Comparison of Different Grades of Innovative Tanyang Congou Black Tea (Minkehong) Based on Metabolomics and Sensory Evaluation

Innovative Tangyang Congou black tea, also known as Minkehong black tea (MKH), is of high quality and hence has gained a reputation on the market. In this study, standard samples of MKH were used as the research material, and the results of sensory evaluation showed that the overall quality of MKH decreased along with the downgrading. The radar chart showed a strong association between higher grades and specific aroma and taste character. Based on the detection of ultra-performance liquid chromatography–mass spectrometry (UPLC–MS) and related analysis, the content of both the ester-type catechins and non-ester catechins decreased along with the downgrading, and the details of their change trends were revealed. The content and dynamic changes in caffeine were also investigated. A total of 19 kinds of amino acids (AAs) were clustered; among them, 4 kinds of AAs, namely, Thr, Leu, Asp, and Ile, significantly contributed to the taste of the tea. Notably, the content of Thr had the highest correlation with the grade of MKH, and the correlation coefficient was 0.991 (p < 0.01). According to gas chromatography–mass spectrometry (GC–MS) detection and analysis, a total of 861 kinds of volatile compounds were detected, the aroma-active compounds in different grades were selected, and an aroma wheel of MKH was constructed. Our results found that non-volatile and volatile compounds not only contribute to defining the level of MKH standard samples but also provide a chemical basis for the measurement of flavour and quality of MKH.