Dynamics Change of Metabolites during the Manufacturing Process of Wuyi Rougui Tea (Camellia sinensis cv. Rougui) Revealed by Widely Targeted Metabolomics Analysis

In this study, widely targeted metabolomics analysis was used to investigate the dynamic changes of total metabolites of Wuyi Rougui tea during the manufacturing process. The results showed that a total of 783 volatile metabolites and 975 non-volatile metabolites were detected in fresh tea leaves and five manufacturing stages (withering, shaking, fixation, rolling, and drying). After fresh tea leaves were manufactured into primary tea, the content of total volatile metabolites decreased by 70.7% while the content of total non-volatile metabolites increased by 27.8%. During the manufacturing process, the content of total volatile metabolites firstly increased and then decreased, reaching its peak at the shaking stage. The content of total non-volatile substances increased significantly at the withering and shaking (by 24.3%) steps. The results of principal component analysis (PCA) and cluster analysis (CA) showed that the differences in the total metabolites between fresh tea leaves and the withering stage were less than those among the other stages. All the samples at different manufacturing stages could be clearly distinguished. Orthogonal partial least squares-discriminant analysis (OPLS-DA) identified 556 characteristic compounds, including flavones (alcohols) glycosides, quinic acid, L-aspartic acid, theobromine, palmitic acid, 2-hexanoylfuran, β-ocimene, 3-(4-methyl-3-pentenyl)-furan, (E)-butanoic acid, 3-hexenyl ester, and 2,6,6-trimethylbicyclo[3.2.0]hept-2-en-7-one as differential metabolites to distinguish tea samples at different manufacturing stages. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that free amino acids were significantly enriched at the withering and shaking stages, flavonoids at the drying stage, terpenoids and free fatty at all manufacturing stages, alcohol, ester, ketone and aldehyde compounds at the fixation, rolling, and drying stages. This study provides a theoretical basis for further improving the quality of Wuyi Rougui tea.