Study On The Bioavailability Of Non-extractable Polyphenols From Tea

Tea polyphenols are the material base for the diversified bioactivity of tea,and also an important component of the unique flavor and taste of tea.Non-extractable polyphenols are the non-extractable fraction in aqueous and organic solvent or bound to macromolecules such as dietary fiber and also the main component of dietary polyphenols,and hence have been ignored in currently polyphenolic research.In the present study,response surface methodology(RSM)was used for optimizing tea polyphenols extraction conditions.The extractable and non-extractable polyphenols(EPP and NEPP)of teas with different levels of fermentation of tea were characterized by HPLC profiling and chemometrics.Furthermore,DPPH radical scavenging activity(DPPH assay),ABTS radical scavenging activity(ABTS assay)and ferric-reducing antioxidant power(FRAP assay)of EPP and NEPP in different levels of fermentation of tea were investigated.In addition,an in vitro digestion of tea was performed to evaluate the bioaccessibility of tea polyphenols.The main results are showed as following.1.Plackett-Burman design(PBD),Steepest ascent method(SA)and Box-Behnken design method(BBD)were used to optimize the optimal extraction conditions of tea polyphenols,and HPLC was used to detect the tea polyphenolic profile extracted by semi-bionic extraction tea.Finally,the antioxidant activity of tea polyphenols was studied.The results showed that the optimal extraction conditions for semi-bionic extraction were liquid-solid ratio 110:1,extraction time 32 min,extraction 2 times,ultrasonic power 310 W.Under this condition,the extraction efficiency of TPC(124.93±4.14 mg GAE/g DW)was significantly higher than conventional water extraction(109.11±2.13mg GAE/g DW)under the same conditions.At the same time,TPC obtained by semi-bionic extraction had higher antioxidant activity than conventional water extraction.In addition,semi-bionic extraction was extracted high antioxidant activity of EGCG and ECG,and increased by 83.37%and 60.06%,respectively.2.The EPP and NEPP in different levels of fermentation of tea were extracted by hot water extraction and alkali extraction,respectively.Then the contents and composition of EPP and NEPP in teas were evaluated by HPLC.Finally,the antioxidant activities of EPP and NEPP in different levels of fermentation of tea were determined.The results showed that the EPP content of tea decreased with the increase of processing fermentation degree.Unfermented tea and post-fermented tea contained less NEPP,and the EPP content of tea is about 5 times higher than that of NEPP.The main components of EPP in different levels of fermentation of tea were EGC,EGCG,CAF,EC and ECG,while the main components in NEPP were GA,C and EGCG.EPP in unfermented tea(LJ and BLC)showed the highest antioxidant activity,while NEPP in unfermented tea and post-fermented tea showed the less antioxidant activity.The content of polyphenol and antioxidant activity in different levels of fermentation of tea were positive correlation.3.After the brewing of different levels of fermentation of tea,the content of tea polyphenols dissolved decreased with the increase of the level of fermentation,and 55%-75%of tea polyphenols could be soaked after 3 times of brewing.After oral,gastric and intestinal digestion,the release of tea polyphenols gradually reduced from different levels of-fermentation of tea soup,while the main release of tea polyphenol of different levels of fermentation of tea residue was in gastric digestion.Different levels of fermentation of tea powder polyphenol was gradually released in vitro digestion and eventually released 40%-70%of tea polyphenols.The main polyphenols released by in vitro digestion of tea powder are GA,EGC,EGCG,EC and ECG,while released less GC,C and GCG.The digestion of tea soup mainly released GA,GC and C,and tea polyphenol released from tea residue digestion was almost none.Light fermented tea(green tea and white tea)showed higher antioxidant activity after digestion,while the higher-fermentation tea digestive juice had lower antioxidant activity.Different level of fermentation of tea digestive juice antioxidant activity and the content of tea polyphenol was showed positive correlation.