| 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. |
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