【作者】 刘跃云；

【导师】 杨坚； 叶阳；

【作者基本信息】 西南大学 ， 茶学， 2011， 硕士

【摘要】 茶叶含有丰富的有益于人体健康的营养成分和疗效成分,是世界三大无酒精饮料之一,也是中国的国饮和传统的出口商品。随着社会的快速发展,人们生活水平的提高,人们的消费水平也随之提高,这就产生“高档茶畅销、低档茶滞销”的现象。目前,传统名优绿茶生产加工仅限于春季,但春季生产季短,原料有限,难以形成批量生产来满足市场需求。这就要求打破春季绿茶的局限,加大其它季节绿茶的开发力度。相对春茶,夏秋茶生产期长,热量条件丰实,茶树生长快,发展潜力很大。然而,夏秋茶味苦涩,味阀值高,色泽暗沉。夏秋绿茶的品质提升,能较大程度的增加资源利用率,提高茶叶价格,有切实的经济效益。干茶色泽、汤色、叶底色泽在茶叶感官品质八项因子中占三项,一定程度上反映了绿茶品质的好坏。对夏秋绿茶色泽品质的提升,无论是提高整体产品质量,还是促进茶叶销售都非常重要。本试验把真空冷冻干燥技术运用到茶叶加工中。采用夏秋季节成品茶复水后,比较真空冷冻干燥技术、微波干燥技术、烘干技术、远红外干燥技术对茶叶色泽的提升效果,结合感官审评、色差测定以及化学成分分析,探讨真空冷冻干燥提升茶叶色泽的机理。正交试验确定真空冷冻干燥技术在绿茶加工中的最佳参数条件,对真空冷冻干燥之后的后续干燥方式进行选择。以龙井43茶青为原料应用冻干的最佳工艺和最佳后续干燥方式进行叶茶和碎茶的试验。得出以下结论：1、茶样复水后经过真空冷冻干燥、微波干燥、烘干、远红外干燥的比较发现：真空冻干的干茶和叶底-a/b值高于其它样。感官审评中,真空冷冻干燥茶样的外形色泽和叶底色泽优于其它处理,显著优于未处理样。真空冷冻干燥样的审评总分显著高于未处理样。经过处理的茶样水浸出物、游离氨基酸、茶多酚含量减少,酚氨比低于未处理样,处理间差异不显著。真空冻干样的黄酮总量与黄酮苷的含量均显著高于未处理样和其它处理,而叶绿素a,叶绿素b,总叶绿素含量均低于未处理样。真空冻干利于茶样干茶色泽和叶底色泽的提升,总体品质部分提升,滋味品质保持。黄酮总量和黄酮苷组分含量的增加对茶样干茶和叶底色泽改善有一定的作用。推测复水处理使得茶样的黄酮及其苷类物质大部分浸出在茶叶表面,而真空冷冻干燥对这些物质最大限度的保持,避免了高温的破坏。2、冻干参数研究的试验中,茶叶含水量为最主要因素,茶叶含水量对茶样外形色泽,叶底色泽,汤色亮度,汤色绿度,干茶亮度,干茶绿度均有较大影响。冻干时间对干茶亮度和茶汤亮度影响较大,冻干机预冻温度和茶叶复水水温对叶底颜色影响较大。数据显示含水量45%,冻干时间3h,干茶与叶底的-a／b值最好,绿度最高。冻干机预冻温度和茶叶复水水温对试验结果影响不大,分别取预冻到-25℃和复水水温25℃。从冻干的后续干燥试验得知,各处理样的茶汤,干茶的绿度没有明显差异。感官审评汤色,总分以烘干的最好,选择烘干的干燥方式。3、采用龙井43制得的碎茶中,经过微波杀青揉切真空冷冻干燥的茶样外形和汤色得分,叶底的-a/b值显著高于其它,感官审评总分各处理无显著差异。微波杀青揉切真空冷冻干燥利于茶叶色泽的优化,特别是干茶色泽和汤色,以及叶底的绿度得改善。同时,冻干处理对茶叶总体品质不造成影响。4、采用龙井43制得的叶茶中,微波杀青重揉捻烘干后再复水真空冷冻干燥的茶样干茶外形色泽显著优于未复水样,干茶的-a值以及-a/b值显著高于其它,其感官审评总分增加不明显,内含物质与其它处理略有差别,其中咖啡碱增加明显。叶茶微波杀青重揉捻烘干后再复水真空冷冻干燥利于茶叶干茶色泽的保持,其外形色泽和干茶绿度有较大的提升,推测是复水后黄酮类水溶性色素溶解于茶叶表面,真空冷冻干燥使茶叶色素有很好的保持。更多还原

【Abstract】 Rich in nutritious and efficacious ingredients to human health, tea is one of the world’s three non-alcoholic beverageswhich is also China’s national drink and the traditional export commodities. With the rapid development of society and people’s living standards, the phenomenon of "high-grade tea is best seller, low-grade tea is dead stock" appeared. At present traditional famous green tea is often made in the spring, but the production season is short, raw material is difficult to meet market demand. Improving the quality of summer-autumn tea can increase resource utilization and tea prices, which create real economic benefits. To a certain degree, color of dry tea, soup and infused leaf reflect the quality of green tea. With the development of quality of summer-autumn tea, tea sales will become very easy.In this study, the vacuum freeze-drying technology was applied to tea processing. After summer-autumn tea rehydrate, in order to enhance the color of tea, compared vacuum freeze-drying, microwave drying, drying and far infrared drying technology, combined with sensory evaluation, color determination and chemical composition analysis, and investigated vacuum freeze-drying mechanism. The best parameters in green tea processing by vacuum freeze-drying technology were determined by orthogonal experiment. Longjing 43 is fresh tea leaves as raw material, which was used to do the test about tea and broken tea by the application of freeze-drying and the best way of follow-up drying. The conclusions are as follows:1.After tea samples rehydrate, compared vacuum freeze-drying, microwave drying, drying and infrared drying method found that:the-a/b value of dry tea and infused leaf are higher than the other samples by the vacuum freeze-drying. In the sensory evaluation, the color of tea samples by vacuum freeze-drying is better than other and is significantly better than CK, but water extractum and phenol ammonia ratio is lower than CK; The total flavonoids and flavonoid glycosides are higher than CK, and chlorophyll a, chlorophyll b, total chlorophyll content are lower than CK. Vacuum freeze-drying is propitious to color, total flavonoids and flavonoid glycosides enhancement.2.In the lyophilization experiment, the moisture content of tea is most important factors. Drying time have a greater impact on the brightness of dry tea and soup, freeze dryer pre-freezing temperature and water temperature have a greater impact on tea leaves color. The results showed that the optimal conditions is moisture content 45%, drying time 3 h. Freeze dryer pre-freezing temperature and rehydration temperature of tea has little effect on the experimental results.3.The broken tea was made by Longjing 43, which shape and soup color, the-a/b values of infused leaf are better than the other by microwave deactivation of enzymes, rolled and vacuum freeze-drying. The total points have no significant difference by sensory evaluation. Microwave deactivation of enzymes, cut and vacuum freeze-drying are in favor of the color of tea, especially the color of dry tea and soup.4.The shape and color of tea samples that is longjing43 is better than nonrehydration samples by microwave deactivation of enzymes, re-rolled and then vacuum freeze-drying, the -a and -a/b value of dry tea was significantly higher than the other, its sensory evaluation scores have no significant increase. Contains material are slightly different, in which caffeine increases. The color of dry tea can maintain by microwave deactivation of enzymes, re-rolled and then vacuum freeze-drying and then rehydration.更多还原