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Contribution to the knowledge of Port Wine oxidative ageing process: study of chromatic characteristics and aroma profile of Tawny and White Port Wines
| Summary: | White (WPW) and Tawny Port wines (TPW) are two of the most important Port wines styles produced in the Douro Demarcated Region, made from authorised white and red grape varieties where after a short fermentation period is fortified with non-rectified wine spirit up to 20% of ethanol and aged in small used oak barrels (~ 600 L) for at least three years. These conditions allow the contact with oxygen, and therefore, these wines are aged under oxidative conditions. Port wines with indication of age (IAC) are one of the most important categories of WPW and TPW. These are blend wines made up by older and newer aged Port wines to obtain the sensory characteristics of a WPW or TPW that would been aged for the time indicated. The certification of these categories is made by the sensory panel of the “Instituto dos Vinhos do Douro e Porto”. Colour of the different styles of Port wines and IAC are a distinctive quality parameter dependent on the grapes used, ageing process, and time. The impact of the phenolic composition of the different Port wine styles and IAC is largely unknown. We characterised the chromatic characteristics (CIEL*a*b*) and relation with the phenolic composition including monomeric, small (SPP) and large polymeric pigments (LPP) and tannins of WPW, TPW and Ruby Port wines (RPW) and evaluated the feasibility of its use for their discrimination. Port wine styles can be discriminated using the chromatic characteristics. WPW presented the highest L* values, RPW presented the highest a* values and TPW presented the highest b* values. Their chromatic characteristics were related to their pigment/phenolic composition. RPW contained the highest levels of phenolic compounds. For all Port wines the majority of the total pigments at 520 nm and 420 nm are presented as polymeric pigments (PP, 71%). On the other hand, RPW and TPW presented the PP as LPP, higher. The same trend was observed for SPP 420 nm and LPP 420 nm. The more oxidative ageing of TPW when compared to RPW, results in wines with lower levels of pigment/phenolic compounds, this decrease increasing with the IAC of TPW resulting in an increase in L* and b* and decrease in a*. On the contrary for WPW the pigments are developed and increased with the IAC, resulting in a decrease in the L* value and increase in a* and b* values. The higher b* values, corresponding to the brownish/yellowish colour of TPW and WPW belonging to higher IAC seems to be related to the sugar browning than oxidative change in phenolic compounds, although this phenomenon is important for decreasing the red colour (a* value) of TPW for the higher IAC. The aroma profile of TPW and WPW with increasing IAC was determined to study the similarities and differences in the oxidative ageing of these two related but different matrixes, being quantified thirty-one and twenty-eight aroma compounds, respectively. Sotolon increased for both wine styles being important for the aroma of Port wines with higher IAC, where it presented an olfactory activity value (OAV) higher than unity, nevertheless, ethyl hexanoate, ethyl octanoate, ethyl decanoate had also OAVs >1, especially in TPW where their concentration increased with increasing IAC, and decrease in importance for WPW, as they decrease for higher IAC. TDN and -damascenone appear to have also an important contribution to the aroma due to their very low odour threshold. The differences in aroma evolution pattern observed for these two wine styles can be due to the differences in the wine matrix composition preventing the loss of aroma compounds by evaporation in TPW as that observed for the WPW with increasing IAC. Sotolon, HMF, and -ketobutyric acid increased with the increase IAC with small differences for WPW and TPW, and that there is probably a common origin of these three compounds. Results obtained from model systems allowed to support the hypothesis that fructose is the main precursor of sotolon, HMF and -ketobutyric acid, that increase for TPW and WPW with increasing IAC. The presence of amino acids reduced the amount of sotolon and increased the amount of -ketobutyric acid and HMF formed from fructose. On the other hand, metal catalysts (iron and copper) reduced Sotolon yield but increased the b* value of Port wine like models. These results show that in Port wines obtained by oxidative ageing, either made from white or red grape varieties, fructose caramelisation is the main pathway for sotolon formation and also -ketobutyric acid and HMF, although for these last two the Maillard reaction is the most efficient pathway. |
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| Authors: | Nunes, Fernando; Cosme, Fernanda |
| Subject: | White Port wine Tawny Port wine |
| Year: | 2024 |
| Country: | Portugal |
| Document type: | doctoral thesis |
| Access type: | Restricted |
| Associated institution: | Repositório da UTAD, DSpace at My University, Repositório Institucional da UTAD |
| Language: | English |
| Origin: | Repositório da UTAD |
| Summary: | White (WPW) and Tawny Port wines (TPW) are two of the most important Port wines styles produced in the Douro Demarcated Region, made from authorised white and red grape varieties where after a short fermentation period is fortified with non-rectified wine spirit up to 20% of ethanol and aged in small used oak barrels (~ 600 L) for at least three years. These conditions allow the contact with oxygen, and therefore, these wines are aged under oxidative conditions. Port wines with indication of age (IAC) are one of the most important categories of WPW and TPW. These are blend wines made up by older and newer aged Port wines to obtain the sensory characteristics of a WPW or TPW that would been aged for the time indicated. The certification of these categories is made by the sensory panel of the “Instituto dos Vinhos do Douro e Porto”. Colour of the different styles of Port wines and IAC are a distinctive quality parameter dependent on the grapes used, ageing process, and time. The impact of the phenolic composition of the different Port wine styles and IAC is largely unknown. We characterised the chromatic characteristics (CIEL*a*b*) and relation with the phenolic composition including monomeric, small (SPP) and large polymeric pigments (LPP) and tannins of WPW, TPW and Ruby Port wines (RPW) and evaluated the feasibility of its use for their discrimination. Port wine styles can be discriminated using the chromatic characteristics. WPW presented the highest L* values, RPW presented the highest a* values and TPW presented the highest b* values. Their chromatic characteristics were related to their pigment/phenolic composition. RPW contained the highest levels of phenolic compounds. For all Port wines the majority of the total pigments at 520 nm and 420 nm are presented as polymeric pigments (PP, 71%). On the other hand, RPW and TPW presented the PP as LPP, higher. The same trend was observed for SPP 420 nm and LPP 420 nm. The more oxidative ageing of TPW when compared to RPW, results in wines with lower levels of pigment/phenolic compounds, this decrease increasing with the IAC of TPW resulting in an increase in L* and b* and decrease in a*. On the contrary for WPW the pigments are developed and increased with the IAC, resulting in a decrease in the L* value and increase in a* and b* values. The higher b* values, corresponding to the brownish/yellowish colour of TPW and WPW belonging to higher IAC seems to be related to the sugar browning than oxidative change in phenolic compounds, although this phenomenon is important for decreasing the red colour (a* value) of TPW for the higher IAC. The aroma profile of TPW and WPW with increasing IAC was determined to study the similarities and differences in the oxidative ageing of these two related but different matrixes, being quantified thirty-one and twenty-eight aroma compounds, respectively. Sotolon increased for both wine styles being important for the aroma of Port wines with higher IAC, where it presented an olfactory activity value (OAV) higher than unity, nevertheless, ethyl hexanoate, ethyl octanoate, ethyl decanoate had also OAVs >1, especially in TPW where their concentration increased with increasing IAC, and decrease in importance for WPW, as they decrease for higher IAC. TDN and -damascenone appear to have also an important contribution to the aroma due to their very low odour threshold. The differences in aroma evolution pattern observed for these two wine styles can be due to the differences in the wine matrix composition preventing the loss of aroma compounds by evaporation in TPW as that observed for the WPW with increasing IAC. Sotolon, HMF, and -ketobutyric acid increased with the increase IAC with small differences for WPW and TPW, and that there is probably a common origin of these three compounds. Results obtained from model systems allowed to support the hypothesis that fructose is the main precursor of sotolon, HMF and -ketobutyric acid, that increase for TPW and WPW with increasing IAC. The presence of amino acids reduced the amount of sotolon and increased the amount of -ketobutyric acid and HMF formed from fructose. On the other hand, metal catalysts (iron and copper) reduced Sotolon yield but increased the b* value of Port wine like models. These results show that in Port wines obtained by oxidative ageing, either made from white or red grape varieties, fructose caramelisation is the main pathway for sotolon formation and also -ketobutyric acid and HMF, although for these last two the Maillard reaction is the most efficient pathway. |
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