# Formation Mechanisms and Kinetic Modeling of Key Aroma Compounds During Qidan Tea Roasting
## 3 Results and Discussion
### Establishment of Maillard Reaction Model and Kinetic Equation  
Taking theanine, glutamic acid, and glucose as the research objects, the accuracy and universality of the kinetic equations were verified, and the corresponding Maillard reaction system was established to study the interactions between these substances and the generation of aroma substances under different roasting conditions. Based on the experimental results, the most representative substances were selected to fit the kinetic equations. As can be seen from Figure 2, benzaldehyde, as a representative aldehyde, shows a significant correlation between its content change and roasting conditions. With the increase of heating time, the amount of benzaldehyde increased continuously, indicating that longer heating time is favorable to the production of this substance; at the same time, the increase of heating temperature will directly promote the increase of benzaldehyde content, reflecting the accelerating effect of temperature on the reaction process. From the fitting results of the kinetic model, the generation of benzaldehyde at 100 \({}^{\circ}\)C conformed to the zero-order kinetic equation, which indicated that the reaction rate at this temperature was independent of the concentration of the reactants, and might be limited by other rate-control steps; whereas, the first-order kinetic equations were followed at 110 \({}^{\circ}\)C and 120 \({}^{\circ}\)C, which indicated that the reaction rate and the concentration of the reactants were linearly correlated, and that high temperature environment significantly enhanced the reaction activity. In a word, the high temperature conditions were more favorable for the formation of benzaldehyde, and the heating temperature was positively correlated with the rate of formation. The rate of benzaldehyde formation was sluggish at low temperatures but was greatly accelerated at high temperatures. In this study, the synergistic mechanism of temperature-time parameters on the formation of the products of the Melad reaction was revealed by systematically monitoring the generation pattern of typical pyrazines under different heat treatment conditions. As shown in Figure 2 and Table 4, the generation of 2-methylpyrazine showed typical temperature-dependent characteristics. The compound was not detected in the initial stage (0 h) and in the low temperature treatment group (100 \({}^{\circ}\)C and 110 \({}^{\circ}\)C treatment for 2 h). When the temperature reached 120 \({}^{\circ}\)C, 2-methylpyrazine began to be formed, and its kinetic curve showed a slow accumulation period in the first 4 h, followed by a rapid generation phase, and finally reached the peak concentration at 12 h. The reaction was carried out at a low temperature (0.5 \({}^{\circ}\)C). It is noteworthy that, although the reaction process showed a staged rate change, the overall conformity to the zero-order kinetic model may be related to the continuous supply of precursor substances in the reaction system. For the more structurally complex 2,6-dimethylpyrazine (Figure 2, Table 4), higher activation energy conditions are required for its generation. In the range of 100-110 \({}^{\circ}\)C, the concentration of the compounds remained below the detection limit even after extending the treatment time to 12 h. The concentration of the compounds in the range of 100-110 \({}^{\circ}\)C was lower than the detection limit. When the temperature was raised to 120 \({}^{\circ}\)C, only trace presence was detected for the first 2 h, but the concentration increased significantly after the treatment time exceeded 4 h. The concentration of the compounds in the range of 100-110 \({}^{\circ}\)C was significantly higher than the detection limit. Despite the significant nonlinear characteristics of the generation process, the data could still be well fitted by a zero-level kinetic equation, which is in agreement with the findings of [PERSON] et al. [29] in a cocoa bean roasting system.