花青素在乙醇溶液中顏色表現之研究

Abstract

本實驗以不同乙醇濃度還原酒及花青素模式溶液，觀察乙醇濃度對花青素顏色及呈色安定性之影響，並探討可能之反應機制。 由實驗結果得知，不同乙醇濃度還原酒之酸鹼值，隨著乙醇濃度的增加而增加，並呈二次關係 (quadratic relation)。由於酸鹼值之變化，改變花青素之結構分佈，影響酒液顏色及呈色安定性。提高酒液中之乙醇濃度，將有助於減緩花青素之copigmentation及self-association，進而減緩花青素之聚合反應，降低沉澱量產生，並提高酒液之呈色安定性。 提高模式溶液之乙醇濃度，亦產生明顯的向紅效應 (bathochromic shift)。乙醇濃度越高，偏移越大。依粒徑及質譜分析結果推測，乙醇分子可能與花青素分子有交互作用，並產生花青素衍生物。當乙醇濃度改變時，此交互作用亦發生改變，導致光譜移動。粒徑分析結果亦支持花青素之self-association受乙醇濃度影響之說法，當提高模式溶液之乙醇濃度時，由於self-association作用力減弱，因此釋放出更多的游離flavylium cation及/或quinoidal base，改變花青素之結構分佈，影響花青素呈色。 不同乙醇濃度malvidin-3-glucoside模式溶液之降解反應為一次反應 (first-order reaction)，其降解速率隨著乙醇濃度及反應溫度的提高而增加。

Reconstituted wines and anthocyanin model solutions with different ethanol concentrations were used to investigate the effect of ethanol on the color phenomena of anthocyanin and then the possible mechanism was proposed. Results show that the pH of reconstituted wines increased with increment of ethanol concentration following a quadratic relation. The equilibrium among different forms of anthocyanin was affected by the increase in pH value then the color and stability of wine. An increase in ethanol concentration in wine decreases the degrees of copigmentation, self-association, polymerization and precipitate formation then increased the color stability of wine. The occurrence of bathochromic shift upon presence of ethanol increases with ethanol concentration. The results of particle size distribution and Mass spectra indicated that ethanol molecule could react with anthocyanin molecule and produced an anthocyanin adduct. This interaction changes with ethanol concentration and changes the spectra. The results of particle size distribution also proved that the self-association of anthocyanin was affected by ethanol concentration. The extent of self-association decreased with an elevated ethanol concentration in model solution and can be attributed to the increase in the contents of free flavylium cations and/or quinonoidal base that affects the equilibrium among different forms and color of anthocyanin. The degradation of malvidin-3-glucoside follows apparent first order kinetics, and accelerates with the increase in ethanol concentration and temperature.