Formation of terpenoids contributing to tea aroma.

萜烯醇是茶叶香气的主要成分，是茶叶加工过程中形成的。研究了茶叶中香气物质前体物的测定及酶促反应生成醇类物质的方法。1)香叶基-D-葡萄糖苷被认为是香叶醇形成的前体之一。合成了该糖苷，并通过化学分析和光谱分析确定了其结构。2）为了利用粗茶酶系，制备了茶叶丙酮粉。用对硝基苯酚法测定了粉末中β-葡萄糖苷酶的活性，其活性为0.8u/g。3）为了证明香气前体的存在，制备了绿色茶的热水提取物，通过减压下的水蒸气蒸馏和溶剂萃取从其中除去挥发性香气化合物。新形成的香气成分采用气相色谱和气相色谱-质谱联用技术进行分离鉴定。在预期的萜醇类化合物芳樟醇、氧化芳樟醇、香叶醇的基础上，鉴定出苯甲醇和苯乙醇，它们是茶叶香气的主要成分。以上结果表明，茶叶香气成分主要是通过酶促反应形成的前体物质。5）合成的香叶醇- -D-葡萄糖苷也在上述条件下用茶叶丙酮粉水解。产物显示为香叶醇与其异构体橙花醇的2：1混合物。由GC峰面积推算出萜醇的得率为10.6%。

Terpene alcohols are main components in tea aroma, which are formed during tea processing. The estimation for the aroma compound precursor in tea leaf and the formation of the alcohols by enzymatic reaction are investigated. 1) Geranyl- -D-glucoside has been supposed to be one of the precursor of geraniol formation. This glycoside was synthesized and its structure was established from chemical and spectrometric analyses.2) In order to use a crude tea enzyme system, the aceton powder of tea leaf were prepared. The -glucosidase activity in the powder was measured by p-nitrophenol method and its activity was 0.8u/g.3) To certify the presence of aroma precursor, hot water extract of green tea was prepared, from which volatile aroma compounds were taken off by steam distillation under the reduced pressure and by the solvent extraction.4) The water extract was treated with tea leaf aceton powder in sodium citrate buffer solution. The newly formed aroma volatiles are separated and identified by GC and GC-MS equipped with capillary column. With the expecting terpene alcohols such as linalool, linalool oxide and geraniol, benzyl alcohol and phenylethyl alcohol are identified, which are known as main component of tea aroma. These results suggest that all main components in tea aroma are formed their precursors by enzymatic reaction.5) The synthesized geraniol- -D-glucoside was also hydrolysed by tea leaf aceton powder under the same condition described above. The product was shown to be 2:1 mixture of geraniol and its isomer, nerol. The yield of terpene alcohols from the glucoside was culculated to be 10.6% from their peak area on GC.