Analysis of Tea Quality of Large-Leaf Black Tea with Different Harvesting Tenderness Based on Metabolomics

The harvesting tenderness of tea fresh leaves has a significant effect on the flavor and aroma quality of black tea (BT), which is one of the important standards for BT grading. In this study, sensory evaluation, electronic tongue technique and metabolomics were performed to evaluate the flavor and aroma qualities of three different tenderness of large-leaf BTs that were manufactured from the fresh leaves of single-bud, one-bud and one-bud two-leaf teas, respectively. The results of the electronic tongue and sensory evaluation indicated that the increase in the tenderness of the fresh leaf material enhanced the sweetness, freshness and fruity flavor of the tea and reduced the bitterness of the tea. A total of 519 differential flavor components and 84 differential aroma components were identified by metabolomics. Among them, elevated levels of maltitol, cyclic leucine and l-methionine and l-aspartic acid led to elevated sweetness and freshness in more tender tea leaves. Reduced levels of 4-aminosalicylic acid, tyrosol, uracil, inosine, benzamide, and l-tyrosine led to reduced bitterness in BT. Moreover, the content of volatiles such as (Z)-2-Decenal, Phenylacetic acid propyl ester, Acetophenone, and 2-phenylethyl ester were increased, which contributed to the fruity aroma in the high-tenderness tea. This study provides a theoretical basis for grading the flavor quality of BT with different tenderness.