antihistaminic agents [66]. The finding that red wine presents more health-promoting
activity than beer or spirits has led to research focusing its attention on phenolic
compounds; within this group, stilbenes (in particular, trans-resveratrol) seem to
show high bioactivity. Therefore, a great deal of effort has been devoted to increasing the stilbene content of wines.
Strategies for increasing stilbenes levels in grapes have been already described in the
current chapter. Regarding factors which affect the stilbene concentration in wine,
oenological practices such as skin contact maceration, yeast strain, fining agent, filtration, and ageing seem to be important (Fig. 1). In general, all the processes that
maximize the extraction of phenols from skin are recommended [67]. Moreover, the
use of yeasts which have the gene of overexpressed STS have been suggested [68].
However, this method is not allowed in Europe. On the other hand, the use of fining
agents such as bentonite, casein, albumin, or PVPP reduced the resveratrol content in
wines enormously [67, 69]. In fact, although PVPP is one of the most-widely used
fining agents, it lacks selectivity and therefore it has a limited applicability. A new
polymer (P-NIOA) has shown a similar removal to PVPP, but with a lower affinity to
resveratrol [70]. Likewise, a filtration step may reduce resveratrol content by up to 58%
[71], while ageing hardly affected resveratrol content in red wines aged in oak barrels
[72]. To sum up, all processes involved in the final stage of wine production, but ageing,
reduce importantly the content of stilbenes in wine (Fig. 5).
A study performed on stilbene-enriched grapes concluded that the concentration
of trans-resveratrol decreased progressively during winemaking, especially during
AF, probably due to the interaction with yeast and/or other organic compounds in the
fermentation media [73].
In another more recent study, stilbene-enriched grapes obtained through a combination of MEJA+UVC treatments were used to make red wine following traditional methods to obtain a stilbene-enriched wine [39]. The results showed
that wines whose grapes were treated first with methyl jasmonate (before harvest)
and secondly with UVC light (after harvest) presented a twofold higher stilbene
concentration than the control. However, the concentration in bottled wine was
not very high (up to 2.32 mg l
À1 of total stilbenes). The stilbenes were lost during
the winemaking process, not only during alcoholic fermentation, as reported by
previously [73], but also during the following steps. At pressing, at racking, and at
cold stabilization wastes are generated (pomaces, lees and tartrates respectively)
(Fig. 5). Above wastes are stilbene-enriched by products (up to 25 gr Kg
À1 fw
waste). They were even proposed as a valuable source for manufacturing nutraceutical products [39]. It is also remarkable that in the study by Guerrero et al. [73], the
treated wines, with higher stilbene content, showed better chromatic properties and
obtained the highest scores at tasting.
4
Conclusions
Stilbene-enriched wines are claimed to be a rich source of bioactives. They provide
consumers with added value since their intake of stilbenes is significantly increased
while the consumption of ethanol remains the same.
26 Preharvest Methyl Jasmonate and Postharvest UVC Treatments: Increasing. . .
635
activity than beer or spirits has led to research focusing its attention on phenolic
compounds; within this group, stilbenes (in particular, trans-resveratrol) seem to
show high bioactivity. Therefore, a great deal of effort has been devoted to increasing the stilbene content of wines.
Strategies for increasing stilbenes levels in grapes have been already described in the
current chapter. Regarding factors which affect the stilbene concentration in wine,
oenological practices such as skin contact maceration, yeast strain, fining agent, filtration, and ageing seem to be important (Fig. 1). In general, all the processes that
maximize the extraction of phenols from skin are recommended [67]. Moreover, the
use of yeasts which have the gene of overexpressed STS have been suggested [68].
However, this method is not allowed in Europe. On the other hand, the use of fining
agents such as bentonite, casein, albumin, or PVPP reduced the resveratrol content in
wines enormously [67, 69]. In fact, although PVPP is one of the most-widely used
fining agents, it lacks selectivity and therefore it has a limited applicability. A new
polymer (P-NIOA) has shown a similar removal to PVPP, but with a lower affinity to
resveratrol [70]. Likewise, a filtration step may reduce resveratrol content by up to 58%
[71], while ageing hardly affected resveratrol content in red wines aged in oak barrels
[72]. To sum up, all processes involved in the final stage of wine production, but ageing,
reduce importantly the content of stilbenes in wine (Fig. 5).
A study performed on stilbene-enriched grapes concluded that the concentration
of trans-resveratrol decreased progressively during winemaking, especially during
AF, probably due to the interaction with yeast and/or other organic compounds in the
fermentation media [73].
In another more recent study, stilbene-enriched grapes obtained through a combination of MEJA+UVC treatments were used to make red wine following traditional methods to obtain a stilbene-enriched wine [39]. The results showed
that wines whose grapes were treated first with methyl jasmonate (before harvest)
and secondly with UVC light (after harvest) presented a twofold higher stilbene
concentration than the control. However, the concentration in bottled wine was
not very high (up to 2.32 mg l
À1 of total stilbenes). The stilbenes were lost during
the winemaking process, not only during alcoholic fermentation, as reported by
previously [73], but also during the following steps. At pressing, at racking, and at
cold stabilization wastes are generated (pomaces, lees and tartrates respectively)
(Fig. 5). Above wastes are stilbene-enriched by products (up to 25 gr Kg
À1 fw
waste). They were even proposed as a valuable source for manufacturing nutraceutical products [39]. It is also remarkable that in the study by Guerrero et al. [73], the
treated wines, with higher stilbene content, showed better chromatic properties and
obtained the highest scores at tasting.
4
Conclusions
Stilbene-enriched wines are claimed to be a rich source of bioactives. They provide
consumers with added value since their intake of stilbenes is significantly increased
while the consumption of ethanol remains the same.
26 Preharvest Methyl Jasmonate and Postharvest UVC Treatments: Increasing. . .
635