Analysis of aroma precursors in Jinmudan fresh tea leaves and dynamic change of fatty acid volatile during black tea processing
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ABSTRACT:
SUBMITTER: Qingyang W
PROVIDER: S-EPMC10869310 | biostudies-literature | 2024 Feb
REPOSITORIES: biostudies-literature
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Project description:The application of shaking during the withering process has been shown to significantly enhance the floral aroma of black tea. However, prior to this study, there was limited research on the effects of shaking combined with other withering treatments on the aroma components of black tea. In this study, the aroma attributes of black teas processed with shaking combinations of yellow-light or high-temperature withering (YLS, HTS, and HYS) were evaluated through sensory evaluation, and the volatile composition and identification of key aroma compounds in black teas and in-process withered tea leaves were analyzed by gas chromatography-mass spectrometry (GC-MS). The results indicated that black teas subjected to different shaking combinations exhibited a distinct floral aroma with higher volatile compound content, with the YLS treatment showing the most significant aroma improvement. Eight volatile compounds with relative odor activity values (rOAV) > 1 were identified from 53 differential volatile compounds in black tea under different shaking combinations as the most important contributors to aroma quality. Linalool, trans-β-Ionone, α-cedrene, and nonanal were identified as key floral volatiles with high rOAVs. Their concentrations in YLS were notably higher compared to those in S, both in withered tea leaves (with the exception of trans-β-Ionone) and in the final dry black teas, suggesting that there may be a synergistic effect between the yellow-light withering and the shaking process in enhancing these key floral compounds. Overall, this study found that shaking combined with yellow-light withering can improve the aroma composition and quality of black tea, providing a theoretical basis and practical guidance for the production and optimization of high-aroma black tea.
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Project description:Shaking is an innovative technology employed in black tea processing to enhance flavor. However, the effects of shaking on the evolutionary mechanisms of volatile metabolites (VMs) remain unclear. In this study, we compared the effects of a shaking-withering method with those of traditional withering on the flavor and VMs transformation of black tea. The results showed that black tea treated with shaking exhibited excellent quality with floral and fruity aroma. Based on gas chromatography-tandem mass spectrometry, 128 VMs (eight categories) were detected. Combining variable importance projection with odor activity value analysis, eight key differential VMs were identified. Shaking could promote the oxidative degradation of fatty acids and carotenoids and modulate the biosynthesis of terpenoids to facilitate the formation of floral/fruity VMs (such as (Z)-hexanoic acid-3-hexenyl ester, ethyl hexanoate, trans-β-ionone, and decanal). Our findings provide theoretical guidance for the production of high-quality black tea with floral and fruity aromas.
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Project description:Flat black tea (FBT) has been innovatively developed to alleviate homogenisation competition, but the dynamic changes in aroma components during the process remain unclear. This study employed HS-SPME-GC-MS to analyse the aroma components of tea samples from various processing stages of FBT, and to make a comparative assessment with conventional strip-like Congou black tea (SBT). Additionally, a proteomic analysis was conducted on fresh leaves, withered leaves, and frozen-thawed leaves. Significant changes were observed in the aroma components and proteins during the processing. The results of the multivariate and odour activity value analysis demonstrated that the principal aroma components present during the processing of FBT were linalool, (E)-2-hexen-1-al, methyl salicylate, geraniol, hexanal, benzeneacetaldehyde, (Z)-3-hexenyl butyrate, dimethyl sulphide, 2-methylbutanal, 2-ethylfuran, nonanal, nonanol, 3-methylbutanal, (Z)-3-hexen-1-ol, 2-pentylfuran, linalool oxide I, and β-myrcene. Freezing-thawing and final roasting are the key processing steps for forming the aroma quality of FBT. The final roasting yielded a considerable quantity of pyrazines and pyrroles, resulting in a high-fried aroma, but caused a significant reduction in linalool, geraniol, β-myrcene, and esters, which led to a loss of floral and fruity aromas. The freezing-thawing treatment resulted in an accelerated loss of aroma substances, accompanied by a decrease in the expression level of lipoxygenase and 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase. The formation of aroma substances in the linoleic acid metabolic pathway and terpenoid metabolic process was hindered, which had a negative impact on tea aroma. This study elucidates the causes of unsatisfactory aroma quality in tea products made from frozen tea leaves, providing theoretical support for the utilisation of frostbitten tea leaves, and helps us to understand the mechanism of aroma formation in black tea.
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Project description:1. A marked decrease in the total RNA content during the withering process of tea leaves was found. During the fermentation process, there was a small but significant decrease in the total RNA content. 2. During isolation of RNA from tea leaf tissues, the action of leaf ribonuclease was minimized by the addition of sodium dodecyl sulphate during extraction; 1% (w/v) sodium dodecyl sulphate in 0.2m-tris-hydrochloric acid buffer, pH8.0, containing 0.005% EDTA was found to be most efficient for the extraction and gave about 93% yield. 3. The total RNA preparations isolated from fresh, withered and fermented tea leaves were compared with regard to nucleotide composition and spectral characteristics. The total RNA preparations from all three sources contained more purines than pyrimidines (purine/pyrimidine ratio 1.47-1.52).
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Project description:Panning is a processing step used in manufacturing of some varieties of oolong tea. There is limited information available on effects of panning on oolong tea flavors. The goal of this study was to determine effects of panning on flavor volatile compositions of oolong using Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-Olfactometry (GC-O). SDE and SPME techniques were applied for extraction of volatiles in panned and unpanned teas. A total of 190 volatiles were identified from SDE and SPME extractions using GC-MS and GC-O. There were no significant differences (P > 0.05) in aldehyde or terpene contents of unpanned and panned tea. However, alcohols, ketones, acids and esters contents were significantly reduced by panning. Among 12 major volatiles previously used for identification and quality assessment of oolong tea, trans nerolidol, 2- hexenal, benzaldehyde, indole, gernaiol, and benzenacetaldehyde contents were significantly decreased (P < 0.05) by panning. Panning increased (P < 0.05) contents of linalool oxide, cis jasmone, and methyl salicylate. The GC-O study also showed an increase of aroma active compounds with sweet descriptions and decrease of aroma active compounds with fruity and smoky descriptions after panning. Panning significantly changes the volatile compositions of the tea and created new aroma active compounds. Results from this study can be used in quality assessment of panned oolong tea.
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Project description:In this study, a unique tea cultivar ‘Anxi kucha’ was discovered for the first time, which is rich in both secondary metabolites. In the targeted data, theacrine (17.44 mg/g) was detected only in the ‘Anxi kucha’ tea plant in the test materials. The content of EGCG3"Me in ‘Anxi kucha’ (11.25mg/g), ‘Tieguanyin’ (5.32mg/g) and ‘Fudingdabaicha’ (0.93mg/g) showed high, medium and low changes. Through proteomics and transcriptomics, it was identified that the key pathways for the synthesis of theacrine and EGCG3"Me were the purine metabolism pathway and the flavonoid biosynthesis pathway, respectively. Combined proteome-transcriptome-metabolome analysis showed that SAMS3, APRT1, IMPDH, and TCS1 were the main enzymes promoting theacrine synthesis; CHI1, CHI2, FLS2 and LAR1 were the main enzymes that promote the synthesis of EGCG3"Me. The results of transcription factor analysis showed that MYB4 and bHLH74 had positive regulatory effects on the synthesis of theacrine and EGCG3"Me. Theacrine and EGCG3"Me are both bitter compounds. This study provides a valuable material rich in theacrine and EGCG3"Me, which provides a material basis for further development and utilization in the field of tea health food and a theoretical basis for studying the functional components of tea.
2025-05-26 | PXD062468 | Pride