honeys had significantly higher mean values of this sugar
than the blossom honeys. In unifloral cherry honey, the concentration of the isomaltose was around 0.80% [92].
4.2
Phenolic Compounds in Cherry Nectars
Phenolic compounds are widespread natural constituents and their main function is
to protect plants against various biotic and abiotic stresses. Their multiple roles in
floral nectars and the relationship with pollinators were outlined in the literature [28].
Mainly, phenolics are associated with functions such as attracting pollinators or
repelling nectar thieves, maintaining nectar in a microbe-free state, being important
components of floral scents. Their role in cherry pollination could be the same,
although yet not proved. Some phenolic compounds together with some other
constituents may accumulate in floral nectar due to passive absorption by the nectar
[30].
Although numerous flavonoids have been described in literature, their presence in
floral nectar was not studied extensively. The same applies for the composition of
cherry nectar topic. Often phenolic composition was reported only qualitatively [93],
where floral nectar chemical compositions of 29 species native to Argentinian
Patagonia and phenolic composition measured on qualitative scale were reported.
A scarce number of papers show that nectar phenolic profile is characterized both by
various phenolic aglycones and their derivatives. In rosemary nectar, kaemferol-3sophoroside and quercetin-3-sophoroside were identified as the most abundant
among 15 different flavonoids [94], while in Portuguese heather nectar (Erica sp.)
flavonol aglycones quercetin, kaempferol, myricetin, and isorhamnetin were identified [95]. The occurrence of flavonols in higher plants was associated with lignification in cell walls and with UV absorption of flowers, as nectar guide [96]. Also,
functional roles of flavonols as developmental regulators and/or signaling molecules
in plants were discussed [97].
Although nectar composition of various sour cherry cultivars was examined [46],
studies on floral nectar in terms of detailed phenolic characterization were not
performed until the investigation of phenolic diversity in floral nectar of different
“Oblačinska” sour cherry clones [64]. The phenolic complexity of sour cherry nectar
was apparent and the qualitative phenolic profile was shown to be characterized
mostly with flavonol glycosides. All identified glycosides were derivatives of
kaempferol, quercetin, and isorhamnetin [64] (Table 1).
764
M. F. Akšić et al.
honeybees, it is usually less attractive for them than sucrose [49, 88]. Earlier it
was believed that maltose is synthesized in nectar itself [89], but its presence in
nectar is due to the fact that maltose is a degradation product of starch (obtained from
chloroplasts during starch degradation in night), while nectar secretion in flower
starts with starch degradation [90]. Also, maltose is a major product of catabolism of
starch in guard cells which can be found within the flower [91]. In regard to
disaccharide isomaltose, it is more related to honeydew then to nectar, so that is
the reason why honeydew honeys had significantly higher mean values of this sugar
than the blossom honeys. In unifloral cherry honey, the concentration of the isomaltose was around 0.80% [92].
4.2
Phenolic Compounds in Cherry Nectars
Phenolic compounds are widespread natural constituents and their main function is
to protect plants against various biotic and abiotic stresses. Their multiple roles in
floral nectars and the relationship with pollinators were outlined in the literature [28].
Mainly, phenolics are associated with functions such as attracting pollinators or
repelling nectar thieves, maintaining nectar in a microbe-free state, being important
components of floral scents. Their role in cherry pollination could be the same,
although yet not proved. Some phenolic compounds together with some other
constituents may accumulate in floral nectar due to passive absorption by the nectar
[30].
Although numerous flavonoids have been described in literature, their presence in
floral nectar was not studied extensively. The same applies for the composition of
cherry nectar topic. Often phenolic composition was reported only qualitatively [93],
where floral nectar chemical compositions of 29 species native to Argentinian
Patagonia and phenolic composition measured on qualitative scale were reported.
A scarce number of papers show that nectar phenolic profile is characterized both by
various phenolic aglycones and their derivatives. In rosemary nectar, kaemferol-3sophoroside and quercetin-3-sophoroside were identified as the most abundant
among 15 different flavonoids [94], while in Portuguese heather nectar (Erica sp.)
flavonol aglycones quercetin, kaempferol, myricetin, and isorhamnetin were identified [95]. The occurrence of flavonols in higher plants was associated with lignification in cell walls and with UV absorption of flowers, as nectar guide [96]. Also,
functional roles of flavonols as developmental regulators and/or signaling molecules
in plants were discussed [97].
Although nectar composition of various sour cherry cultivars was examined [46],
studies on floral nectar in terms of detailed phenolic characterization were not
performed until the investigation of phenolic diversity in floral nectar of different
“Oblačinska” sour cherry clones [64]. The phenolic complexity of sour cherry nectar
was apparent and the qualitative phenolic profile was shown to be characterized
mostly with flavonol glycosides. All identified glycosides were derivatives of
kaempferol, quercetin, and isorhamnetin [64] (Table 1).
764
M. F. Akšić et al.