(up to 33 mg kg
À1 f.w.) with limestone soil, a high average temperature and low
average relatively humidity.
Therefore, the use of postharvest UVC light to increase grape stilbene content is
quite difficult to standardize due to the numerous factors involved. However, certain
conclusions can be reached: (i) each variety seems to be influenced to a different
degree by the climate and harvest; (ii) varieties with high induction capacity and
consequently a short Dm are highly recommended; (iii) Syrah is the particular
variety proposed for projects aimed at producing wine enriched in stilbenes.
More recently, UV-C light application as a preharvest treatment tool to induce
stilbenoid production was tested in open field experiments for table grapes [55]. UVC light application preharvest day, output power, exposure time, and storage conditions were optimized.
UV-C light preharvest treatment was applied at different days before
grape ripeness to establish the optimum application day to reach the maximum
trans-resveratrol concentration. Grapes were illuminated with an UV-C light dose
of 1866 J m
À2 (1040 W, 1 min) on 7, 5, 3, and 1 days prior to the optimal harvest day.
Maximum trans-resveratrol concentration was achieved after 24 h regardless
of application day. An increase between 22- and 46-fold as compared with the
control concentration was achieved. trans-Resveratrol concentration reached a
maximal concentration in grape (19 mg kg
À1 f.w. skin), 24 h after illumination
(10.000 J m
À2 ), and subsequently declined. Preharvest UV-C light treatment might
reduce the required time in 2 days to reach maximum trans-resveratrol concentration
in comparison with postharvest UV-C light treatment. In 2002, a Dm value for Red
Globe equal to five when postharvest UV-C light was established [56].
trans-Resveratrol was affected not only by the dose but also by how the dose
was applied in terms of output power and exposure time. When postharvest storage
was studied, trans-resveratrol increased for 3 days, after which time a reduction was
observed. The mechanism for hormesis proposed by Luckey [57] suggested that low
doses of UV-C could inflict repairable damage to DNA and this slight trauma would
activate repair mechanisms for radiation-induced DNA damage. This suggests that
sublethal radiation may stimulate vital processes inside the cells and create a positive
change in the homoeostasis of the plant physiology. A dose over approximately
10,000 J m
À2 approximately seemed to reduce trans-resveratrol concentration
compare with lower dose [55]. Similar trends were found for ε-viniferin, whose
concentration at days 3 and 4 reached similar levels to those of trans-resveratrol.
UV-C light increased its concentration between 5- and 31-fold depending
on the treatment and sampling day. Maximum concentrations of 28,42 and 26,75
mg kg
À1 f.w. skin were found on postharvest day 4 in grapes treated with 520 W for
10 min and 1040 W for 5 min, respectively.
Moreover, daily periodic preharvest UV-C light treatment showed a cumulative
effect on grape stilbenoids, reaching a trans-resveratrol concentration around (120 mg
kg
À1 f.w. skin) [58]. The results for grape trans-resveratrol after daily periodic
preharvest UV-C light treatment compared with the results after a single treatment
demonstrated that a higher concentration was reached with each periodic treatment
under comparable conditions. Periodic preharvest UV-C light treatment maintained a
632
S. Cruz et al.
À1 f.w.) with limestone soil, a high average temperature and low
average relatively humidity.
Therefore, the use of postharvest UVC light to increase grape stilbene content is
quite difficult to standardize due to the numerous factors involved. However, certain
conclusions can be reached: (i) each variety seems to be influenced to a different
degree by the climate and harvest; (ii) varieties with high induction capacity and
consequently a short Dm are highly recommended; (iii) Syrah is the particular
variety proposed for projects aimed at producing wine enriched in stilbenes.
More recently, UV-C light application as a preharvest treatment tool to induce
stilbenoid production was tested in open field experiments for table grapes [55]. UVC light application preharvest day, output power, exposure time, and storage conditions were optimized.
UV-C light preharvest treatment was applied at different days before
grape ripeness to establish the optimum application day to reach the maximum
trans-resveratrol concentration. Grapes were illuminated with an UV-C light dose
of 1866 J m
À2 (1040 W, 1 min) on 7, 5, 3, and 1 days prior to the optimal harvest day.
Maximum trans-resveratrol concentration was achieved after 24 h regardless
of application day. An increase between 22- and 46-fold as compared with the
control concentration was achieved. trans-Resveratrol concentration reached a
maximal concentration in grape (19 mg kg
À1 f.w. skin), 24 h after illumination
(10.000 J m
À2 ), and subsequently declined. Preharvest UV-C light treatment might
reduce the required time in 2 days to reach maximum trans-resveratrol concentration
in comparison with postharvest UV-C light treatment. In 2002, a Dm value for Red
Globe equal to five when postharvest UV-C light was established [56].
trans-Resveratrol was affected not only by the dose but also by how the dose
was applied in terms of output power and exposure time. When postharvest storage
was studied, trans-resveratrol increased for 3 days, after which time a reduction was
observed. The mechanism for hormesis proposed by Luckey [57] suggested that low
doses of UV-C could inflict repairable damage to DNA and this slight trauma would
activate repair mechanisms for radiation-induced DNA damage. This suggests that
sublethal radiation may stimulate vital processes inside the cells and create a positive
change in the homoeostasis of the plant physiology. A dose over approximately
10,000 J m
À2 approximately seemed to reduce trans-resveratrol concentration
compare with lower dose [55]. Similar trends were found for ε-viniferin, whose
concentration at days 3 and 4 reached similar levels to those of trans-resveratrol.
UV-C light increased its concentration between 5- and 31-fold depending
on the treatment and sampling day. Maximum concentrations of 28,42 and 26,75
mg kg
À1 f.w. skin were found on postharvest day 4 in grapes treated with 520 W for
10 min and 1040 W for 5 min, respectively.
Moreover, daily periodic preharvest UV-C light treatment showed a cumulative
effect on grape stilbenoids, reaching a trans-resveratrol concentration around (120 mg
kg
À1 f.w. skin) [58]. The results for grape trans-resveratrol after daily periodic
preharvest UV-C light treatment compared with the results after a single treatment
demonstrated that a higher concentration was reached with each periodic treatment
under comparable conditions. Periodic preharvest UV-C light treatment maintained a
632
S. Cruz et al.