Analysis Of Physicochemical Characteristics Of Green Tea Beverages Made From Different Tea Varieties And Exploration Of Precipitation Factors Interaction Mechanism

With the development of economics and the accelerated pace of life,tea beverage with its healthy,natural,stylish and convenient properties is gradually attracting attention,becoming a fast-growing health beverage in recent years.The current market share of pure tea beverage in the tea market is small,because high-quality pure tea beverage producing has many problems,such as the selection of raw materials,processing and quality maintenance.These problems serious ly affect the consumer’s preferences and the stability of tea beverage.The quality of green tea beverage mainly includes stable colors,full fragrance and anti-precipitation.Precipitates not only affect the appearance of the product,but also can easily lead to flavor decline of product.It is an important factor restricting the development of market.As the precipitation formation process is complex and so far the formation mechanism and adjusting methods lack a clear study,the aim of this paper is to select the tea varieties suitable for the development of green tea beverages in C hongqing;to explore the interaction mechanism between protein and other chemical components involved in precipitation;to improve the theoretical basis for regulating the formation and development of high quality pure tea beverages.The main findings are as follows:1.Baked green teas made from fresh leaves of 18 varieties were chosen to make green tea beverage.The changes of physicochemical characteristics(transmittance,particle size,precipitation capacity and principal biochemical components)of 18 kinds of green tea beverages after 30 days of storage were studied.The results showed that: 1)there was significant difference in the clarification degree of green tea beverage in different tea varieties.The transmittance of green tea beverages decreased from 77.1%~84.5% to 62.7%~72.9%.The particle size increased from 476.1~538.1 nm to 586.4~669.7 nm,and the precipitation capacity increased from 46.7~80.0 mg/L to 193.3~473.3 mg/L.Sichuanquntipinzhong and Mingshantezao had relatively high quantities of tea cream;Fudingdabaicha and Fudingdahao had relatively middle quantities of tea cream;Meizhan,Q ingxinwulong and Menghaidayezhong had relatively low quantities of tea cream.As a result,green tea beverage made from Qingxinwulong,Meizhan and Menghaidayezhong should have best clarification degree and stability.2)there were significant differences in the principal biochemical components of different tea varieties.Because of the formation of tea cream and oxidative degradation,except for catechin,the contents of tea polyphenols,free amino acids,total soluble sugar,soluble protein,caffeine,epigallocatechin,epigallocatechin gallate,epicatechin,gallocatechin gallate,epicatechin gallate all decreased.The reduction ratio of tea polyphenols,caffeine and soluble protein were higher than that of free amino acids and total soluble sugar,and the reduction ratio of epigallocatechin gallate,epigallocatechin and epicatechin gallate was higher than that of epicatechin and gallocatechin gallate.3)according to Pearson correlation analysis,contents of tea polyphenols,caffeine,epigallocatechin gallate,total soluble sugar and soluble protein were significantly or highly significantly positively correlated w ith the clarity change in green tea beverage.2.Based on the research results above,three tea varieties with low(Sichuanquntipinzhong),middle(Fudingdabaicha)and high(Meizhan)clarity were selected as the raw material to make green tea beverage and the changes of color,clarity and principal biochemical composition of selected green tea beverage stored for 0~180 d were measured to systemically evaluated tea varieties suitable for developing green tea beverage.The results showed that: 1)The L* values and transmittance of the green tea beverage significantly decreased after 180 days of storage,and the color parameters a* and b*,particle size and precipitation capacity significantly increased too,indicating that the clarity significantly decreased and the color turned red and yellow significantly,which meant the green tea beverage become turbid and brown in storage.Considering the values and changes of L*,a*,b*,transmittance,particle size and precipitation capacity,the clarity and color of Meizhan were relatively good,and it is suitable for developing green tea beverage.2)After 180 days of storage,except for catechin and flavone,the contents of tea polyphenols,free amino acids,total soluble sugar,soluble protein,caffeine,epigallocatechin,epigallocatechin gallate,epicatechin,gallocatechin gallate,epicatechin gallate all decreased.The contents and changes of the principal biochemical components such as tea polyphenols,total soluble sugar,caffeine,epigallocatechin gallate and epicatechin gallate in Sichuanquntipinzhong were relatively high,which indicated tea cream phenomenon was relatively significant.The clarity and color of the green tea beverage made from Sichuanquntipinzhong was much worse than the other two varieties’.But from a nutritional prospective,the contents of principal biochemical components of Sichuanquntipinzhong were relatively higher,indicating that it has a better taste and health function.3.Biochemical components have an important role in tea cream formation for green tea beverage,including catechins,caffeine,soluble protein,total soluble sugar,etc.Structuring the simulation systems of catechins-protein,caffeine-protein and soluble sugar-protein,and using fluorescence spectroscopy and ultraviolet absorption spectroscopy to respectively explore and compare interaction mechanism of catechins,caffeine and soluble sugar with protein from molecular level.The results showed that: 1)galactose,arabinose and glucose had no effect on the endogenous fluorescence of BSA,that is,these three monosaccharides did not interact with protein.epigallocatechin gallate,epicatechin gallate,epigallocatechin,epicatechin and caffeine had obvious quenching effect on the endogenous fluorescence of bovine serum albumin,and the quenching mode was static quenching.Through the ultraviolet absorption spectroscopy,it can be further explained that catechins and caffeine can combine with bovine serum albumin and produce a new complex.2)The binding constants(Ka)of epigallocatechin gallate,epicatechin gallate,epigallocatechin,epicatechin and caffeine with bovine serum albumin were: 13.20×107,8.94×107,1.56×107,1.10×107,3.64×104 L/mol respectively;the number of binding sites(n)were 1.32,1.30,1.19,1.17,1.12 respectively.The catechins have more phenolic hydroxyl,so their binding constants and number of binding sites were higher than those of caffeine.Based on the binding constants and number of binding sites,it was found that the order of binding ability with bovine serum albumin was: epigallocatechin gallate> epicatechin gallate>epigallocatechin>epicatechin>caffeine.3)the binding position of epigallocatechin gallate,epicatechin gallate,epigallocatechin,epicatechin,caffeine with bovine serum albumin were located in the vicinity of tryptophan residues and tyrosine residues by synchronous fluorescence analysis,and the binding position was closer to tryptophan residues.