Aroma Quality Of Tea Research Articles

Volatile Glycosylation in Tea Plants: Sequential Glycosylations for the Biosynthesis of Aroma β-Primeverosides Are Catalyzed by Two Camellia sinensis Glycosyltransferases.

Tea plants (Camellia sinensis) store volatile organic compounds (VOCs; monoterpene, aromatic, and aliphatic alcohols) in the leaves in the form of water-soluble diglycosides, primarily as β-primeverosides (6-O-β-D-xylopyranosyl-β-D-glucopyranosides). These VOCs play a critical role in plant defenses and tea aroma quality, yet little is known about their biosynthesis and physiological roles in planta. Here, we identified two UDP-glycosyltransferases (UGTs) from C. sinensis, UGT85K11 (CsGT1) and UGT94P1 (CsGT2), converting VOCs into β-primeverosides by sequential glucosylation and xylosylation, respectively. CsGT1 exhibits a broad substrate specificity toward monoterpene, aromatic, and aliphatic alcohols to produce the respective glucosides. On the other hand, CsGT2 specifically catalyzes the xylosylation of the 6'-hydroxy group of the sugar moiety of geranyl β-D-glucopyranoside, producing geranyl β-primeveroside. Homology modeling, followed by site-directed mutagenesis of CsGT2, identified a unique isoleucine-141 residue playing a crucial role in sugar donor specificity toward UDP-xylose. The transcripts of both CsGTs were mainly expressed in young leaves, along with β-primeverosidase encoding a diglycoside-specific glycosidase. In conclusion, our findings reveal the mechanism of aroma β-primeveroside biosynthesis in C. sinensis. This information can be used to preserve tea aroma better during the manufacturing process and to investigate the mechanism of plant chemical defenses.

Development of regression model to differentiate quality of black tea (Dianhong): correlate aroma properties with instrumental data using multiple linear regression analysis

SummaryTo develop a flexible and objective method to discriminate Dianhong tea quality level, the instrumental analysis of odour‐active compounds of three commercial grades of Dianhong tea and quantitative descriptive analysis of their overall aromas were conducted. Eight aroma properties were then statistically correlated with odorants using stepwise multiple linear regression analysis. Thirty‐nine odour‐active components were screened in Dianhong tea infusion, among which dimethyl disulphide and 1‐(1H‐pyrrol‐2yl)‐ethanone were identified for the first time. Adjusted R2 of multiple regression models for eight sensory properties were all >0.95, except ‘resinous’ attribute (R2 = 0.834), and RMSE were <0.18 for all. Regression models showed that 2‐methylbutanal, 3‐methylbutanal, linalool, geraniol, linalool oxides, phenyl acetaldehyde, methyl salicylate, ethyl 2‐methylbutyrate, 3,7‐dimethyl‐3‐octanol, benzaldehyde and 6,10‐dimethyl‐5,9‐undecadien‐2‐one positively contributed to the Dianhong tea aroma profile, while 1‐penten‐3‐ol, (Z)‐3‐hexen‐1‐ol and (E,E)‐2,4‐heptadienal were negative aroma contributors. Regression model development for Dianhong tea aroma quality would provide a uniform standard for objectively assessing tea quality among different laboratories and cultures.

The effect of packaging conditions and storage time on the volatile composition of Assam black tea leaf

Black tea leaf, vacuum packed in Assam and subsequently repacked in the UK in standard air packs, under vacuum or nitrogen- xushed, was stored for up to 48 weeks. The volatile composition of the tea was assessed at zero time, after 16 weeks and 48 weeks. Six compounds were identi wed as signi wcantly di verent at 16 and 48 weeks when compared with the zero time sample ( p < 0.001). These were identi wed as hexanal, trans-2-octenal, trans, cis-2, 4-heptadienal, trans, trans-2, 4-heptadienal, β-cyclocitral and β-ionone, the level of these being at an increased level in the standard air pack and similar to the zero time sample in the vacuumdash and nitrogen- xushed packs. These results are consistent with oxidative deterioration of the tea during storage. Subsequent canonical variate analysis was carried out using these six volatiles. Results indicated clear discrimination between the samples, in particular between the standard air packs and the other samples. This o vers the potential of using these compounds as indicators of tea aroma quality and as a means of distinguishing between tea samples based on exposure time in air.