Stability And Antioxidant Activity Of Phenolic Compounds During In Vitro Digestion

Phenolic compounds are important secondary metabolites synthesised by plants.They have many biological activities,such as antioxidation,antitumor,and can also inhibit the occurrence of cardiovascular disease,inflammatory disease and cancer.In vivo,the effect of phenolic compounds depends largely on their stability and biological activity after digested.At present,researches mainly focus on phenolic compounds in the food matrix or extract,and there are few studies on the standards.In this study,32 phenolic compounds with typical structure were studied to explore their changes of stability and antioxidant activity during in vitro digestion.This study aimed at providing ideas and data basis for the exploration in complex food matrix and establishment of comprehensive evaluation method for antioxidation.The main research results were as follows:1.32 phenolic compounds were processed with in vitro digestion model included three steps(oral,gastric and intestinal digestion).The changes of phenolic structure and content at different digestion phases were determined by UPLC and UPLC-QTOF-MS/MS.The results showed that most phenolic compounds degraded after oral phase.After gastric phase,phenolic compounds remained relatively stable and the contents would not decrease further.Phenolic contents were reduced sharply after intestinal digestion.Ferulic acid,p-coumaric acid and sinapic acid had new isomer peaks found in the UPLC graph after digested.The bioaccessibilities of phenolic compounds with different structures were diverse.There were certain rules between structure and stability.The average bioaccessibility of different phenolic compound was as follows:flavanone(70.15%)>phenolic acid(47.06%)>flavonol(21.90%)>flavone(20.45%)>flavanol(ND).2.DPPH,ABTS,FRAP and ORAC assays were used to determine the chemical antioxidant activities of 32 phenolic compound samples and samples at different digestion phases.The results showed that there were structure-activity relationships of phenolic compounds assessed by DPPH,ABTS and FRAP methods.The results of ORAC method were different from others.After in vitro simulated digestion,the chemical antioxidant activities of most phenolic compounds were decreased,except for some phenolic compounds with minimal antioxidant capacity initially.The change trends of antioxidant activity during in vitro digestion were multiple using different chemical methods.In general,the change trend of the chemical antioxidant activity was consistent with content.3.The cellular antioxidant activities of 32 phenolic compounds and digestive productions at three digestion phases were determined.The results showed that there were structure-cellular antioxidant activity relationships of phenolic compounds.In the oral and gastric phases,the change of cellular antioxidant activity was consistent with phenolic content and chemical antioxidant activity.After intestinal digestion,the cellular antioxidant activities of phenolic compounds with diverse structures showed various trends.After in vitro simulated digestion,the cellular antioxidant activities of most phenolic compounds were decreased,except for flavanones and some phenolic acids with low cellular antioxidant capacity initially.4.The Pearson correlations between various antioxidant evaluation methods were calculated.It was found that there were reliable correlations between digested cellular antioxidant activity assay and chemical methods.By fitting with Matlab software,three antioxidant activity prediction equations of phenolic acids,flavones and flavanones,flavanols and flavanols were established.Through the verification of equations,it was shown that the fitting equation of phenolic acids could accurately predict the digested cellular antioxidant activity.The other two equations might need correction after determining the cellular absorption.