红枣汁中维生素C热降解的动力学研究

Thermal degradation kinetics of vitamin C in jujube juice

为了了解加热温度对红枣汁中维生素C含量变化的影响,降低红枣汁在加工过程中维生素C的损失,该文以红枣澄清汁为材料,采用可逆的一级反应模型研究了不同加热温度下还原型维生素C(AA)的降解规律并推导出氧化型维生素C(DHAA)含量变化的数学模型。在此基础上利用Arrhenius方程计算得到AA和DHAA的降解反应活化能。结果表明,在303,313,323,333,343K温度条件下,可逆的一级反应模型适用于表达红枣汁中AA的降解规律,非线性回归决定系数r2均大于0.98。DHAA的数学模型也能较好地预测DHAA在红枣汁中的含量变化规律。在不同的加热温度下,AA与DHAA均能发生降解反应,但DHAA的降解速率较AA低,DHAA的降解主要发生在AA的降解反应达到平衡之后。AA热降解反应活化能较低,表明红枣汁中的AA对热处理较敏感。该研究为优化红枣汁的加工工艺、提高红枣汁的品质提供理论依据。

In order to investigate the effect of temperature on the vitamin C in jujube juice and decrease the loss of vitamin C in the processing of jujube juice, the thermal degradation kinetics of Ascorbic Acid（AA） at 303, 313, 323, 333 and 343 K in the clarified jujube juice were investigated, and a mathematical model to predict Dehydroascorbic Acid（DHAA） concentration was also established. Activation energies of AA and DHAA degradation were calculated by Arrhenius equation. The results showed that the loss of AA at each temperature followed the reversible first-order kinetic model and all r-squared values were higher than 0.98. The kinetic model of DHAA was fitted to its degradation in jujube juice. Both AA and DHAA in the jujube juice decreased with increasing temperature, however, the rate of AA degradation was higher than that of DHAA for its low activation energy, and degradation of DHAA occurred after AA being in equilibrium. The present study can be applied to optimize the processing technology of jujube juice and improve its quality.