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Estudo da cinética de extração de polifenóis totais e taninos de diferentes madeiras durante o estágio de vinhos
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O presente trabalho teve como principal objetivo o estudo da lei cinética da reação de extração de polifenóis totais e de taninos, contribuindo para uma compreensão mais aprofundada da dinâmica deste processo em vinhos brancos em contacto com aparas de madeira. Paralelamente, avaliou-se a influência de fatores enológicos e tecnológicos na extração de compostos fenólicos e nas características cromáticas do vinho, em condições distintas de envelhecimento. Para tal, foram estudadas combinações de dois teores alcoólicos (11% e 15% v/v), dois valores de pH (3,2 e 3,5), dois tipos de madeira (carvalho francês e americano) e diferentes intensidades de tosta do carvalho francês (sem tosta, ligeira, média e forte). De forma geral, os resultados demonstraram que o teor alcoólico mais baixo (11%) favoreceu extrações mais elevadas e consistentes ao longo do tempo, ainda que acompanhado por uma menor estabilidade cromática. Em contrapartida, o teor alcoólico de 15% potenciou a
solubilização de compostos menos polares, resultando em perfis de extração mais rápidos, mas também mais oscilantes. Relativamente ao pH, verificou-se que o valor de 3,2 conduziu a valores mais instáveis, com quebras abruptas, enquanto pH 3,5 originou extrações mais progressivas e equilibradas, favorecendo a acumulação gradual de compostos fenólicos. No que respeita à madeira, o carvalho francês, em especial na condição de tosta média, apresentou a capacidade de promover extrações equilibradas e consistentes, garantindo simultaneamente complexidade e estabilidade. O carvalho americano mostrou perfis mais irregulares, com extrações intensas, mas pouco sustentadas, provavelmente devido à sua maior porosidade e reatividade. A madeira de carvalho francês sem tosta destacou-se pela preservação de elagitaninos e pela libertação contínua de polifenóis, reforçando a sua relevância em vinhos destinados a maior longevidade. Em contraste, a tosta forte limitou a acumulação de compostos, consequência da degradação térmica e da carbonização superficial
da madeira. A análise colorimétrica confirmou a elevada luminosidade dos vinhos (L* entre 94,890 e 98,778), típica de vinhos brancos jovens, bem como tonalidades predominantemente esverdeadas (a* negativo), associadas à presença de flavonoides. As variações observadas no parâmetro b* (5,80–11,80) refletiram diferentes graus de evolução cromática, embora sem impacto visual significativo a olho nu, revelando uma notável estabilidade global Do ponto de vista cinético, concluiu-se que as reações de extração de polifenóis totais e de taninos podem ser descritas por um modelo de primeira ordem. No caso dos polifenóis totais, verificaram-se coeficientes de correlação elevados (R² > 0,9 em vários ensaios), confirmando a robustez do modelo, como na amostra 16 (R² = 0,9829). Para os taninos, os coeficientes foram, em geral, mais baixos, mas ainda assim evidenciaram uma predominância da primeira ordem, com valores relevantes como o da amostra 6 (R² = 0,9087). Os valores obtidos para as constantes de velocidade (k) revelaram que a extração de taninos foi mais rápida
(7,01 × 10⁻⁴ – 1,03 × 10⁻³ h⁻¹), em comparação com os polifenóis totais (3,51 × 10⁻⁵ – 7,41 × 10⁻⁴ h⁻¹), embora menos estáveis.
The main objective of this study was to determine the kinetic law of the extraction reaction of total polyphenols and tannins, contributing to a deeper understanding of the dynamics of this process in white wines in contact with wood chips. At the same time, the influence of oenological and technological factors on the extraction of phenolic compounds and the chromatic characteristics of wine under different aging conditions was evaluated. To this end, combinations of two alcohol contents (11% and 15% v/v), two pH values (3.2 and 3.5), two types of wood (French and American oak), and different intensities of French oak toasting (no toasting, light, medium, and heavy) were studied. In general, the results showed that the lower alcohol content (11%) favors higher and more sustained extractions over time, although accompanied by lower chromatic stability. In contrast, the 15% alcohol content enhanced the solubilization of less polar compounds, resulting in faster but also less regular extraction profiles. Regarding pH, it was found that a value of 3.2 led to more unstable curves with abrupt breaks, while pH 3.5 resulted in more progressive and balanced extractions, favoring the gradual accumulation of phenolic compounds. About wood, French oak, especially when medium toasted, showed the ability to promote balanced and consistent extractions, while ensuring complexity and stability. American oak showed more irregular profiles, with intense but unsustained extractions, probably due to its greater porosity and reactivity. Untoasted French oak stood out for its preservation of ellagitannins and continuous release of polyphenols, reinforcing its relevance in wines intended for longer aging. In contrast, heavy toasting limited the accumulation of compounds, a consequence of thermal degradation and surface charring of the wood. Colorimetric analysis confirmed the high brightness of the wines (L* between 94.890 and 98.778), typical of young white wines, as well as predominantly greenish tones (negative a*), associated with the presence of flavonoids. The variations observed in the b* parameter (5.80–11.80) reflected different degrees of chromatic evolution, although without significant visual impact to the naked eye, revealing remarkable overall stability. From a kinetic point of view, it was concluded that the extraction of total polyphenols and tannins can be consistently described by a first-order model. In the case of total polyphenols, high correlation coefficients were found (R² > 0.9 in several tests), confirming the robustness of the model, as in bottle 16 (R² = 0.9829). For tannins, the coefficients were generally lower, but still showed a predominance of the first order, with relevant values such as that of bottle 6 (R² = 0.9087). The rate constants (k) revealed that tannin extraction was faster (7.01 × 10⁻⁴ – 1.03 × 10⁻³ h⁻¹) compared to total polyphenols (3.51 × 10⁻⁵ – 7.41 × 10⁻⁴ h⁻¹), although less stable.
The main objective of this study was to determine the kinetic law of the extraction reaction of total polyphenols and tannins, contributing to a deeper understanding of the dynamics of this process in white wines in contact with wood chips. At the same time, the influence of oenological and technological factors on the extraction of phenolic compounds and the chromatic characteristics of wine under different aging conditions was evaluated. To this end, combinations of two alcohol contents (11% and 15% v/v), two pH values (3.2 and 3.5), two types of wood (French and American oak), and different intensities of French oak toasting (no toasting, light, medium, and heavy) were studied. In general, the results showed that the lower alcohol content (11%) favors higher and more sustained extractions over time, although accompanied by lower chromatic stability. In contrast, the 15% alcohol content enhanced the solubilization of less polar compounds, resulting in faster but also less regular extraction profiles. Regarding pH, it was found that a value of 3.2 led to more unstable curves with abrupt breaks, while pH 3.5 resulted in more progressive and balanced extractions, favoring the gradual accumulation of phenolic compounds. About wood, French oak, especially when medium toasted, showed the ability to promote balanced and consistent extractions, while ensuring complexity and stability. American oak showed more irregular profiles, with intense but unsustained extractions, probably due to its greater porosity and reactivity. Untoasted French oak stood out for its preservation of ellagitannins and continuous release of polyphenols, reinforcing its relevance in wines intended for longer aging. In contrast, heavy toasting limited the accumulation of compounds, a consequence of thermal degradation and surface charring of the wood. Colorimetric analysis confirmed the high brightness of the wines (L* between 94.890 and 98.778), typical of young white wines, as well as predominantly greenish tones (negative a*), associated with the presence of flavonoids. The variations observed in the b* parameter (5.80–11.80) reflected different degrees of chromatic evolution, although without significant visual impact to the naked eye, revealing remarkable overall stability. From a kinetic point of view, it was concluded that the extraction of total polyphenols and tannins can be consistently described by a first-order model. In the case of total polyphenols, high correlation coefficients were found (R² > 0.9 in several tests), confirming the robustness of the model, as in bottle 16 (R² = 0.9829). For tannins, the coefficients were generally lower, but still showed a predominance of the first order, with relevant values such as that of bottle 6 (R² = 0.9087). The rate constants (k) revealed that tannin extraction was faster (7.01 × 10⁻⁴ – 1.03 × 10⁻³ h⁻¹) compared to total polyphenols (3.51 × 10⁻⁵ – 7.41 × 10⁻⁴ h⁻¹), although less stable.
Descrição
Palavras-chave
White wine Phenolic compounds Aging in wood Extraction kinetics Alcohol content Type of wood and toast level Vinho branco Compostos fenólicos Envelhecimento em madeira Cinética de extração Teor alcoólico Tipo de madeira e intensidade de tosta