Research On Extraction Kinetics Of Tea Polyphenols And Its Compositions

In this master's thesis, with yellow pill made by one bud and four leaf in summer and autumn as material, five different techniques to juice processing were designed with ratios of tea to water 1:1.5,1:1.75,1:2.0,1:2.25 and 1:2.5 respectively. By juicing, tea polyphenols, amino acids, water extract and other main compositions were devided into two parts:part of leaching into tea juice, constitute its main taste components; part of the reserves in wet tea-leaf, dried after processing, make processing sample main containing components. Tea polyphenols,amino acids and other compositions in five groups of processing tea juice, processing samples were measured. Results showed that sample handling of tea/water 1:2.25 retained the most tea polyphenols; ratios of EGCG, ECG, GC, EGC etc catechin monomers to water extraction were highest in sample handling of tea/water 1:1.5, with high concentration, lower TP/AA and better fresh cool degrees in tea juice. On the basis of comprehensive comparation,1:1.5 of juice processing was optimum.1:1.5 of juice processing was conducted on tea sample (original CK), concentrations of tea polephenols, amino acid, water extract in tea juice obtained were 17.5mg/ml,5.5 mg/ml,66.2 mg/ml respectively, and the ratio of polephenols to amino acid was 3.19. Contents of tea polephenols, amino acid, water extract, total catechins, catechin monomers in CK and processing sample were measured, and dynamic changes of ratios of tea polephenols to amino acid (TP/AA), tea polephenols to water extract (TP/WE), amino acid to water extract (AA/WE), total catechins to water extract (CC/WE) were researched. Results showed that by juice processing, TP/AA increased from 6.20 to 7.20, TP/WE increased from 0.437 to 0.483, AA/WE declined from 0.071 to 0.067, and CC/WE increased from 0.237 to 0.241. Comparation of four main catechin monomers EGC, GC, EGCG, GCG especially EGC, EGCG with water extract in processing sample were higher than CK. By juice processing, high concentration and fresh cool degree of tea juice could be attained, while tea polephenols, catechins etc components were pre-concentrated, with relative contents improved, which was good for purification process after extracting.With tea/water 1:20, temperature 100℃, dynamics of tea polyphenols, total catechins and catechin monomers during 45min extraction in CK and processing sample were measured, and rate constant Kobs was calculated by a steady-state model. Extraction dynamics of trans catechin and epicatechin monomers were compared, with relevant mechianism discussed. Results showed that polyphenols and total catechins in both samples reached extraction quilibrium after 20min. The extraction rate of epicatechin monomers in CK achieved the biggest at 20min, then descended with time, EC, EGC more obviously; However, extraction rate of epicatechin monomers in processing sample remained steady after reaching equilibrium. The extraction rate of trans catechin monomers in both samples increased steadily with time, achieving the highest value at the end of extraction. The leaching speed of main components in treatment sample was significantly higher than CK.In the long period and high temperature extraction environment, epicatechins would easily occur isomerization reaction, generating trans catechins because of higher internal energy. In some cases, isomers could serve as one kind of functional composition for similar physiological activity. Ratios of sum of GC and EGC, EGCG and GCG to tea polyphenols in processing sample reached the peak value at 4-5min, while this two ratio of CK reached maximum at 10-20min, both of the peak value had no obvious difference between two samples. Comprehensive considering, processing sample was obviously superior to CK in short-term efficient access tea polyphenols and other components, preparation tea polyphenols crude product rich in GC,EGC, EGCG, and GCG.