*3.1.1 Colour development*

The colour of red and white Port wines is one of the main quality parameters of the different Port wines styles. For Port wines made from red grape varieties, the initial wine colour is mainly due to the anthocyanins extracted from grape skins during vinification. Nevertheless, in a young Port wine, the percentage of colour due to the so called polymeric pigments is already 23 to 30% indicating that changes in the compounds responsible for the colour have already started during the short alcoholic fermentation and wine spirit addition to stop the alcoholic fermentation. The red Port wine colour increases up to 80% during the first months of ageing depending on the concentration of free acetaldehyde present in the young wine. After 46 weeks of ageing, the polymeric pigments can make up 78 and 98% of the wine colour [12]. The colour evolution during ageing is explained by the involvement of anthocyanins in different equilibria in solution and their simultaneous transformation through various concurring chemical reactions to a range of other pigments, many of them still unknown (**Figure 3**).

#### **Figure 3.**

*Colour evolution during ageing by the involvement of anthocyanins in different equilibria and their simultaneous transformation through various concurring chemical reactions to a range of other pigments (references are listed in Table 2).*

**127**

substituents) (**Figure 3**).

*Port Wine: Production and Ageing*

*DOI: http://dx.doi.org/10.5772/intechopen.94900*

changes occurring during White Port wine ageing.

anthocyanin-4-bisulphite adducts [16] (IX).

These changes are dependent on the wine composition like anthocyanin, flavonol and tannin concentrations, different processing parameters like temperature, oxygen level, pH and the presence of other compounds either produced during alcoholic fermentation, added during processing or formed during the ageing process. On the other hand, no studies have been reported about the colour

Anthocyanins in aqueous solution, depending on the pH, occur in different forms present in equilibria [13–15]. At pH < 2, the red flavylium cation is the main structure present (I in **Figure 3**). With increasing pH, for values between 3 and 6, after hydration of the flavylium cation, the colourless hemiketal (II) structure is formed, this last being in equilibrium with the pale yellow *cis*-chalcone (III) through tautomerisation. This chalcone isomer is also in equilibrium with the *trans*chalcone isomer (IV). With the pH increase, the flavylium cation is deprotonated to the corresponding violet neutral quinoidal bases (V and VI) that at higher pH yields the blue anionic quinoidal bases after further deprotonation (VII and VIII, **Figure 3**) [15]. When sulphur dioxide (SO2) is present, there is observed reversible bleaching of anthocyanins that occurs due to the formation of the colourless

Considering all these equilibriums, at wine pH (3–4) these pigments would be expected to be present mainly in their non-coloured hemiketal form (II). However, the flavylium cation (I) is the main form present in young red wines. This is the result of its stabilisation by different copigmentation mechanisms such as selfassociation and interaction with other wine components [17–20]. In the copigmentation process, anthocyanins and other colourless organic compounds, such as flavonoids, amino acids, organic acids, polysaccharides, anthocyanins, or metallic ions, form molecular or complex associations [21]. The copigmentation is based in two effects [22]: (1) the formation of the π–π complex which causes changes in the spectral properties of the molecules in the flavylium ion, increasing the absorption intensity (hyperchromic effect) and its wavelength (bathochromic shift); and (2) the stabilisation of the flavylium form by the π complex displaces the equilibrium in such way that the red colour increases. This association also gives protection for the water nucleophilic attack in the 2 position of the flavylium cation [23] and for other species such as peroxides and sulphur dioxide in the 4 position [24, 25], so that the balance is displaced from hydrated forms towards the red flavylium cations. If the copigment is other anthocyanin, a self-association is formed (X); in the case of copigments with free electron pairs, an intermolecular copigmentation takes place (XI) finally, in the most complex case, the copigmentation can be carried out by a part of the structure itself (usually one of the aromatic acyl group

During wine ageing, the concentration of monomeric anthocyanins starts to decrease leading to the formation of new anthocyanin derived pigments with different colour features and greater colour expression at high pH, important for the long-term colour stability of aged red wines [21]. The formation of most of the anthocyanin-derived pigments occurs in the first months of ageing, as the oxidative conditions in oak barrels favour their formation [26, 27]. Copigmentation has been hypothesised as the first mechanism involved in the formation of polymeric anthocyanin-derived pigments in red wines during ageing [19]. Numerous pigments have been characterised in wines and wine-like model solutions, and can be classified into three groups with respect to their formation pathways: 1) Direct condensation between anthocyanins and flavonols; 2) Condensation between anthocyanins and flavonols mediated by aldehydes, mainly acetaldehyde; and 3) Pyroanthocyanins (**Figure 3**). Although some of these pigments have only been detected in very small quantities in red wines,

### *Port Wine: Production and Ageing DOI: http://dx.doi.org/10.5772/intechopen.94900*

*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

cialisation depending on the desired White Port wine colour type.

*3.1.1 Colour development*

**3.1 Chemical changes and sensory development during Port wine ageing**

White Port wine is made in the same way as red Port wines. However, there is a tendency to reduce the skin contact time, and even to ferment clarified grape juice at a lower temperature (18–20°C), to obtain wines with fruity aromas. The wines are aged in small size old wood barrels for a minimum of three years before its commer-

The colour of red and white Port wines is one of the main quality parameters of the different Port wines styles. For Port wines made from red grape varieties, the initial wine colour is mainly due to the anthocyanins extracted from grape skins during vinification. Nevertheless, in a young Port wine, the percentage of colour due to the so called polymeric pigments is already 23 to 30% indicating that changes in the compounds responsible for the colour have already started during the short alcoholic fermentation and wine spirit addition to stop the alcoholic fermentation. The red Port wine colour increases up to 80% during the first months of ageing depending on the concentration of free acetaldehyde present in the young wine. After 46 weeks of ageing, the polymeric pigments can make up 78 and 98% of the wine colour [12]. The colour evolution during ageing is explained by the involvement of anthocyanins in different equilibria in solution and their simultaneous transformation through various concurring chemical reactions to a range of other pigments, many of them still unknown (**Figure 3**).

**126**

**Figure 3.**

*(references are listed in Table 2).*

*Colour evolution during ageing by the involvement of anthocyanins in different equilibria and their simultaneous transformation through various concurring chemical reactions to a range of other pigments*  These changes are dependent on the wine composition like anthocyanin, flavonol and tannin concentrations, different processing parameters like temperature, oxygen level, pH and the presence of other compounds either produced during alcoholic fermentation, added during processing or formed during the ageing process. On the other hand, no studies have been reported about the colour changes occurring during White Port wine ageing.

Anthocyanins in aqueous solution, depending on the pH, occur in different forms present in equilibria [13–15]. At pH < 2, the red flavylium cation is the main structure present (I in **Figure 3**). With increasing pH, for values between 3 and 6, after hydration of the flavylium cation, the colourless hemiketal (II) structure is formed, this last being in equilibrium with the pale yellow *cis*-chalcone (III) through tautomerisation. This chalcone isomer is also in equilibrium with the *trans*chalcone isomer (IV). With the pH increase, the flavylium cation is deprotonated to the corresponding violet neutral quinoidal bases (V and VI) that at higher pH yields the blue anionic quinoidal bases after further deprotonation (VII and VIII, **Figure 3**) [15]. When sulphur dioxide (SO2) is present, there is observed reversible bleaching of anthocyanins that occurs due to the formation of the colourless anthocyanin-4-bisulphite adducts [16] (IX).

Considering all these equilibriums, at wine pH (3–4) these pigments would be expected to be present mainly in their non-coloured hemiketal form (II). However, the flavylium cation (I) is the main form present in young red wines. This is the result of its stabilisation by different copigmentation mechanisms such as selfassociation and interaction with other wine components [17–20]. In the copigmentation process, anthocyanins and other colourless organic compounds, such as flavonoids, amino acids, organic acids, polysaccharides, anthocyanins, or metallic ions, form molecular or complex associations [21]. The copigmentation is based in two effects [22]: (1) the formation of the π–π complex which causes changes in the spectral properties of the molecules in the flavylium ion, increasing the absorption intensity (hyperchromic effect) and its wavelength (bathochromic shift); and (2) the stabilisation of the flavylium form by the π complex displaces the equilibrium in such way that the red colour increases. This association also gives protection for the water nucleophilic attack in the 2 position of the flavylium cation [23] and for other species such as peroxides and sulphur dioxide in the 4 position [24, 25], so that the balance is displaced from hydrated forms towards the red flavylium cations. If the copigment is other anthocyanin, a self-association is formed (X); in the case of copigments with free electron pairs, an intermolecular copigmentation takes place (XI) finally, in the most complex case, the copigmentation can be carried out by a part of the structure itself (usually one of the aromatic acyl group substituents) (**Figure 3**).

During wine ageing, the concentration of monomeric anthocyanins starts to decrease leading to the formation of new anthocyanin derived pigments with different colour features and greater colour expression at high pH, important for the long-term colour stability of aged red wines [21]. The formation of most of the anthocyanin-derived pigments occurs in the first months of ageing, as the oxidative conditions in oak barrels favour their formation [26, 27]. Copigmentation has been hypothesised as the first mechanism involved in the formation of polymeric anthocyanin-derived pigments in red wines during ageing [19]. Numerous pigments have been characterised in wines and wine-like model solutions, and can be classified into three groups with respect to their formation pathways: 1) Direct condensation between anthocyanins and flavonols; 2) Condensation between anthocyanins and flavonols mediated by aldehydes, mainly acetaldehyde; and 3) Pyroanthocyanins (**Figure 3**). Although some of these pigments have only been detected in very small quantities in red wines,

they have unique spectroscopic features that may, in some way, contribute together to the overall colour of aged red wines. In the first case, free anthocyanins can condense directly with flavan-3-ols and oligomeric proanthocyanins generating tannin-anthocyanins condensation products (T-A<sup>+</sup> , XII) or anthocyanin-tannin condensation products (A<sup>+</sup> -T, XIII) [8, 28–33]. The T-A<sup>+</sup> formation begins with the acid cleavage of the interflavanic bond of a procyanidin, giving a carbocation T+ which reacts with the hydrated form of the anthocyanin (II). This mechanism leads to a colourless compound (T-AOH) which easily dehydrates to the coloured flavylium form T-A<sup>+</sup> [34]. In the formation of A<sup>+</sup> -T pigments, nucleophilic addition of the flavanol takes place onto the flavylium form of the anthocyanin, yielding a colourless compound with the anthocyanin in flavene form. This flavene can be oxidised, resulting in a coloured flavylium A<sup>+</sup> -T pigment (XIII) or in a colourless compound A(-O-)T with a type-A bond (XIV) [31] (**Figure 3**). As described for the monomeric anthocyanins, these pigments can also occur in a dynamic equilibrium among some molecular forms, mainly the quinoidal base, the flavylium cation and the hemiketal or carbinol pseudobase [30]. Both T-A<sup>+</sup> pigments and colourless A(-O-)T have been detected in wines [35]. Dimeric anthocyanins (XVI) consisting of one unit under flavylium cation and the other one under hydrated hemiketal form (A<sup>+</sup> -AOH) were also characterised by mass spectrometry in wine like solutions [36] (**Figure 3**).

The A<sup>+</sup> -T adducts can generate yellow-orange xanthylium pigments (XV) by further structural rearrangements. After the dehydration, a new heterocyclic pyran ring is formed and the xanthylium structure is generated [17, 37–40] (**Figure 3**). However, xanthylium pigments are also proposed to be formed directly from oligomeric flavan-3-ols [41, 42].

On the other hand, the acetaldehyde-mediated polymerisation between either only flavanols or with anthocyanins is the most well documented reaction in the literature [31, 37, 43–51]. Acetaldehyde is the main aldehyde (90%) present in wines as a result of yeast metabolism during the first stages of alcoholic fermentation, being also produced throughout the wine ageing process from ethanol oxidation [52]. In fortified wines like Port wines, this compound and other aldehydes (propionaldehyde, 2-methylbutyraldehyde, isovaleraldehyde, methylglyoxal, benzaldehyde) are present in higher amounts due to the addition of wine spirit (40–260 mg/L of acetaldehyde) to stop the alcoholic fermentation [53]. Ethyl-linked products, including ethyl-linked flavanols [54, 55] and ethyl-linked anthocyanin-flavanol pigments (XVII) [55] have been detected in wines (**Figure 2**). The formation of ethyl-linked anthocyanin oligomers (A<sup>+</sup> -Et-AOH, XVIII) was also shown to occur both in model solution and in wine [56]. The ethyl-linked 8,8-malvidin-3-glucoside dimer was characterised by NMR under biflavylium cation forms [56]. However, physicochemical studies carried out on this pigment showed that the dimer under monoflavylium cation is the most abundant form at wine pH [57].

Another important group of anthocyanin derived pigments formed during ageing, also found in red Port wines, are the pyranoanthocyanins (XIX) (**Figure 3**). Pyranoanthocyanins are a group of anthocyanin-derived pigments [58, 59], which were first discovered in red wine by Cameira-dos-Santos et al. [60]. Pyranoanthocyanins are structurally characterised by the presence of a fourth ring between C-4 and the 5-hydroxyl group of an anthocyanin moiety, differing from each other on the type of group or molecule linked to the C-10 of the new ring [58, 61, 62]. The pyranic ring in pyranoanthocyanins provides protection against the nucleophilic attack from water or bisulphite, increasing their stability [63], making these compounds exceptionally stable pigments towards sulphite bleaching

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pyruvic acid by the yeast.

6 year aged wines, respectively).

the C-10 position of vitisin A [90].

(at pH 2) more colour than grape anthocyanins.

*DOI: http://dx.doi.org/10.5772/intechopen.94900*

and pH variations. Both anthocyanin-flavanol derived pigments, direct ones and ethyl-linked ones, show less stability during ageing than pyranoanthocyanins. Through the reaction of anthocyanins with acetaldehyde [61, 63], pyruvic acid [58, 64], cinnamic acids [65, 66], acetoacetic acid [64], and procyanidins in the presence of acetaldehyde [67], several different classes of these pigments have been identified in the past decade such as vitisins [58, 59, 61, 68, 69], hydroxyphenyl-pyranoanthocyanins (pinotins) [59, 64, 70–72], methylpyranoanthocyanins [59, 73], vinylflavanol-pyranoanthocyanins [59], portisins [58, 59, 61, 66, 67, 74, 75], and more recently a new family of pyranoanthocyanin dimers [28, 73, 76, 77] (**Table 2**). Pyruvic acid leads to the major pyranoanthocyanins determined in wines, i.e. carboxy-pyranoanthocyanins (R = COOH), sometimes referred to as vitisin A [58, 59, 61, 68, 69]. In red Port wines, it is the main pigment found during ageing. Due to its particular vinification process, the concentration of vitisin A is very high: 51.2 mg/L for Touriga Nacional Port wines, for example [78]. Indeed, wine fortification after alcoholic fermentation allows greater availability of pyruvic acid [79], which leads to reaching the highest contents shortly after fermentation and during the first year of ageing, followed by a slow decline [80]. After one year of ageing in barrels, the contents decrease by about 15–25% and about 70% after two years, whereas it is not so much important during bottle ageing (9–18%). Romero and Bakker [81] have demonstrated that the addition of pyruvic acid to finished Port wines from four different grape varieties resulted in an increase of malvidin-pyruvic acid adducts. It was also found that the concentration of anthocyanin-pyruvic acid adducts in wines was directly related to the original grape anthocyanin profile; the higher the initial anthocyanin precursor forms, the higher the concentration of corresponding adducts [81–83]. Morata et al. [84] have reported that the yeast strain used in the alcoholic fermentation (inoculated or not) also affects the production of malvidin-3-glucoside-pyruvate, existing a direct relation between the concentration of the pigment and the production of

Moreover, the content of SO2 in must can also influence the production of malvidin-3-glucoside-pyruvate, since SO2 regulates the concentration of pyruvic

Romero and Bakker [68] have reported that malvidin-derived pyruvic acids adduct in model solutions provided approximately 11-fold (at pH 3) and 14-fold

Flavanol pyranoanthocyanins are formed by the cycloaddition between anthocyanins and 8-vinylflavanol adducts initially derived from the cleavage of ethyl-linked flavanol oligomers [46] or pigments [86, 87]. In red Port wines, pyranoanthocyanin-procyanidin dimers were identified in higher concentrations than the corresponding pyranoanthocyanin-catechins, representing up to 80% of the total pyranomalvidin-flavanols. This postulate is concordant with the fact that procyanidin dimers are more abundant than catechin monomers in grapes and wines from the Douro region [88, 89]. Furthermore, their concentrations decreased in older wines for both malvidin-3-glucoside derived-pigments (10.59 mg/L in 3 year aged wines, 9.16 mg/L in 4 year aged wines and 7.86 mg/L in 6 year aged wines) and associated coumaroyl pigments (6.62, 5.51 and 3.33 mg/L in 3, 4 and

A second generation of pyranoanthocyanins can be formed by the reaction between a vitisin A and other metabolites. For example, oxovitisins (XX) are neutral yellowish pyranone structures involving the nucleophilic attack of water at

acid through the formation of a weak bisulphite addition compound [85].

## *Port Wine: Production and Ageing DOI: http://dx.doi.org/10.5772/intechopen.94900*

*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

tannin-anthocyanins condensation products (T-A<sup>+</sup>

one under hydrated hemiketal form (A<sup>+</sup>

from oligomeric flavan-3-ols [41, 42].

spectrometry in wine like solutions [36] (**Figure 3**).

The formation of ethyl-linked anthocyanin oligomers (A<sup>+</sup>

condensation products (A<sup>+</sup>

flavylium form T-A<sup>+</sup>

T+

T-A<sup>+</sup>

The A<sup>+</sup>

they have unique spectroscopic features that may, in some way, contribute together to the overall colour of aged red wines. In the first case, free anthocyanins can condense directly with flavan-3-ols and oligomeric proanthocyanins generating


the acid cleavage of the interflavanic bond of a procyanidin, giving a carbocation

addition of the flavanol takes place onto the flavylium form of the anthocyanin, yielding a colourless compound with the anthocyanin in flavene form. This

or in a colourless compound A(-O-)T with a type-A bond (XIV) [31] (**Figure 3**). As described for the monomeric anthocyanins, these pigments can also occur in a dynamic equilibrium among some molecular forms, mainly the quinoidal base, the flavylium cation and the hemiketal or carbinol pseudobase [30]. Both

 pigments and colourless A(-O-)T have been detected in wines [35]. Dimeric anthocyanins (XVI) consisting of one unit under flavylium cation and the other


further structural rearrangements. After the dehydration, a new heterocyclic pyran ring is formed and the xanthylium structure is generated [17, 37–40]

only flavanols or with anthocyanins is the most well documented reaction in the literature [31, 37, 43–51]. Acetaldehyde is the main aldehyde (90%) present in wines as a result of yeast metabolism during the first stages of alcoholic fermentation, being also produced throughout the wine ageing process from ethanol oxidation [52]. In fortified wines like Port wines, this compound and other aldehydes (propionaldehyde, 2-methylbutyraldehyde, isovaleraldehyde, methylglyoxal, benzaldehyde) are present in higher amounts due to the addition of wine spirit (40–260 mg/L of acetaldehyde) to stop the alcoholic fermentation [53]. Ethyl-linked products, including ethyl-linked flavanols [54, 55] and ethyl-linked anthocyanin-flavanol pigments (XVII) [55] have been detected in wines (**Figure 2**).

(**Figure 3**). However, xanthylium pigments are also proposed to be formed directly

On the other hand, the acetaldehyde-mediated polymerisation between either

shown to occur both in model solution and in wine [56]. The ethyl-linked 8,8-malvidin-3-glucoside dimer was characterised by NMR under biflavylium cation forms [56]. However, physicochemical studies carried out on this pigment showed that the dimer under monoflavylium cation is the most abundant form at wine pH [57]. Another important group of anthocyanin derived pigments formed during ageing, also found in red Port wines, are the pyranoanthocyanins (XIX) (**Figure 3**). Pyranoanthocyanins are a group of anthocyanin-derived pigments [58, 59], which were first discovered in red wine by Cameira-dos-Santos et al. [60].

Pyranoanthocyanins are structurally characterised by the presence of a fourth ring between C-4 and the 5-hydroxyl group of an anthocyanin moiety, differing from each other on the type of group or molecule linked to the C-10 of the new ring [58, 61, 62]. The pyranic ring in pyranoanthocyanins provides protection against the nucleophilic attack from water or bisulphite, increasing their stability [63], making these compounds exceptionally stable pigments towards sulphite bleaching

[34]. In the formation of A<sup>+</sup>

flavene can be oxidised, resulting in a coloured flavylium A<sup>+</sup>

 which reacts with the hydrated form of the anthocyanin (II). This mechanism leads to a colourless compound (T-AOH) which easily dehydrates to the coloured

, XII) or anthocyanin-tannin



formation begins with



**128**

and pH variations. Both anthocyanin-flavanol derived pigments, direct ones and ethyl-linked ones, show less stability during ageing than pyranoanthocyanins. Through the reaction of anthocyanins with acetaldehyde [61, 63], pyruvic acid [58, 64], cinnamic acids [65, 66], acetoacetic acid [64], and procyanidins in the presence of acetaldehyde [67], several different classes of these pigments have been identified in the past decade such as vitisins [58, 59, 61, 68, 69], hydroxyphenyl-pyranoanthocyanins (pinotins) [59, 64, 70–72], methylpyranoanthocyanins [59, 73], vinylflavanol-pyranoanthocyanins [59], portisins [58, 59, 61, 66, 67, 74, 75], and more recently a new family of pyranoanthocyanin dimers [28, 73, 76, 77] (**Table 2**).

Pyruvic acid leads to the major pyranoanthocyanins determined in wines, i.e. carboxy-pyranoanthocyanins (R = COOH), sometimes referred to as vitisin A [58, 59, 61, 68, 69]. In red Port wines, it is the main pigment found during ageing. Due to its particular vinification process, the concentration of vitisin A is very high: 51.2 mg/L for Touriga Nacional Port wines, for example [78]. Indeed, wine fortification after alcoholic fermentation allows greater availability of pyruvic acid [79], which leads to reaching the highest contents shortly after fermentation and during the first year of ageing, followed by a slow decline [80]. After one year of ageing in barrels, the contents decrease by about 15–25% and about 70% after two years, whereas it is not so much important during bottle ageing (9–18%). Romero and Bakker [81] have demonstrated that the addition of pyruvic acid to finished Port wines from four different grape varieties resulted in an increase of malvidin-pyruvic acid adducts. It was also found that the concentration of anthocyanin-pyruvic acid adducts in wines was directly related to the original grape anthocyanin profile; the higher the initial anthocyanin precursor forms, the higher the concentration of corresponding adducts [81–83]. Morata et al. [84] have reported that the yeast strain used in the alcoholic fermentation (inoculated or not) also affects the production of malvidin-3-glucoside-pyruvate, existing a direct relation between the concentration of the pigment and the production of pyruvic acid by the yeast.

Moreover, the content of SO2 in must can also influence the production of malvidin-3-glucoside-pyruvate, since SO2 regulates the concentration of pyruvic acid through the formation of a weak bisulphite addition compound [85].

Romero and Bakker [68] have reported that malvidin-derived pyruvic acids adduct in model solutions provided approximately 11-fold (at pH 3) and 14-fold (at pH 2) more colour than grape anthocyanins.

Flavanol pyranoanthocyanins are formed by the cycloaddition between anthocyanins and 8-vinylflavanol adducts initially derived from the cleavage of ethyl-linked flavanol oligomers [46] or pigments [86, 87]. In red Port wines, pyranoanthocyanin-procyanidin dimers were identified in higher concentrations than the corresponding pyranoanthocyanin-catechins, representing up to 80% of the total pyranomalvidin-flavanols. This postulate is concordant with the fact that procyanidin dimers are more abundant than catechin monomers in grapes and wines from the Douro region [88, 89]. Furthermore, their concentrations decreased in older wines for both malvidin-3-glucoside derived-pigments (10.59 mg/L in 3 year aged wines, 9.16 mg/L in 4 year aged wines and 7.86 mg/L in 6 year aged wines) and associated coumaroyl pigments (6.62, 5.51 and 3.33 mg/L in 3, 4 and 6 year aged wines, respectively).

A second generation of pyranoanthocyanins can be formed by the reaction between a vitisin A and other metabolites. For example, oxovitisins (XX) are neutral yellowish pyranone structures involving the nucleophilic attack of water at the C-10 position of vitisin A [90].


#### **Table 2.**

*Pyranoanthocyanins identified in wines and precursors.*

In 2003 Mateus et al. [74] reported a new group of pyranoanthocyaninsvinylpyranoanthocyanins-which were named portisins (XXI), because of their occurrence in aged red Port wine [61, 67, 74, 75], **Figure 3**. The structure of these compounds consists of a pyranoanthocyanin moiety linked through a vinyl bridge to a flavanol or phenol unit. Their pathway of formation involves the carboxypyranoanthocyanins and vinylphenolic compounds. The first of these compounds

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*DOI: http://dx.doi.org/10.5772/intechopen.94900*

533 and 540 nm at aqueous pH 1) [91].

blue pigments were found in a 9 year aged Port wine [73].

*3.1.2 Aroma composition and sensory development*

flavour', 'Spicy sensation' and 'Persistence' [98].

reported in the literature arise from reaction of 8-vinylflavanol with carbon C-10 of the carboxypyranoanthocyanins, followed by loss of a formic acid group yielding the vinyl bridge. Portisins have been shown to have very high colouring capacity, much higher than that of their anthocyanin or pyruvic acid adduct counterparts [91–93]. Later, other portisins (B type) were detected in aged Port wines. In these, the flavanol moiety is replaced by a phenolic moiety with different hydroxylation and methoxylation patterns [61, 67, 74, 75]. These compounds were reported to result from the reaction of carboxypyranoanthocyanins with vinylphenols and cinnamic acids, following a mechanism similar to that of vinylflavanols and involving a further decarboxylation. However, the colour features of these portisins are different from those of the portisins discussed above because they have a λmax hypsochromically shifted from that of vinylpyranoanthocyanin-catechins, and are only slightly affected by the substitution pattern of the new phenolic ring (between

The condensation between A-type vitisins and methylpyroanthocyanins results in the formation of pyranoanthocyanin dimers (XXII), **Figure 3**. These turquoise

The volatile compounds present in Port wines have their origin on the grapes used, are produced during the alcoholic fermentation and being also added as part of the wine spirit used for Port wine production that contains trace volatile compounds such as esters (ethyl hexanoate, ethyl octanoate, ethyl decanoate) and terpenes (α-terpineol, linalool) that can affect the quality of the Port wines, contributing to a fruity, balsamic and spicy aroma [94]. In addition, wine spirits are rich in aldehydes such as acetaldehyde, propionaldehyde, isovaleraldehyde, isobutyraldehyde, and benzaldehyde [94]. The volatile profile of young Port wines is significantly different from that of aged Tawny Port wines or bottle-aged Port wines. Producers blend wines from several vintages and vineyards to produce wines with a consistent character. The final aroma character of the Port wine is to a considerable extent determined by the processes that take place during the oxidative ageing process of these wines, such as oxidation, carbohydrate degradation, formation and hydrolysis of esters, formation of acetals and to a lesser extent extraction of components from wood [11]. More than 200 volatile components have been detected in Port wines, 141 of which have been entirely or partially identified, however, the sensory importance of the various groups of volatile compounds does not entirely explain the sensory properties of Ruby or Tawny Port wines [95]. For the Ruby Port wine sensory profile, the attributes are 'Ruby', 'Persistence', 'Red fruits', 'Fruity flavour', 'Astringency' and 'Floral' were dominant, whereas in the White Port wine attributes like 'Honey', 'Sweet taste', 'Alcoholic sensation', 'Balance', 'Acid taste' and 'Moscatel' are the ones that better characterise these wines, Tawny Port wines are characterised by the attributes 'Dried fruits flavour', 'Dried fruits', 'Spices', 'Wood' and 'Sweet/Honey' [96, 97]. The Pink Port wines sensory attributes are characterised by the attributes 'Red fruit aroma', 'Body', 'Fruit aroma', 'Fruity

Norisoprenoids have been found to contribute significantly to the aroma of young and aged Port wines [76, 99–101]. In a one year aged Port wine produced from Touriga Franca and Touriga Nacional grape varieties the norisoprenoid, 2,6,6-trimethylcyclohex-2-ene-1,4-dione, described as having sweet honey aroma, was identified by Rogerson et al. [102]. In a young Port wine produced from Tinto Cão and Tinta Barroca grape varieties, Rogerson et al. [103] identified the 1,3-dimethoxybenzene

## *Port Wine: Production and Ageing DOI: http://dx.doi.org/10.5772/intechopen.94900*

*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

R1 and R2 = OCH3; R3 = Glucose

(I) In **Figure 3**

(XIX) In **Figure 3**

Non-substituted

R4 = COOH

(Vitisin A)

R4 = CH3

R4 = COCH3

R4 = flavanol

(XX) In **Figure 3** Pyranone-anthocyanins

(XXI) In **Figure 3** R6 = hydroxyphenyl

Vinylphenyl-pyroanthocyanins

Vinylflavanol-pyroanthocyanins

(oxovitisins)

(Portisin B)

R6 = flavanol

(Portisin A)

**Table 2.**

(XXII) in **Figure 3**

R4 = hydroxyphenyl

R4 = dihydroxyphenyl

pyroanthocyanins (Vitisin B)

Carboxypyroanthocyanins

R4 = H

**Pyroanthocyanins Precursors References**

Malvidin-3-glucoside (Oenin) [13–15]

Methylpyroanthocyanins Oenin+acetoacetic acid or acetone [59, 73]

Acetylpyroanthocyanins Oenin+diacetyl [8, 28–33]

Hidroxyphenylpyroanthocyanins Oenin+*p*-coumaric acid or vinylphenol [59, 64, 70–72]

Pinotin A Oenin + caffeic acid or vinylcatechol [59, 64, 70–72]

flavan-3-ols + acetaldehyde

Carboxypyroanthocyanins + water [90]

Carboxypyroanthocyanins+hydroxyci nnamic acids or vinylphenols

Carboxypyroanthocyanins + vinylflavanols or flavan-3-ols and

methylpyroanthocyanins

acetaldehyde

Pyroanthocyanins dimers Carboxypyroanthocyanins +

*Pyranoanthocyanins identified in wines and precursors.*

Flavanol-pyroanthocyanins Oenin+vinylflavanols or

Oenin+acetaldehyde [58–61, 68, 69]

Oenin+pyruvic acid [58–61, 68, 69]

[59]

[58, 59, 61, 66, 67, 74, 75]

[58, 59, 61, 66, 67, 74, 75]

[28, 73, 76, 77]

In 2003 Mateus et al. [74] reported a new group of pyranoanthocyaninsvinylpyranoanthocyanins-which were named portisins (XXI), because of their occurrence in aged red Port wine [61, 67, 74, 75], **Figure 3**. The structure of these compounds consists of a pyranoanthocyanin moiety linked through a vinyl bridge to a flavanol or phenol unit. Their pathway of formation involves the carboxypyranoanthocyanins and vinylphenolic compounds. The first of these compounds

**130**

reported in the literature arise from reaction of 8-vinylflavanol with carbon C-10 of the carboxypyranoanthocyanins, followed by loss of a formic acid group yielding the vinyl bridge. Portisins have been shown to have very high colouring capacity, much higher than that of their anthocyanin or pyruvic acid adduct counterparts [91–93]. Later, other portisins (B type) were detected in aged Port wines. In these, the flavanol moiety is replaced by a phenolic moiety with different hydroxylation and methoxylation patterns [61, 67, 74, 75]. These compounds were reported to result from the reaction of carboxypyranoanthocyanins with vinylphenols and cinnamic acids, following a mechanism similar to that of vinylflavanols and involving a further decarboxylation. However, the colour features of these portisins are different from those of the portisins discussed above because they have a λmax hypsochromically shifted from that of vinylpyranoanthocyanin-catechins, and are only slightly affected by the substitution pattern of the new phenolic ring (between 533 and 540 nm at aqueous pH 1) [91].

The condensation between A-type vitisins and methylpyroanthocyanins results in the formation of pyranoanthocyanin dimers (XXII), **Figure 3**. These turquoise blue pigments were found in a 9 year aged Port wine [73].
