Monitoring the dynamic changes in aroma during the whole processing of Qingzhuan tea at an industrial scale: From fresh leaves to finished tea.

Aroma is one of the most outstanding quality characteristics of Qingzhuan tea (QZT), but its formation is still unclear. Thus, the volatile organic compounds (VOCs) during the whole processing of QZT were investigated by headspace solid-phase microextraction/gas chromatography-mass spectrometry. Based on 144 identified VOCs, the results showed that de-enzyming, sun-drying, and piling fermentation were the key processes of QZT aroma formation. Furtherly, 42 differential VOCs (VIP > 1.0 and p < 0.05) and 16 key VOCs (rOAV > 1.0 and/or ROAV > 1.0) were screened. Especially, sulcatone and ß-ionone (rOAV > 100 and ROAV > 10) were considered the most important contributors to the aroma of QZT. The metabolisms of key VOCs were mainly involved in oxidative degradation of fatty acids, degradation of carotenoids, and methylation of gallic acid. This study could help to more comprehensively understand the aroma formation in QZT processing at an industrial scale.

Dynamic changes in the aroma profiles and volatiles of Enshi Yulu tea throughout its industrial processing.

Although Enshi Yulu tea (ESYL) possesses a distinctive fragrance, there is a scarcity of studies focusing on its primary volatiles or aroma genesis. This study aims to elucidate the dynamics in the profiles of aromas and volatiles through aroma profiling analysis and headspace solid-phase microextraction/gas chromatography-mass spectrometry. A total of 10 aroma attributes and 128 volatiles were identified in ESYL, with geraniol and linalool exhibiting the highest levels, and alcohols constituting the predominant proportion. Besides, a relative odor activity value (ROAV) based molecular aroma wheel was constructed, revealing 12 key odorants with ROAVs >1, wherein linalool, ß-ionone, and nonanal ranked highest. Notably, steaming and final drying emerged as critical steps for ESYL aroma development, while the non-enzymatic degradation of fatty acids likely contributed to the formation of its fresh aroma. These findings significantly enhance our comprehension of ESYL aroma formation.

Microbial community succession in the fermentation of Qingzhuan tea at various temperatures and their correlations with the quality formation.

With the aim to reveal the microbial community succession at various temperatures in the fermentation of Qingzhuan tea (QZT), the Illumina NovaSeq sequencing was carried out to analyze bacterial and fungal community structure in tea samples collected from the fermentation set at various temperatures, i.e., 25 °C, 30 °C, 37 °C, 45 °C, 55 °C, and room temperature. The results showed that fermentation temperature profoundly affected the microbial community succession in the QZT fermentation. Microbial richness and community diversity decreased along with the increase of fermentation temperature. Despite the differences between microorganisms and their metabolic types among various temperatures, most bacteria and fungi showed positive correlations at the genera level. Klebsiella, Paenibacillus, Cohnella, and Pantoea were confirmed as the main bacterial genera, and Aspergillus and Cyberlindnera were the main fungal genera in QZT fermentation. The microbial genera (i.e. Aspergillus, Rhizomucor, Thermomyces, Ralstonia, Castellaniella, and Vibrio) were positively correlated with fermentation temperature (P < 0.05), while Klebsiella, Paenibacillus, and Aspergillus had good adaptability at different temperatures. Conversely, Pantoea and Cyberlindnera were only suitable for low temperature (≤37 °C) growth, and Thermomyces was only suitable for high temperature (>37 °C) growth. Aspergillus had a significant positive correlation with tea aroma quality (r = 0.64, p < 0.05). This study would help to understand the formation mechanism of QZT from microflora perspective.