Analysis of Aroma Differences between Hunan Compressed Dark Tea and Raw Dark Tea

To explore the differences in aroma between compressed dark tea and raw dark tea, headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and sensory evaluation were used to analyze and compare the flavor quality and aroma composition of four kinds of Hunan compressed dark tea and raw dark tea stored under the same condition. The results showed that compared with the raw tea, the pine smoke-like aroma and the crude, green, sour and other miscellaneous off-odors of the compressed tea were weaker, the concentration of aroma was higher and more long-lasting, and the stable flavor was more prominent. Furthermore, the contents of 15 unpleasant aroma components such as (E,Z)-2,4-heptadienal, 2,3,5,6-tetramethylpyrazine, and acetic acid in the compressed tea decreased, while the contents of 11 pleasant aroma components such as (E,E)-2,4-heptadienal, saffron aldehyde and butylated hydroxytoluene increased. Through principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA), 10 characteristic aroma components which could potentially be used to discriminate between compressed dark tea and raw dark tea were identified including acetic acid, 2-butyl-1-octanol, 1,2,3-trimethylbenzene, (Z)-2-decylenaldehyde, linalool, octanol, α-terpineol, 3-tridecanone, (E,Z)-2,6-nonadienol and phenylethanol. These results can provide a reference for further research on the quality formation mechanism of Hunan dark tea and the development of dark tea products.