Study On The Intensified Extraction Of Polyphenols From Buckwheat Bran And Properties Of Their Complex

Buckwheat is a by-product of buckwheat and is usually used as feed or discarded.Buckwheat bran is rich in dietary fiber,protein,carbohydrates,vitamins,polyphenols and other types of nutrients,of which the polyphenol content is about 0.5%-2%.It is a natural source of polyphenols.As a functional ingredient,polyphenols have strong antioxidant capacity and are effective in the prevention and treatment of diabetes,hyperlipidemia,cardiovascular and atherosclerosis diseases.However,the molecular structure of polyphenols is often unstable,resulting in low bioavailability,which has become one of the major problems limiting the application of polyphenols.In this study,to improve the overall utilization of buckwheat bran,and enhance the stability and activity of buckwheat bran polyphenols,buckwheat bran was treated by roasting,superheated steam,enzymatic hydrolysis,microwave,extrusion,ultrasonic and steam explosion respectively.The content of polyphenols was determined by the Folin-Ciocalteu method,the identification and quantification of polyphenols were determined by high performance liquid chromatography,the antioxidant activity was determined by ABTS,DPPH and FRAP assays,the antibacterial activity was estimated by the minimum inhibitory concentration,the minimum bactericidal concentration and the growth curve of E.coli and S.aureus,and the in vitro hypoglycemic activity was determined by theα-amylase inhibition experiment.The effect of pretreatment on the release of polyphenols,polyphenols composition and their biological activities in buckwheat bran was explored.The representative polyphenols quercetin and rutin were selected and cross-linked with chitooligosaccharide(COS)respectively to form a complex,and the preparation process of the complex was optimized according to the encapsulation efficiency index.The molecular structure of the complex was analyzed by SEM,TGA,UV-vis,FTIR and~1H-NMR methods,and the antioxidant activity,antibacterial activity and solublity of the complexes and their effects on glycolipid metabolism and gut microbiota in diabetic mice were evaluated,in order to comprehensively elucidate the mechanism of COS on the stability and activity of buckwheat bran polyphenols.The results showed that(1)compared with the untreated group,seven pretreatments destroyed the rigid structure of the buckwheat bran cell wall to different degrees and promoted the dissolution of polyphenols.The total polyphenol content in descending order was as follows:roasting group>superheated steam group>enzymatic hydrolysis group>microwave group>extrusion group>ultrasound group>steam explosion group.Roasting treatment increased polyphenol content of buchwheat bran the most,the free polyphenol were 1.87-folds of that of the untreated group(P<0.05).The main polyphenols in buckwheat bran were identified as rutin,quercetin,gallic acid,catechin,vanillic acid,syringic acid,ferulic acid,sinapic acid,p-hydroxy acid,benzoic acid,epigallocatechin gallate,caffeic acid,hypericin and resveratrol,a total of 13 polyphenol.(2)Compared with the untreated group,the antioxidant activity,antibacterial activity and in vitro hypoglycemic activity of polyphenols from treated buckwheat bran were improved to some extent and were positively correlated with the total polyphenol content.The antioxidant activity of polyphenols from treated buckwheat bran ranked from high to low was as follows:superheated steam group>roasting group>enzymatic hydrolysis group>microwave group>extrusion group>ultrasound group>steam explosion group;the antibacterial activity of polyphenols from treated buckwheat bran against E.coli ranked from high to low was as follows:superheated steam group,roasting group>enzymatic hydrolysis group,microwave group,extrusion group>ultrasound group,steam explosion group;the antibacterial activity of polyphenols from treated buckwheat bran against S.aureus ranked from high to low was as follows:superheated steam group,microwave group,extrusion group,ultrasound group>roasting group,enzymatic hydrolysis group,steam explosion group;α-amylase inhibitory activity of polyphenols from treated buckwheat bran ranked from high to low was as follows:superheated steam group>enzymatic hydrolysis group>extrusion group>ultrasound group>roasting group>microwave group>steam explosion group.In summary,the effect of superheated steam treatment on the activity enhancement of buckwheat bran polyphenols was the best overall.(3)The polyphenol encapsulation efficiency of Quercetin-COS and Rutin-COS prepared by ionic cross-linking method were 74.65%and 74.77%,respectively.The aromatic protons of quercetin and rutin might bind with the hydroxyl groups of COS by hydrogen bonds and non-covalent forces.The combination of the complexes broke the dense crystal structure between the polyphenol molecules and makes it easier to supply hydrogen.Therefore,the complexes had better solubility,antioxidant ability and antibacterial ability compared with quercetin,rutin and COS.(4)Quercetin-COS complex had a significant effect on improving the symptoms in diabetic mice,which could promote insulin secretion and regulate blood glucose levels,and the hypoglycemic rate of the high-dose group of complex reached 43%;compared with the model control group,the TC,TG and HDL-C concentration increased significantly and LDL-C decreased significantly in the high and medium-dose groups of Quercetin-COS complex(P<0.05),which had significant lipid regulating ability;there was no significant change in SOD activity in all dose groups of Quercetin-COS complex,and the MDA concentration decreased significantly and GPX concentration increased significantly in the high and middle dose groups of the complex(P<0.05).At the experimental doses of 225mg/(kg·d)and 500 mg/(kg·d),Quercetin-COS complex could improve the antioxidant level of the organism.Pathological tissue results showed that the Quercetin-COS complex reduced the damage to the liver,kidney,pancreas and colon caused by hyperglycemia.The Quercetin-COS complex increased the short-chain fatty acid content in the feces of mice,especially increased the content of propionic acid and acetic acid(P<0.05).The Quercetin-COS complex reduced the abundance of Firmicutes and increased the abundance of Bacteroidetes in the intestine,and improved the abundance of gut microbiota in diabetic mice.Compared with quercetin and COS,Quercetin-COS complex showed more comprehensive therapeutic effects in diabetic mice.There is great potential for Quercetin-COS as functional food supplements to regulate glucolipid metabolism in type 2diabetic patients.