抗壞血酸在乙醇溶液中降解之研究

Degradation of Ascorbic Acid in Ethanolic Solutions

蔡依瑾(Yi-Chin Tsai)

指導教授 ： 吳瑞碧

國立臺灣大學/生物資源暨農學院/食品科技研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.03103

摘要

為瞭解抗壞血酸於乙醇溶液中的穩定性，本研究利用 0-40 % 酒精濃度的抗壞血酸模式溶液進行探討。反應動力學結果顯示，在45 ℃ 下儲藏，抗壞血酸於酒精溶液中之降解速率隨著乙醇濃度的提高而上升，且抗壞血酸之降解為一級反應 (first-order reaction)。酒精模式溶液中抗壞血酸之降解活化能介於9.71-3.33 (kcal/mole) 之間，且與酒精濃度成劑量關係增加。2-furoic acid 、呋喃醛 (furfural) 和 3-hydroxy-2-pyrone (3OH2P) 為抗壞血酸主要之降解產物，隨著模式溶液酒精濃度的提高其生成量逐漸減少；而抗壞血酸模式溶液於儲藏過程中的褐變情形並不明顯。由生成的產物分析結果推測，抗壞血酸在酒精溶液中主要是走好氧裂解途徑。
水活性與酸鹼值為影響抗壞血酸降解的主要因子。抗壞血酸於 pH 2.6 酒精模式溶液中的降解趨勢、降解產物與褐變情形均與未調整酸鹼值之結果相類似，表示酸鹼值並非是造成高酒精濃度中抗壞血酸降解速率增加、劣解產物降低的主要因素。在 pH 4.6 的酒精模式溶液中，抗壞血酸之降解亦隨著酒精濃度的增加而增加，且降解產物和褐變程度亦隨酒精濃度的增加而增加。
以甘油配製成與酒精模式溶液相同水活性之甘油模式溶液，並經酸鹼值調整至 2.6 後，儲藏於 45 ℃ 下，結果顯示隨著甘油濃度增加 (相當於高酒精濃度)，模式溶液水活性降低，抗壞血酸之降解卻越快，此結果與前述實驗結果不同，表示水活性亦非是高酒精濃度下抗壞血酸降解加速的主要因素。

關鍵字

抗壞血酸 ； 降解 ； 動力學 ； 乙醇 ； 褐變

並列摘要

For understanding the effect of ethanol on ascorbic acid degradation, 0 - 40 % ethanol concentrations model solution was used. Results from kinetic study showed that the degradation rate constant of ascorbic acid is increased with the increase of ethanol concentration and the degradation of ascorbic acid in ethanolic solutions followed first-order reaction. At 45℃ incubation temperature, the activation energies (Ea) of the ascorbic acid degradation products in 0-40 % ethanolic solutions are between 9.71-3.33 (kcal/mole) with a dose manner. 2-furoic acid and 3-hydroxy-2-pyrone were the major degradation products in ascorbic acid ethanolic model solutions. The production of the two compounds decreased with the increase of ethanol concentrations. According to the above results, we postulate that the aerobic degradation pathway dominates over the anaerobic pathway for ascorbic acid in ethanolic model solutions.
Water activity (aw) and pH value were main factors affecting the ascorbic acid degradation. The results revealed that degradation rate of ascorbic acid in pH 2.6 buffered ethanolic solutions were much faster than in the ethanolic solutions without pH controlling. The formation of degradation products and the browning index of ascorbic acid in pH 2.6 buffered ethanolic solutions were similar to that in the ethanolic model solutions without pH controlling, too. We propose that pH is not the sole factor affecting the ascorbic acid degradation rate in high ethanol concentration solutions. In pH 4.6 buffered ethanolic solutions, the degradation of ascorbic acid, the formation of the degradation products and the browning of the solutions also increased with the increase of ethanol concentration.
Glycerol was used for adjusting to the similar aw of ascorbic acid ethanolic model solutions. The solutions were buffered at pH 2.6 and stored at 45℃. The result shows that degradation rate of ascorbic acid is much faster in buffered glycerol model solutions with higher aw than that in ethanolic model solutions. We postulate that water activity is not the major factor affecting the ascorbic acid degradation in high ethanol concentration solutions.

並列關鍵字

Ascorbic acid ； degradation ； kinetic ； ethanol ； browning

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