Chapter 33
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β-Primeverosidase Relationship with Floral Tea Aroma Formation during Processing of Oolong Tea and Black Tea Kanzo Sakata Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Flavor is one the most important factors to determine the quality of beverages. Tea aroma, especially floral aroma liberated from brewed oolong tea and black tea, is so attractive. This study covers the molecular basis of the floral aroma formation during the tea processing. Previous work demonstrated the tea aroma precursors of geraniol, linalool, etc. as β-primeverosides (6-Ο-β-D-xylopyranosyl-β-D-glucopyranosides) from the tea leaves (Camellia sinensis var. sinensis cvs. Shuixian and Maoxie) which can be processed to oolong tea. We have also purified β-primeverosidases from fresh leaves of cv. Yabukita for Japanese green tea, cv. Shuixian for oolong tea and a cultivar of C. s. var. assamica for black tea. The molecular weight of each enzyme was shown to be 60,500, 60,200 and 60,300 by T O F M S , respectively. The enzymatic characteristics (optimum temperature, 45 °C; stable temp., 40-45 °C; optimum p H , 4; pH stability, p H 3-5; specific activity, 0.90-0.99 unit/mg) were very similar to each other. The enzyme was confirmed to effectively hydrolyze the aroma precursors, βprimeverosides as well as 6-O-β-D-apiofuranosyl-β-D -glucopyranoside, into disaccharides and each aglycon without further hydrolysis. Most of the alcoholic tea aroma, which contribute to the floral tea aroma, are primarily stored as disaccharide glycosides (β-primeverosides and 6-O-β-D-apiofuranosyl-β-D-glucopyranosides) and generated by the action of a specific enzyme, β-primeverosidase, during the fermentation process of tea manufacturing.
2000 American Chemical Society
In Caffeinated Beverages; Parliment, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
328
Introduction Any tea leaves can be processed to yield green tea, oolong tea or black tea (Figure 1), although suitable cultivars for each made tea have been developed. Floral
Withering- ^JTurn_j Fixing H .Mass , •Drying-* ^ Oolong tea rolling" over (Semifermented tea) (solar & (rotation (160'C) (10 min, (80-100Ό) indoor) in a basket) χ 5-6)
Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: January 15, 2000 | doi: 10.1021/bk-2000-0754.ch033
1
Fresh tea leaves (Camellia sinensis)
•
Fixing (steaming or parching)
Withering (indoor)
Rolling
Drying
Green tea (Nonfermented tea)
Fermentation (rolling and/or cutting)
Drying
Black tea (Fermented tea)
Figure L Tea manufacturing process.
tea aroma is known to be generated during the fermentation process in the tea manufacturing (Withering and Turn over processes in oolong tea production and Withering and Fermentation processes in black tea production; Figure 1). The process used is one of the most important factors to determine the quality of each made tea, especially oolong tea and black tea (/). Takeo et al. subjected the fresh leaves of cv. Benihomare to the processing for three types of tea (two types of green tea and oolong tea) and compared the G C analytical results among them (Figure 2) (2). It is evident that larger quantities of alcohols such as geraniol are generated during the processing for oolong tea. It was a goal to study the molecular basis of the alcoholic aroma formation in oolong tea. Initially we isolated the aroma precursors of the floral alcohols of tea aroma, and found that most of them were β-primeverosides (ό-Ο-β-D-xylopyranosylβ-D-glucopyranosides (3-7). The aroma precursors of linalool oxides III and IV (cisand fr*
