Molecular Aggregation In The Formation Of Green Tea Cream

Tea is a natural health drink given by nature,however,c hemical componentsin natural tea infusionswere not completely free,many components could interact to form nano-colloidal particles with different sizes.Toexplore the molecular aggregate mechanism in the formation of green tea cream,green tea from Camellia ptilophylla and Camellia sinensis were used,from the new perspective of nano-aggregates,the effects of extract condition,methylxanthines and metal ions on the formation and stability of nano-aggregates in green tea were studied by changing extract condition,add ing different kinds and concentrationmethylxanthines and metal ions to tea infusions,initially revealed the structure-effect and count-effect of methylxanthines-catechin interaction by constructing simulated tea system,initially analyzed nano-aggregates proteincomposition characteristics by separating and purifying the tea nano-aggregates proteins,combined multiple methods from phytochemistry,colloidal chemistry,nuclear magnetic resonance spectroscopy,electrophoresis,liquid chromatography and amino acid automatic analyzer,gradually exploring the formation mechanism and stability of the nano-aggregates in green tea,the main results were as follows:（1）The extraction conditions of tea leaves had a significant effect on the formation and stability of green nano-aggregates.Results show that:The amount of colloidal particles greatly improved and more concentrated wtih extract time extended to 8⁴0 min;85℃was a critical extraction temperature,various components of green tea continue to leach and transfer to nano-aggregates with increase of extraction temperature,main nano-aggregates were formed,the electrostatic stability between particles decreased;when tea radio decreased to 1:50,various components of green tea significantly transfer to nano-aggregates,amount of nano-aggregates increased significantly,and the electrostatic repulsion between particles decreased;The protein,methylxanthines and gallate-catechins in tea infusion significantly affected the formation and stability of nano-aggregates.（2）The affinity of caffeine with other components in tea infusion was stronger than that of theobromine and theophylline,which plays an important ro le in the formation and stabilization of nano-aggregates.Results show that:（1）Adding caffeine or theobromine could increase the average diameter and the amount of colloidal particles,but not the theophylline.For green tea from Camellia ptilophylla,the average particle size of nano-aggregates increased and the number of colloidal particles decreased with adding 1⁵ mM caffeine;for green tea from Camellia sinensis,the average diameter was increased significantly and the number of colloidal particles decreased with adding 5¹0mM caffeine,indicating that former was more susceptible to the caffeine than latter.（2）Components of green tea from Camellia ptilophylla（tea polyphenols,protein,soluble sugar,gallato-catechins,nongallato-catechins）were more susceptible for caffeine than those from Camellia sinensis（gallato-catechins,theobromine）,and transferred to the nano-aggregates.Building a simulated system with different catechins and caffeine,NMR analysis showed that EGCG interacted with caffeine mainly through gallic acid,and the position and number of methylation in methylxanthines had an effect on the interaction with EGCG,the more the number of methyl groups,the greater the impact on the interaction between the caffeine and EGCG.（3）The effect of metal ions on the stability of colloidal particles of green tea was:CaCl₂>MgC l₂>NaCl,mainly by neutralizing the surface charge of colloidal particles,reducing the electrostatic repulsion and causing flocculation,then promoting the main chemical components tonano-aggregates.Results show that:（1）The addition of divalent metal ions could significantly increase the ratio of charged ions,reduced the surface charge of particles and promoted to flocculation,and the flocculation promoteof Ca²⁺was stronger than Mg²⁺,the amount of colloidal particles increased with the increase of CaC l₂concentration.（2）The addition of divalent metal ions,especially Ca²⁺,could promote the main chemical components transfer to the nano-aggregates,with the increase of CaC l₂concentration,the nano-aggregates distribution of chemical components tends to increase.Building a simulated system with different metal ions and EGCG,caffeine,NMR analysis showed that CaC l₂,MgC l₂ and NaC l had no interaction with caffeine and EGCG.（4）The molecular weight composition of the nano-aggregates crude protein of the green tea was complex,and the amino acid composition was relatively complete.The molecular weight of nano-aggregates protein in the green tea from Camellia ptilophylla were 30¹00 k Da,and 23 kinds of proteins were identified.For green tea from Camellia sinensis,The molecular weight of the nano-aggregates protein was mainly in the85¹20 kDa and 25⁶0 kDa,and 198 kinds of protein were identified.Two kinds of green tea nano-aggregate were composed of 17 kinds of amino acids,and the hydrophobic amino acids in the nano-aggregates accounted for 30% approximately.