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The 3rd international Conference on O-CILA{Tea)
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ulture and Science
Pr-P-105
EFFECTS OF UV-B ON AROMA FORMATION IN TEA
Q. Ye, G.H. Zhang, J. L. Lu, Y. Y. Du, J.B. Ye, 1. J. Dong, Y. R. Liang*
Zhejiang University Tea Research Institute, 268 Kaixuan Road, Hangzhou 310029, China.
* Correspondent, Tel:+8657186971704, Fax:+8657186971704, E-mail: [email protected]
Summary
Tea aroma is an important factor determining tea quality. Effects ofUV-B on level
of volatiles and expression of genes relating to release of volatiles were investigated.
Expressions of ~-glucosidase and ~-primeverosidase genes were enhanced when fresh
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tea shoots were illuminated by 50 ~W cm- UV-B for 5min. Concentrations of
linaloxide I, a-Terpineol, cis-linaloloxide, 1,6-octadien-3-01, 3,7-dimethyl, phenylethyl
alcohol, benzyl alcohol and phytol were increased after UV-B treatment for 10 min.
Aromatic aldehydes increased at 5 min UV-B treatment. The study showed that short
treatment of UV-B is a good method for improving tea aroma during tea processing.
Keywords
Tea aroma, gene expression,
~-glucosidase, ~-primeverosidase,quality
Introduction
It is known that aromatic compounds in tea are mainly present as glycosides in fresh
tea leaves and are released by endogenous glycosidases during tea manufacturing
process. Many aromatic glycosidic precursors have been isolated from tea plant and
most of them were p-primeverosides. Some of tea aroma precursors were isolated as
~-D- glucopyranside and acuminoside.
~-primeverosidase (TBP)
and p-glucosidase (TBG) are two important glycosidases,
which hydrolyze aroma precursors to liberate volatiles. There were a few reports on
TBP and TBG genes expression in tea. Ultraviolet B (UV-B) is an irradiation with
wavelength 280-320 nm. There have been reports on effects of UV-B on accumulation
of secondary metabolic products such as carotenoid, glycyrrhizin and flavonoids, but
no report about effects ofUV-B on tea aroma formation.
Transient UV-B treatment was used to investigate the effects ofUV-B on formation
of tea volatiles and expression of TBG and TBP genes in tea leaf.
Materials and Methods
Tea shoots with two leaves and a bud were harvested from bushes of Camellia
sinensis cv Maoxie and Anhui-l and ilTadiated using UV-B (50 ~W/cm2) for 0 -20 min.
The treated leaves were fixed in a steamer for 40 s and then dried at 80 °C for 24 h.
Volatiles were extracted by simultaneous distillation and extraction (SDE) and
analyzed by gas chromatography-mass spectrometry (GC-MS).
To investigate the effect of UV-B on gene expression, tea plantlets regenerated from
leaf discs of cultivar Anhui-l were irradiated by UV-B as above method. Leaves were
sampled and frozen in liquid nitrogen and then stored at -70°C until RNA extraction.
Expression profiles of TBG and TBP genes were analyzed by reverse transcriptase
polymerase chain reaction method (II.
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Results and Discussion
Effect of UV-B on formation of tea volatiles
GC-MC revealed that alcoholic volatiles were abundant volatiles but response of
aromatic aldehydes to UV-B was more quickly than alcoholic volatiles. The abundant
alcoholic volatiles were linaloxide I, u-Terpineol, cis-linaloloxide, 1,6-octadien-3-01
and 3,7-dimethyl. Levels of these volatiles increased after UV-B treatment for 10 min
and then decreased. The same tendency was also found in other alcoholic volatiles
such as phenylethyl alcohol, benzyl alcohol and phytol. Major aromatic aldehydes
were benzene acetaldehyde, benzaldehyde and furfural and they were increased at 5
min of UV-B treatment. Some aromatic ketones and esters in tea volatiles including
bis (2-ethylhexyl) phthalate, dibutyl phthalate, 9,12-octadecadienoic acid (z,z)-methyl
ester and acetophenone were also elevated by UV-B treatment.
Expression profiles of TBG and TBP genes
Expressions of TBG and TBP genes were promoted by UV-B treatment and the
highest expression of the two genes were observed at 5 min of UV-B treatment and
then decreased, especially for TBG.
Many studies confirmed that enhanced UV-B radiation exerted an influence on
physiological and biochemical process of plants and plants were injured by excessive
dosage of UV-B, during which expression of genes relating to plant self protections
was accelerated, resulting in accumulation of sun-screen compounds. Cho et al (2007)
found that many up-regulated transcripts were found to encode various proteins
homologous to stress response proteins. The turn-over manipulation and infestation by
tea green leafhopper during manufacture of oolong tea are unique processes that utilize
plant defense responses to elevate the production of volatile compounds. The increase
in expression of TBG and TBP genes and accumulation of volatiles might be a stress
response of tea shoots to UV-B radiation. During traditional processing of oolong tea,
the leaves are illuminated under sunshine for decades of minutes to elevate tea aroma
and UV-B may play important role in the process because UV-B radiation is included
in the sunshine. The significance of the present study is that the indoor UV-B treatment
may replace the outdoor sunshine illumination. The UV-B treatment is not dependent
on the weather and can be carried out anytime.
Acknowledgement
This study was financed by "Key Technology R&D Program" (Project No.
2006BAD06BO1) of the Ministry of Science and Technology of China.
Reference
[1] Mamati GE, Liang YR, Lu JL. Expression of basic genes involved in tea
polyphenol synthesis in relation to accumulation of catechins and total tea
polyphenols. Journal of the Science of Food and Agriculture, 2006,86: 459-464.