Effects Of Rancidity On Antioxidant Properties Of Rice Bran Dietary Fiber And Its Binding Polyphenols During In Vitro Digestion

Our country is very rich in rice bran resources,with an average annual output of more than 14 million tons.Rice bran contains 34-52%dietary fiber and 9.60-81.85 mg GAE/g polyphenols,which is a high-quality resource for preparing dietary fiber and polyphenols.Natural polyphenols are often combined with dietary fibers,and the interaction between dietary fiber and polyphenols is closely related to the structure and properties of polyphenols and dietary fibers.Rice bran is easily rancid,and the rancidity of rice bran will change the structure and properties of rice bran dietary fiber and polyphenols.The changes in the structure of rice bran dietary fiber and phenols under the environment of rice bran rancidity will inevitably lead to changes in dietary fiber-polyphenol interactions,thereby affecting the antioxidant properties of rice bran dietary fiber and its bound polyphenols.Therefore,in this paper,the effect of rice bran rancidity on the content of phenolic substances in different forms in rice bran dietary fiber was detected,the effect of rice bran rancidity on the composition and content of free phenols released during in vitro digestion of rice bran dietary fiber was studied,the effect of rice bran rancidity on the free radical scavenging ability and cellular antioxidant capacity of rice bran dietary fiber in vitro digestion products was explored,and the correlation between the antioxidant activity of rice bran dietary fiber in vitro digestion products and the content of phenolic substances in the digestion products was analyzed.The fresh rice bran was stored for 0,1,5,7,and 10 days and then defatted to prepare rice bran dietary fiber.The bound phenols in different forms were extracted from the dietary fiber of rice bran,and the content of the bound phenols in different forms was detected.The results showed that rice bran storage would lead to rapid rancidity of rice bran.When the rice bran storage time increased from 0 days to 10 days,the acid value of rice bran crude oil increased from 5.08 mg KOH/g to 61.30 mg KOH/g.When the storage time of rice bran increased from 0 days to 10 days,the total phenolic content in rice bran dietary fiber gradually increased from 7.78 mg GAE/g to 10.83 mg GAE/g;the content of soluble ester-bound phenol and insoluble glycoside-bound phenol also increased gradually,from 0.81 mg GAE/g to 1.22 mg GAE/g and 1.08 mg GAE/g to 3.28 mg GAE/g,respectively;the content of soluble glycoside-bound phenol and insoluble ester-bound phenol increased first and then decreased.It indicated that rice bran rancidity would lead to changes in the interaction between rice bran dietary fiber and phenolic substances.By simulating gastrointestinal digestion in vitro,the composition and contents of free phenols released during in vitro digestion of rice bran dietary fiber prepared from rice bran stored for different times was detected.The study found that in the gastric digestion stage,with the increase of the storage time of rice bran,the content of free caffeic acid,p-coumaric acid,ferulic acid and methyl caffeate in the digestive products gradually decreased,while the content of quercetin gradually increased;With the increase of gastric digestion time,the content of caffeic acid in the digested products gradually decreased,the content of p-coumaric acid,methyl caffeate and quercetin generally increased,while the content of ferulic acid had no significant change.During the intestinal digestion stage,a new phenolic acid,isoferulic acid,appeared in the digestion products of dietary fiber from rice bran.With the increase of storage time of rice bran,the contents of caffeic acid and methyl caffeate in the in vitro intestinal digestion products of rice bran dietary fiber first decreased and then increased,the content of ferulic acid and p-coumaric acid released from rice bran dietary fiber prepared from rice bran storage for 7 days was the most during in vitro intestinal digestion.With the increase of intestinal digestion time,the content of methyl caffeate in the digestive products decreased significantly,the content of ferulic acid,p-coumaric acid and isoferulic acid increased gradually,and the content of caffeic acid released during in vitro intestinal digestion varied.The rice bran dietary fiber was subjected to simulated gastrointestinal digestion in vitro,and the changes of antioxidant properties of the rice bran dietary fiber prepared from rice bran with different degrees of rancidity during the in vitro digestion were studied.In the gastric digestion stage,with the increase of rice bran storage time,the free radical scavenging ability and ORAC of rice bran dietary fiber in vitro gastric digestion products gradually weakened.In the intestinal digestion stage,with the increase of the storage time of rice bran,the ABTS+·scavenging ability of rice bran dietary fiber in vitro intestinal digestion product was the largest when rice bran was stored for 7 days,while the ·OH scavenging ability,the O2-·scavenging ability and ORAC first weakened and then strengthened.With the increase of digestion time,the free radical scavenging ability and ORAC of gastrointestinal digestion products of rice bran dietary fiber was gradually enhanced.The antioxidant capacity of rice bran dietary fiber in vitro gastric digestion products was positively correlated with the contents of ferulic acid,p-coumaric acid and methyl caffeate in the digestive products,and negatively correlated with the content of quercetin.The antioxidant capacity of rice bran dietary fiber in vitro intestinal digestion products was positively correlated with the contents of p-coumaric acid and ferulic acid,and negatively correlated with the contents of methyl caffeate and isoferulic acid.A H₂O₂-injured HUVEC cell model was established.The morphology of HUVEC cells was observed by H&E staining and Hoechst staining,and it was found that the number of HUVEC cells protected by in vitro digestion products of rice bran dietary fiber increased and the cell morphology was more intact.Compared with the injury group,the content of ROS in the protection group of rice bran dietary fiber digestion products decreased,the activity of SOD increased,and the content of MDA decreased,indicating that the in vitro digestion products of rice bran dietary fiber had good cellular antioxidant activity.And with the increase of the storage time of rice bran,the contents of ROS and MDA in the cells in the protection group of the in vitro gastric digestion products of rice bran dietary fiber gradually increased;the content of ROS in the cells of the protection group of the in vitro intestinal digestion products of rice bran dietary fiber increased first and then decreased,the activity of SOD first decreased and then increased,and the content of MDA increased gradually.