桃汁热处理过程中非酶褐变动力学研究

桃汁在热处理过程中极易发生褐变反应，通常将褐变度和色值L*作为评价桃汁褐变程度的指标。通过测定和分析桃汁在热处理（80、90 ℃和100 ℃）过程中的相关指标发现，桃汁的褐变度分别上升了0.185、0.221和0.276，L*值分别下降了4.22、5.74和7.53，Chroma值和Hue值在热处理过程中逐渐变小，褐变指数不断增大；用零级、一级和联合动力学模型拟合各指标的动态变化的研究发现，联合动力学模型可以更好地表示褐变度和色值的动态变化（R2＞0.823）；热处理过程中VC含量不断减少，符合零级反应动力学模型（R2＞0.894）；5-羟甲基糠醛含量不断增加，符合联合动力学模型（R2＞0.905），且在各个热处理的温度条件下5-羟甲基糠醛的生成与褐变度的变化表现出二次项关系（R2＞0.940）。

Kinetic Study of Non-enzymatic Browning of Peach Juice during Thermal Treatments

Non-enzymatic browning easily takes place during thermal treatment of peach juice. Browning degree and the
colour parameter L* are usually used as indexes to evaluate non-enzymatic browning. The indexes during thermal processing
at different temperatures 80, 90 ℃ and 100 ℃ for peach juice were investigated. The results showed that with increasing
temperature, the browning degree was increased by 0.185, 0.221 and 0.276, whereas the L* value was decreased by 4.22,
5.74 and 7.53, respectively. Both the chroma value and Hue angle were gradually decreased. The browning index (BI) was
increased as the temperature increased. Various kinetic models including zero-order kinetic, first-order kinetic and combined
kinetic models were employed to fit the experimental data. The results showed that the combined kinetic model was a better
one for describing the dynamic changes in browning degree and colour value, as compared to the other two models (R2＞
0.823). Furthermore, the declined vitamin C content during thermal processing could be accurately described by the zeroorder
kinetic model (R2＞0.894). Meanwhile, the combined kinetic model (R2＞0.905) could properly express the gain of
5-hydroxymethylfurfural contents. The relationship between 5-hydroxymethylfurfural and browning degree was satisfactorily
fitted by means of quadratic model (R2＞0.940) at three different temperatures.