Quality of Yashixiang Dancong Tea Affected by Altered Processing Conditions

Objective Effects of a pre-programmed process on the sensory quality of Yashixiang Dancong tea were compared with the traditional tea making procedures to analyze the underline mechanism that caused the differences for technology and quality improvements.

Method A specially designed process (T) was applied to produce Yashixiang Dancong tea in comparison with the traditional tea making (CK). The experimental T withered the leaves lightly followed by constant-speed shaking, and then, fixing for 15 min. In contrast, the conventional process calls for heavy withering, progressive manual shaking, and 10-min fixation. During processing, tea leaves were sampled at the beginning, after withering, in the mid of shaking, at the end of shaking, after fixation, and after completion of drying. Aromatics, free amino acids, catechins, and alkaloids in the sampled leaves were determined using the stir bar sorptive extraction/gas chromatography-mass spectrometry (SBSE/GC–MS) with the changes in catechins and alkaloids analyzed. Sensory attributes of the processed and brewed teas were evaluated by a taste panel with color of the steeped tea measured by a colorimeter.

Result The overall sensory evaluation score of the tea produced by CK was 87.70±1.97, which was significantly higher than that made from T at 84.40±1.07 (P＜0.05). The brewed tea of T was clearer than that of CK with an enhanced green but weakened yellow tone showing a total color difference ΔE* of 19.08±2.29, which was significantly higher than that of CK at 15.86±1.29 (P＜0.05). Collectively, they reflected a lighter fermentation rendered by T than CK. Aromatically, CK was more conducive than T to the formation of the chemicals connotating the typical floral and fruity aroma, such as methyl jasmonate, linalool, geraniol, phenylacetaldehyde, and indole. On the substances related to the taste of tea, T tended to generate higher levels of epigallocatechin gallate at 58.72±2.07mg·g⁻¹ with some methylated catechins and lower contents of umami amino acids, such as glutamic acid and aspartic acid, than CK. Insufficient catechin oxidation and transformation appeared to result in stronger astringency of the tea processed under T than CK. Proper withering and shaking in tea processing seemed to promote the generation of functional polyphenols.

Conclusion The pre-programmed process of T illustrated the significant effects of reduced withering and shaking in limiting polyphenol oxidation and aroma precursor transformation in the Yashixiang Dancong tea making. The insufficient fermentation provided by the process weakened the floral aroma formation and yielded an imbalanced profile on the taste of the tea. Consequently, an optimized withering and shaking would significantly improve Dancong tea quality as well as processing control and efficiency.