Inhibitory Mechanism Of Apple Young Fruit Polyphenols On ?-amylase And Preparation Of Composite Nanoparticles

China is the world's largest apple producer,and its output and planting area rank first in the world.However,in the process of apple growth,in order to ensure the yield and quality of apples,farmers will thin the fruit trees,so a lot of thinned-young apples are directly discarded in the orchard,causing a lot of waste.However,the thinnedyoung apple contains 10 times more polyphenols than the mature apple and thus can be used as a potential,easily available source of polyphenols.In this study,five young apple cultivars,Short-branch Fuji,Pink Lady,Jinshiji,Ruiyang,and Qinyang,were used as materials to be researched.Their polyphenol contents and antioxidant capacities were compared.Enzymatic kinetics,fluorescence spectroscopy,Thermal analysis and eversion methods were used to explore the mechanism of their inhibition on ?-amylase.Fluorescence quenching,Fourier-infrared spectroscopy,circular dichroism,and other analytical methods were used to analyze the interactions between YAP and zein,and to explore the effects of YAP on the emulsion antioxidant and storage period,in order to broaden the application of thinned-young apple in the field of food colloid.The main research contents and conclusions of this article are as follows:(1)A total of 14 polyphenols were separated from YAP,mainly phlorizin,chlorogenic acid and proanthocyanidin B2.The cultivar with the highest polyphenol content was Short-branch Fuji,with the value of 489.59 mgGAEs/g.The highest FRAP clearance and DPPH clearance of all YAP varieties was Jinshiji YAP,which were 877.78 ?mol/L Fe2+,93.89%respectively,and it had the smallest IC50 value of 0.023 mg/mL,which means that it owns the highest enzyme inhibitory activity.The highest ABTS clearance of all YAP varieties was Pink Lady YAP,which was 71.61%.From the further correlation analysis between monomer phenol and IC50,it was found that the difference between young fruit varieties was mainly caused by the content of monomer phenol.The higher the content of proanthocyanidins B1,4-p-coumarinylquinic acid,quercetin 3-O-glucoside and total tannin were found in YAP,the higher the ?-amylase inhibitory activity the YAP showed.(2)The type of inhibition on PPA was competitive inhibition.It was found that the order of 1/Kic and IC50 values of YAP were the same,both were Jinshiji>Short-branch Fuji>Pink Lady>Ruiyang>Qinyang.YAP significantly reduced the fluorescence intensity of PPA,and the higher the YAP concentration was,the stronger the fluorescence quenching effect it happened.The order of the KFQ values of YAP was:Jinshiji>Short-branch Fuji>Pink Lady>Ruiyang>Qinyang.The order of KFQ is opposite to the order of IC50 values,which means that the stronger the fluorescence quenching reaction is,the stronger the inhibitory effect YAP owns.YAP caused a significant decrease in Td and ?H of PPA,which led to a decrease in the thermal stability of the enzyme.The maximum emission wavelength of PPA exhibited red shifts to different degrees.According to the red shift results,it can be found that the order of potential expansion of PPA structure combined with YAP was:Jinshiji=Pink Lady>Short-branch Fuji=Qinyang>Ruiyang.Intestinal eversion experiment found that YAP can significantly reduce the intestinal glucose digestion content in vitro.YAP,chlorogenic acid,and tannin showed inhibition of SGLT1 and GLUT2 activity,hindering glucose absorption.Therefore,YAP can be used as a good amylase inhibitor and blood glucose inhibitor,and has the potential to develop related drugs for the treatment and prevention of diabetes.(3)At pH=4,zein and YAP can form stable zein-YAP nanoparticles(ZYP)with a particle size between 142 and 261 nm by antisolvent method.YAP reduced the fluorescence intensity of zein and produced mixed quenching effect.Fourier-infrared transform analysis and circular dichroism analysis revealed that the two compounds formed a complex through hydrogen bonding interaction and hydrophobic interaction,and the folded structure of the peptide chain was opened.The composite particles were used as an emulsifier to prepare an emulsion,and the emulsification stability of emulsion was improved by 52.3%-61.2%.Emulsifying activity of the emulsion was increased to 61.8%-74.0%.The clearing rates of emulsion of DPPH and ABTS reached 62.3%and 66.4%respectively.After 12 days,the POV of oil and fat decreased by 34.1%-47.6%.Therefore,zein-YAP nanoparticles can adjust the properties of the emulsion,have good effects on lipid antioxidant and free radical antioxidant activities,and can be further used as a complex emulsion in the food industry.In summary,based on the existing research on YAP,this study studied the polyphenol composition,antioxidant activity,and ?-amylase activity and inhibition mechanism of five varieties of YAP,and analyzed the regulating effect of zein-YAP to the emulsion,which provide data support and new ideas for the application of young apples in the food industry.