Kinetic Model of Changes in the Main Chemical Composition of Yellow Tea during Piling
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Abstract:
Changes in the color difference and main chemical composition of yellow tea, along with piling time, were studied at different temperatures and different water content. The key chemical components causing the yellowing of yellow tea are chlorophyll a, epigallocatechin gallate (EGCG), and epicatechin gallate (ECG), and kinetic models for the relationship of chlorophyll a, EGCG, and ECG with piling time and temperature were established, so as to predict the degree of yellowing during the piling process. The results showed that a zero-order kinetic equation could provide a good fit for chlorophyll a, EGCG, and ECG. The relative error of the model predicted value and actual value was less than 5%, indicating that the model was effective. The reaction rate constant K (reaction rate) values for the prediction model were calculated under various conditions, and the results indicated that with increasing temperature and moisture content, the K values of chlorophyll a, EGCG, ECG increased gradually. Nonlinear fitting of reaction rate constant and temperature were carried out using the Arrhenius equation, and the Ea (activation energy) and A (frequency factor) of chlorophyll a, EGCG, and ECG were obtained. Under the same conditions, the reaction of chlorophyll a was most likely to occur, followed by those of ECG and EGCG.
