SBSE-GC-MS Analysis the Differential Aroma Components of Ning Black Teas at Different Quality Levels

Ning black tea is one of the earliest congou black teas in China. To investigate the aroma components of Ning black teas, different grades (tribute, special grade and first grade) of Ning black teas were collected and sensorily evaluated. Aroma components were analyzed by stirring bar adsorption extraction (SBSE) combined with gas chromatography-mass spectrometry, and the differential aroma components were screened out via statistical analysis. Finally, partial least squares regression analysis (PLS-RA) was used to identify the key differential aroma components that have an important impact on the aroma quality of different grades of Ning black teas. The sensory evaluation result showed that the overall quality of Ning black tea increased with its grade. In total, 142 volatile components were identified, which were divided into 9 categories, mainly consisting of the esters (41.29%) and alcohols (30.03%). Methyl salicylate (217.44‰), linalool (88.52‰), geraniol (65.54‰), β-ionone (56.07‰), phytol (52.72‰), and phenyleacetaldehyde (41.04‰) amongst others were the main aroma components. A total of 69 volatile components showed extremely significant differences (P<0.01). Among them, the relative contents of α-cubebene, linalool, linalool oxides IV, β-myrcene, nerol, neral, and trans-β-ocimene amongst others, which mainly present pleasant sweet, floral, and fruity odors, were higher in the tribute grade of Ning black tea. The relative contents of β-cyclocitral, theaspirane, benzyl caproate and geranyl caproate amongst others were higher in the special grade of Ning black tea, and the relative contents of phytol, benzyl salicylate, trans-2-hexenyl caproate, ethyl decanoate and naphthalene amongst others were higher in the first grade of Ning black tea. PLS-RA further showed that pleasant aroma components such as β-myrcene, allo-ocimene, gleenol, α-cubebene, nerol and neral were significantly and positively correlated with the aroma scores of Ning black tea, while methyl trans-9-octadecenoate, dibenzofuran, neophytadiene, phytol, benzyl salicylate and naphthalene were significantly and negatively correlated with the aroma scores of Ning black tea. The results of this study contribute to elucidate the chemical basis of aroma quality of Ning black teas and provide a theoretical support for improving the aroma quality of Ning black tea in processing practice.