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。研究了茶叶中香气化合物前体的测定及酶促反应生成醇类的方法。1)香叶醇- - d -葡萄糖苷一直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)为了使用粗茶酶体系，制备了茶叶的丙酮粉。采用对硝基酚法测定-葡萄糖苷酶活性，其活性为0.8u/g。3)为了证实香气前驱体的存在，制备了绿茶热水提取物，通过减压蒸汽蒸馏法和溶剂萃取法去除挥发性香气化合物。4)用茶叶丙酮粉在柠檬酸钠缓冲液中处理水提物。采用气相色谱和气相色谱-质谱联用毛细管柱对新形成的香气挥发物进行分离鉴定。通过对芳樟醇、氧化芳樟醇和香叶醇等萜类醇的研究，鉴定出了苯醇和苯乙醇，它们是茶叶香气的主要成分。这些结果表明，茶叶香气的所有主要成分都是通过酶促反应形成的前体。5)合成的香叶醇- d -葡萄糖苷也在相同条件下用茶叶丙酮粉水解。结果表明，该产品是香叶醇和其异构体橙醇的2:1混合物。经气相色谱测定，该葡萄糖苷的萜烯醇收率为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.