Generalized model of catechins and microstructure study in the withering process of green tea

This study aims to explore the variation patterns of catechin content under different green tea withering process conditions and to develop a generalized model. The influencing factors considered include initial moisture content (A), withering hot air temperature (B), withering hot air humidity (C), and withering hot air velocity (D). Employing Design-Expert software, an orthogonal experimental design was conducted to investigate the effects of these factors and their interactions on catechin content in tea. Additionally, scanning electron microscopy was used to observe the microstructure of the withered leaves. The response surface analysis revealed model significance (R²=0.9072), indicating that the quality model for catechins concerning the four influencing factors is highly significant, with a non-significant lack of fit, confirming the model’s statistical validity. The interaction between withering hot air temperature (B) and velocity (D) had the most significant impact on catechin content, likely due to changes in catechin oxidase activity in fresh tea leaves within specific temperature and velocity ranges, which in turn affected catechin production. When A, B, C, and D were set at 84.61%, 25.27 °C, 65.62%, and 0.14 m/s respectively, the catechin content (mass fraction) reached an optimal value of 40.62%. The generalized model derived is: Catechin content = + 12.74 + 2.68 A − 1.70 B − 0.65 C − 2.71 D − 1.37AB + 1.38AC − 0.20AD − 1.11BC + 6.08BD − 1.35CD − 1.28 A² − 1.54 B² − 0.52 C² − 1.08 D². This model provides a theoretical basis for advancing key technologies in the development of green tea withering processes and equipment.