红、绿茶干燥过程的热化学变化

高温干燥(平均叶温65—70℃)、低温干燥(平均叶温55—60℃)与冷冻干燥比较,加热干燥会使茶叶中的内含成分发生一系列的热化学变化,且以温度高的变化大。在加热干燥中,叶绿素受到破坏,红茶的破坏率大于绿茶,尤其是叶绿素 b 的破坏率较大;红茶中的茶黄素,茶红素下降,茶褐素增加;绿茶中复杂儿茶素有所减少,(-)-EC、(±)-C 有所增加,红茶中的儿茶素减少30%以上,高温处理的下降幅度较小;红茶中的氨基酸下降了9—15%,尤其是茶氨酸、苏氨酸、赖氨酸、丝氨酸、谷氨酸和天门冬氨酸下降较多,高温处理的尤甚;气

Thermochemical Changes of Black Tea and Green Tea during Drying

It is revealed that heating during drying stage is responsible for a seriesof thermochemical changes by comparing heat-drying(leaf temperature:65—70℃ and 55—60℃)with lyophilization,during heat-drying,the rate of dama-ged chlorophyl,especially chlorophyl b,is greater in black tea than that ingreen tea.The contents of theaflavin and thearubigin in black tea decrease,but the content of theabrown increases.The complex catechins decrease but(-)-EC and(-)-C increase to some extent in green tea.The content ofcatechins in black tea is reduced more than 30%,and the content of aminoacids is reduced 9—15%,especially theanine,threonine,lysine,serine,gluta-mic acid and aspartic acid in higher temperature treatment.Gas chromatog-raphic analysis demonstrates that some new aroma components with highboiling point are formed in heat-drying treatments.The ~(14)C tracer experimentshowes that glucose and glutamic acid can be converted into flavour compon-ents during processing.More conversion can be seen in higher temperaturetreatment.Therefore,heat-drying contributes to the quality of green tea andblack tea.