Metabolic Accumulation of Tea Theaflavins, Thearubicin, and Theabrownin Quality-Related Molecules by Surface-Enhanced Raman Spectroscopy (SERS)

The development of a rapid and simple method for the determination of theaflavins, thearubicin, and theabrownin quality-related molecules is very beneficial for the study of the fermentation process of black tea. This chapter takes the fermentation process of black tea as an example. Surface-enhanced Raman spectroscopy (SERS) and chemometrics method are used to detect theaflavins, thearubicin, and theabrownin quality-related molecules. The results show that this method can be used to determine the optimal fermentation stage of black tea. The important Raman peaks at 317.71, 619.59, 731.48, 956.08, and 1326.70 cm−1 were found for monitoring quality changes of black tea by density functional analysis and correlation analysis. The prediction r2 for catechin (C) and epigallocatechin gallate (EGCG) reached 0.81 and 0.82, respectively, by integrated SERS with a one-dimensional convolutional neural network (1D-CNN). In conclusion, this chapter revealed the Raman fingerprint characteristics of key compounds associated with the fermentation quality of black tea, presenting an opportunity to quantify the quality changes of tea during fermentation using SERS data. With the monitoring method developed in this research, the optimal fermentation stage can be determined accurately, thus decreasing fermentation costs and improving tea quality.