【作者】 戴前颖；

【导师】 夏涛；

【作者基本信息】 安徽农业大学 ， 茶学， 2007， 博士

【摘要】 绿茶饮料生产中,储存期间茶汤的沉淀生成和色泽劣变是制约纯茶饮料发展的技术障碍,至今仍未得到解决。本文以绿茶为试材,从茶汤的化学成分和体系的物化性质两方面探讨了茶汤沉淀形成的机理。对沉淀形成过程中茶汤流变特性、沉淀颗粒形态变化、电解质和氢键裂解剂的作用、红外光谱变化等内容进行了研究,结果表明,茶汤为牛顿流体;沉淀形成过程中,粒径逐步增大,形成不规则形态的团块状,初步判定经低温储存后的茶汤体系介于胶体分散系和粗分散系之间;茶汤颗粒间的氢键、静电作用是影响茶汤沉淀形成的因素,共价键不是沉淀形成的主要因素。通过引入胶体热动力学中的“相界”概念,分别判断了茶汤中各主要成分进入上清相和沉淀相的趋势,结果表明,茶多酚是构成茶汤沉淀物的主体物质,其次是果胶、咖啡碱,而在沉淀相中分配系数较大的成分依次是叶绿素、没食子酸、果胶、蛋白质、花青素、咖啡碱、可可碱。本研究借助有机溶剂萃取、HPLC-PDA检测、荧光分析、通径分析等方法,对绿茶汤色的主要成分及其与汤色劣变之间的相关性进行了研究。结果表明,决定绿茶茶汤色泽的不仅限于水溶性色素,脂溶性色素（主要为叶绿素和黄酮）对茶汤的绿度和黄度影响较大。通径分析结果表明,对茶汤绿度的影响因素主要是X₄叶绿素、X₂多酚;对茶汤黄度的影响因素主要是X₂多酚、X₆抗坏血酸、X₄叶绿素。比较了常规浸提、微波助提、超声波助提和添加β-CD对绿茶茶汤色泽变化以及沉淀形成的影响。结果表明,常规浸提、超声波浸提和添加β-CD浸提方式的茶汤总浸出率无显著差异,微波浸提所得茶汤的总浸出率最低;四种浸提方式对绿茶茶汤亮度L值、绿度a值无明显差异,超声波浸提所得茶汤的黄度b值较其它三种浸提方式稍高;微波浸提与加β-CD浸提的茶汤澄清度优于常规浸提和超声波浸提;常规浸提、加β-CD浸提、微波浸提和超声波浸提所产生的沉淀物分别占总固形物的9.42%、2.20%、4.78%和7.18%。从茶汤沉淀颗粒形态分析显示,β-CD加入起到了胶核作用,有利于减少茶汤沉淀物的产生。采用DSC扫描分析、紫外光谱分析、高效液相色谱等手段,研究了β-CD减少茶汤沉淀生成和稳定茶汤色泽的作用机理。研究表明,在共热搅拌条件下,β-CD可以与茶汤中茶多酚及儿茶素形成包合物。包合产物具有较好的热稳定性。β-CD处理增加了叶绿素a、b的水溶性,其溶解度与β-CD浓度成正相关。从溶胶体系的动力学原理研究了β-CD在茶饮料澄清、护色方面的作用。研究结果表明,加入β-CD导致茶汤粘度增大,沉淀粒径减小,临界聚沉浓度增大,减缓了粒子在重力场中的沉降速度。加入β-CD还抑制了茶汤中氧气的溶解能力,减缓了氧气存在对茶汤品质的不良影响。从溶胶的动力学稳定性角度解释了β-CD提高茶汤稳定性的机理。更多还原

【Abstract】 Sediment formation and color distortion during the storage of green tea beverage affected its quality,and become key obstacles to the poduction of green tea beverage.The mechanism of sediment formation in green tea beverage were studied based on the chemical elements and infusion system in green tea extraction.The viscosity character, micrograph of tea cream particles and IR spectrum of tea infusion were compared between orginal tea infusion and stored tea infusion.Effects of NaCl on turbids of tea infusion and guanidine hydrochloride on the viscosity of tea infusion were also investigated in this thesis.The results showed that the tea infusion belonged to the Newton fluid.The hydrogen bond and ion bond in tea infusion system contributed to sediment formation, while covalent bond was not a major factor for sediment formation.And green tea infusion stored at low temperature was between the colloid phase and dispersed phase,which was confirmed according to the shape of tea cream particles.An effective distribution coefficient K_A was introduced in this study to estimate the diffusing tendency of components in tea infusion to supernate phase or sediment phase. The results showed that polyphenol was the main component contributed to the sediment formation,and protein and caffeine in turns.However,K_A of main components in green tea infusion showed that the primary components affected the sediment formation was taken turns as chlorophy,gallic acid,pectin,protein,anthocyanin anthocyanin and caffeine.And K_A of polyphenol,amino acid,and catechins were less than 1.0,which implied that the stability of tea infusion could be improved by changing some characteristics of those components.The relationship between the color distortion and the change of main components during the storage period of tea infusion was studied by means of the methods of organic solvent extraction,HPLC-PDA detection,fluorescence emission decay traces and pathway analysis.It showed that the greenness of tea infusion increased after the lipid-soluble pigments were separated,which implied that the lipid-soluble pigments (mostly chlorophyll and flavone) were as important as water-solubility pigments for greenness of tea infusion,especially for greenness and yellowness.Pathway analysis indicated that chlorophyll and polyphenol contributed to greenness of tea infusion,and that polyphenol,ascorbic acid and chlorophyll to yellowness. Effects of different extracting methods,such as conventional extraction,microwave extraction,ultrasonic extraction and addingβ-CD extraction,on the sediment formation and color distortion of tea infusion were compared.The yields of solid extraction in ultrasonic extraction and addingβ-CD extraction had no significant difference compared with conventional extraction.And the color of tea extraction were no significant difference between different extracting methods.The tea infusions extrcted by microwave extraction and addingβ-CD extraction showed higher clarity and formed littler cream than ultrasonic extraction and conventional extraction during storage period.The ratio of cream to solid yields in conventional extraction,addingβ-CD extraction,microwave extraction and ultrasonic extraction were 4.78%,2.20%,7.18%and 9.42%,respectively.The morphology of tea cream particles extracted by addingβ-CD appeared regular size and shape and was similar to that ofβ-CD.It suggested that addingβ-CD provided colloid cores for tea cream and improved the stability of tea infusion.The mechanism ofβ-CD to prevent tea infusion from sediment formation and color distortion was investigated by means of DSC-scan,UV-scan and HPLC analysis.The results showed that catechins could interacte withβ-CD and then formed complexes under the condition of co-evaporation-stirring,which improved the therm stability of catechins. Chlorophyll also could interacte withβ-CD,which enhanced its solubility in aqueous solution.Effects ofβ-CD on the clarification and color of tea infusion was studied by using dynamic mechanism of colloidal.The results showed that addingβ-CD increased the viscidity of tea infusion and the coagulation value of NaCl,decreased the particle size and sedimentation rate.Addingβ-CD could lower the oxygen dissolubility in tea infusion.更多还原