86(P81) 茶のアルコール系香気生成の分子機構(ポスター発表の部)

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In the course of our studies on aroma formation mechanism in oolong tea (Camellia sinensis var. sinensis cvs. Shuixian and Maoxie), we have shown in molecular basis that most of alcoholic tea aroma are generated by endogenous enzymatic hydrolysis of glycosidic aroma precursors during tea manufac-turing. We have isolated and identified main alcoholic aroma precursors of geraniol, linalool, 2-phenyl-ethanol, benzyl alcohol, linalool oxides I and II (trans- and cis-linalool 3,6-oxides) and methyl salicylate as β-primeverosides (6-O-β-D-xylopyranosyl-β-D-glucopyranosides), guided by an enzymatic hydroly-sis (with the acetone powder prepared from cv. Yabukita) followed by GC and GC-MS analyses. Aroma precursors of linalool oxides III and IV (trans- and cis-linalool 3,7-oxides) and (Z)-3-hexenol were exceptionally isolated as 6-O-β-D-apiofuranosyl-β-D-glucopyranosides and a β-D-glucopyrano-side, respectively, from the oolong tea leaves. In cv. Yabukita for green tea benzyl alcohol was found to be stored as ca. 1:1 mixture of β-primeveroside and β-D-glucopyranoside. As a preliminary experiment we purified a new glycosidase β-primeverosidase) from fresh leaves of cv. Yabukita by ammonium sulfate precipitation followed by chromatographies with CM-Toyopearl and Mono S-HR. This glycosidase was found to be one of the main glycosidases involved in the alcoholic aroma formation in tea leaves. This is the second example of β-primeverosidases. Purification of the β-primeverosidase from fresh oolong tea leaves (cv. Shuixian) was also carried out in the same manner. The molecular weight was shown to be 61kDa and 60.3kDa by SDS-PAGE and TOFMS, respectively. Its pI and optimum temperature and pH are 9.5, 45℃ and 4,respectively. The enzyme is stable below 45℃, and between pH 3 to 5. These enzymic characteristics are quite similar to those of the β-primeverosidase from cv. Yabukita. The β-primeverosidase was found to hydrolyze a β-apiofuranoside into each constituent dissacharide and aglycon without further hydrolysis as effectively as in the cse of a β-primeveroside. Amounts of alcoholic aroma precursor and glycosidase activity in each part of the tea shoot (cvs. Yabukita and Izumi) were indirectly measured by means of a crude enzyme assay. The aroma precursors were abundant in young leaves and decreased as the leaf aged. Glycosidase activity also decreased as leaves aged, but was high in stems.
天然有機化合物討論会の論文
1996-09-02

86(P81) 茶のアルコール系香気生成の分子機構(ポスター発表の部)

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