2 research outputs found
Formation of Volatile Tea Constituent Indole During the Oolong Tea Manufacturing Process
Indole is a characteristic
volatile constituent in oolong tea.
Our previous study indicated that indole was mostly accumulated at
the turn over stage of oolong tea manufacturing process. However,
formation of indole in tea leaves remains unknown. In this study,
one tryptophan synthase α-subunit (TSA) and three tryptophan
synthase β-subunits (TSBs) from tea leaves were isolated, cloned,
sequenced, and functionally characterized. Combination of CsTSA and
CsTSB2 recombinant protein produced in <i>Escherichia coli</i> exhibited the ability of transformation from indole-3-glycerol phosphate
to indole. CsTSB2 was highly expressed during the turn over process
of oolong tea. Continuous mechanical damage, simulating the turn over
process, significantly enhanced the expression level of CsTSB2 and
amount of indole. These suggested that accumulation of indole in oolong
tea was due to the activation of CsTSB2 by continuous wounding stress
from the turn over process. Black teas contain much less indole, although
wounding stress is also involved in the manufacturing process. Stable
isotope labeling indicated that tea leaf cell disruption from the
rolling process of black tea did not lead to the conversion of indole,
but terminated the synthesis of indole. Our study provided evidence
concerning formation of indole in tea leaves for the first time
Does Enzymatic Hydrolysis of Glycosidically Bound Volatile Compounds Really Contribute to the Formation of Volatile Compounds During the Oolong Tea Manufacturing Process?
It
was generally thought that aroma of oolong tea resulted from hydrolysis
of glycosidically bound volatiles (GBVs). In this study, most GBVs
showed no reduction during the oolong tea manufacturing process. β-Glycosidases
either at protein or gene level were not activated during the manufacturing
process. Subcellular localization of β-primeverosidase provided
evidence that β-primeverosidase was located in the leaf cell
wall. The cell wall remained intact during the enzyme-active manufacturing
process. After the leaf cell disruption, GBV content was reduced.
These findings reveal that, during the enzyme-active process of oolong
tea, nondisruption of the leaf cell walls resulted in impossibility
of interaction of GBVs and β-glycosidases. Indole, jasmine lactone,
and <i>trans</i>-nerolidol were characteristic volatiles
produced from the manufacturing process. Interestingly, the contents
of the three volatiles was reduced after the leaf cell disruption,
suggesting that mechanical damage with the cell disruption, which
is similar to black tea manufacturing, did not induce accumulation
of the three volatiles. In addition, 11 volatiles with flavor dilution
factor ≥4<sup>4</sup> were identified as relatively potent
odorants in the oolong tea. These results suggest that enzymatic hydrolysis
of GBVs was not involved in the formation of volatiles of oolong tea,
and some characteristic volatiles with potent odorants were produced
from the manufacturing process