Extraction Optimization And Antioxidant Activity Of Bound Polyphenols From Mung Bean Skin Dietary Fiber And Its Effect On Amylase Activity

Dietary fiber and polyphenols are common nutrients in daily life,which are widely concerned by people.However,due to the great differences in their chemical properties,structural characteristics and biological activities,they are generally studied separately.At present,the research of dietary fiber is gradually deepening,and it is found that dietary fiber contains not only carbohydrates,but also some polyphenols.However,for a long time,many scholars have paid great attention to the carbohydrate components in the definition of dietary fiber that cannot be digested by the human body,but have largely ignored the polyphenols in dietary fiber.Mung bean is a crop that is both medicinal and edible.It has a refreshing taste and unique flavor.In addition to the effects of clearing heat and detoxification,preventing heatstroke and lowering blood pressure,it also has antioxidant functions.This is mainly due to the functional components in mung bean skin,which contains a large number of dietary fiber dimension and antioxidant active substances.However,mung bean skin is a waste of resources because of its special texture,high hardness,poor taste and low utilization rate.Although the physical and chemical properties and functional properties of dietary fiber derived from many agricultural and sideline products and plants have been studied by many scholars at this stage,the effects of the compounds bound in dietary fiber,especially polyphenols,have not yet been grasped.Therefore,the dietary fiber of mung bean skin was prepared from mung bean by-product.The extraction conditions of bound polyphenols were optimized by single factor experiment and response surface experiment,and the content of total phenolic acid,total flavonoid and total anthocyanin were determined.In order to explore the components and content of bound polyphenols,the components of bound polyphenols were identified by UPLC-ESI-QTOF-MS/MS and analyzed quantitatively by UPLC-ESI-Qq Q-MS/MS.In addition,three methods including DPPH free radical scavenging activity,oxygen radical absorption capacity(ORAC)measurement and peroxy radical scavenging capacity(PSC)measurement were used to comprehensively measure the in vitro antioxidant capacity of bound polyphenols.The inhibitory activity of bound polyphenols on ?-amylase and ?-glucosidase,the average particle size of amylase,fluorescence quenching and quenching types,and spatial conformation studies were also tested to illustrate the inhibitory mechanism of bound polyphenols on amylase.The main research results are as follows:(1)After completing the single factor experiment,RSM response surface design technology was used to improve the conditions,and the quadratic regression model of dietary fiber combined with polyphenols extraction process from mung bean skin was obtained.The optimum extraction process was obtained according to regression model as follows: Na OH solution concentration 8 mol/L,alkaline solution ratio 10:1,alkaline hydrolysis time 4 h,and the best extraction rate was 37.638(mg FAE/g).It can be seen that the optimal process conditions obtained by using response surface design technology to improve the extraction can well extract the bound polyphenols in the dietary fiber.(2)Using UPLC-ESI-QTOF-MS/MS qualitative analysis,39 compounds were preliminarily identified,including 12 phenolic acids and their derivatives,12 organic acids and their derivatives,6 phenolic alcohols and 2 amino acids.The UPLC-ESI-Qq Q-MS/MS method was used to determine the content of phenolic components in the bound polyphenols extracted by alkaline hydrolysis,and 9 main components were analyzed,including 6 phenolic acids,2 organic acids and 1isoflavone.DPPH method,ORAC method and PSC method were used to evaluate the antioxidant activity of alkaline hydrolyzed bound polyphenols.Combined with the results of the three tests,it was proved that dietary fiber combined with polyphenols from mung bean skin had antioxidant capacity in vitro.(3)With the increase of polyphenol concentration(0-1000 ?g/m L),the inhibition rate of polyphenol samples on ?-amylase and ?-glucosidase increased.With the addition of polyphenols at a concentration of 0.2 to 0.6 ?M,the hydraulic radius of?-amylase gradually increases as the concentration increases.When the concentration of polyphenols was higher than 0.8 ?M,the hydraulic radius of the copolymer remained basically unchanged.At the wavelength of 400?600 nm,the fluorescence intensity of ?-amylase gradually increases first and then decreases gradually when the wavelength gradually increases,and the higher the polyphenol concentration,the higher the fluorescence intensity.The fluorescence quenching of ?-amylase by polyphenols belongs to dynamic quenching.The addition of polyphenols can reduce the content of ? helix and ? sheet in the secondary structure of ?-amylase,and at the same time increase the content of ? turn and random coils to a certain extent.The results of this study show that bound polyphenols,as a part of dietary fiber,had significant effects on the antioxidant properties of dietary fiber and the inhibitory effect on amylase,which provided a certain basis for revealing the nutritional function system of mung bean skin dietary fiber,and also provides a theoretical basis for the development of high value-added products of mung bean skin dietary fiber,and provides a new idea for the in-depth study of polyphenols.