vegetables [49]. Moreover, UVC light is also very popular in the field of enhancing
the production of resveratrol in grape berries and its derivatives, including grape
juice and wine. In fact, UVC treatment is the most efficient elicitor at increasing the
stilbene content in grapes, in particular trans-resveratrol.
The use of UVC light as an elicitor in grapevines was first described by Langcake
and Pryce (1977) [50]. The authors observed an increase in trans-resveratrol
concentration in leaves after irradiation (in vitro). Thereafter, many studies were
developed in vineyards to determine the mechanisms and possible applications of
this tool [51, 52]. However, the majority of the above studies were performed on
leaves due to their availability during the vegetative cycle of grapevines.
In 2000, UVC light was applied for the first time in the postharvest treatment of
table grapes [53]. Later, the treatment was optimized to maximize the resveratrol
concentration in grapes [54]. The optimized treatment (1040w. 40 cm and 1 min) has
been widely applied to different Vitis subspecies, varieties, areas of production,
conditions, years, etc.
Regarding postharvest UVC treatment, two parameters should be taken into
account. First, the maximum resveratrol concentration achieved, and second, the
time required to reach this maximum concentration after the postharvest UVC
treatment (called Dm). Obviously, the activation of plant defense mechanisms
requires few days. Dm is a key factor to sure the quality of the grapes. If Dm is
too long, grapes will lose quality, making them unsuitable for producing wine.
Therefore, varieties achieving a high resveratrol concentration in a short time period
guarantee quality stilbene-enriched grapes [24].
The induction capacity of grapes from three varieties of Vitis vinifera sylvestris
(VS9, VS15, and VS16), seven of Vitis vinifera sativa (Merlot, Syrah, Graciano,
Tempranillo, Palomino fi Graciano, Tempran, and Tintilla de Rota), and two hybrid
direct-producer vines (Regent and Orion) after postharvest UVC treatment has been
described for two harvests. Four compounds were identified in UVC treated grapes:
piceatannol, trans-resveratrol, ε-viniferin, and δ-viniferin [24]. Varieties belonging
to the sylvestris group and the Merlot variety presented high stilbene production.
Syrah, Vitis vinifera sylvestris V15, Pinot noir, and Graciano stood out for their
capacity to induce piceatannol, while Vitis sylvestris V9 and Syrah stood out for
presenting the highest ε-viniferin concentrations after UVC treatment. Therefore, it
could be established that the effectiveness of the UVC treatment depends on both
variety and year, but not on the subspecies. As mentioned above, effectiveness is
determined not just for the maximum concentration but also for Dm. Moreover, the
authors concluded that from a technological point of view it is vitally important to
consider the variability between years, since the number of days to reach the
maximum concentration might also vary.
Terroir (climate and soil) is also considered a key factor for the effectiveness
of postharvest UVC treatments [33]. Indeed, terroir factor was stronger than variety
factor regarding stilbene induction capacity upon UVC treatment. In that study,
the induction capacity of stilbenes was studied on four red grape varieties cultivated
in four Andalusian terroirs. In agreement with previous data, the Syrah variety
obtained the highest stilbene concentration, especially in Cabra (Córdoba) terroir
26 Preharvest Methyl Jasmonate and Postharvest UVC Treatments: Increasing. . .
631
the production of resveratrol in grape berries and its derivatives, including grape
juice and wine. In fact, UVC treatment is the most efficient elicitor at increasing the
stilbene content in grapes, in particular trans-resveratrol.
The use of UVC light as an elicitor in grapevines was first described by Langcake
and Pryce (1977) [50]. The authors observed an increase in trans-resveratrol
concentration in leaves after irradiation (in vitro). Thereafter, many studies were
developed in vineyards to determine the mechanisms and possible applications of
this tool [51, 52]. However, the majority of the above studies were performed on
leaves due to their availability during the vegetative cycle of grapevines.
In 2000, UVC light was applied for the first time in the postharvest treatment of
table grapes [53]. Later, the treatment was optimized to maximize the resveratrol
concentration in grapes [54]. The optimized treatment (1040w. 40 cm and 1 min) has
been widely applied to different Vitis subspecies, varieties, areas of production,
conditions, years, etc.
Regarding postharvest UVC treatment, two parameters should be taken into
account. First, the maximum resveratrol concentration achieved, and second, the
time required to reach this maximum concentration after the postharvest UVC
treatment (called Dm). Obviously, the activation of plant defense mechanisms
requires few days. Dm is a key factor to sure the quality of the grapes. If Dm is
too long, grapes will lose quality, making them unsuitable for producing wine.
Therefore, varieties achieving a high resveratrol concentration in a short time period
guarantee quality stilbene-enriched grapes [24].
The induction capacity of grapes from three varieties of Vitis vinifera sylvestris
(VS9, VS15, and VS16), seven of Vitis vinifera sativa (Merlot, Syrah, Graciano,
Tempranillo, Palomino fi Graciano, Tempran, and Tintilla de Rota), and two hybrid
direct-producer vines (Regent and Orion) after postharvest UVC treatment has been
described for two harvests. Four compounds were identified in UVC treated grapes:
piceatannol, trans-resveratrol, ε-viniferin, and δ-viniferin [24]. Varieties belonging
to the sylvestris group and the Merlot variety presented high stilbene production.
Syrah, Vitis vinifera sylvestris V15, Pinot noir, and Graciano stood out for their
capacity to induce piceatannol, while Vitis sylvestris V9 and Syrah stood out for
presenting the highest ε-viniferin concentrations after UVC treatment. Therefore, it
could be established that the effectiveness of the UVC treatment depends on both
variety and year, but not on the subspecies. As mentioned above, effectiveness is
determined not just for the maximum concentration but also for Dm. Moreover, the
authors concluded that from a technological point of view it is vitally important to
consider the variability between years, since the number of days to reach the
maximum concentration might also vary.
Terroir (climate and soil) is also considered a key factor for the effectiveness
of postharvest UVC treatments [33]. Indeed, terroir factor was stronger than variety
factor regarding stilbene induction capacity upon UVC treatment. In that study,
the induction capacity of stilbenes was studied on four red grape varieties cultivated
in four Andalusian terroirs. In agreement with previous data, the Syrah variety
obtained the highest stilbene concentration, especially in Cabra (Córdoba) terroir
26 Preharvest Methyl Jasmonate and Postharvest UVC Treatments: Increasing. . .
631