Effect Of Endogenous Acorn Kernel Polyphenols On Starch Structure And In Vitro Digestibility

Acorn belongs to the family Quercus,which is rich in polyphenols.The chemical constituents of free-phenol extract?FPE?and bound-phenol extract?BPE?of acorn kernel,and their effects on the activities of?-glucosidase,?-amylase and dipeptidyl peptidase IV were determined.UV,fluorescence and circular dichroism were used to explore the inhibitory mechanism.Meanwhile,the effects of acorn endogenous kernel polyphenol compounds on the particle structure?SEM?,crystal properties?XRD?,infrared spectral properties?FTIR?,and in vitro digestibility of acorn starch were analyzed.The obtained results are as follows:?1?The main chemical components in FPE are quercetin?10.23%?,azalea acid?3.55%?,and gallic acid?2.33%?,and the main chemical component in BPE are ellagic acid?25.31%?,gallic acid?20.44%?and ferulic acid?7.98%?.The common compounds in the extracts are gallic acid,azalea acid,citric acid,caffeic acid,succinic acid,epicatechin and trans-4-coumaric acid.?2?Acorn FPE and BPE showed anti-competitive inhibition(IC₅₀=0.584?g/m L)and mixed competitive inhibition(IC₅₀=16.583?g/m L)on?-glucosidase,respectively.Both of them changed the protein conformation of?-glucosidase.The inhibitory activities of the four major monomers on?-glucosidase were ellagic acid>quercetin>azalea acid>gallic acid.The acorn FPE and BPE showed mixed competitive inhibition(IC₅₀=5.245 mg/m L)and non-competitive inhibition(IC₅₀=1.366mg/m L)on?-amylase,while azalea acid(IC₅₀=7.937 mg/m L)and ellagic acid(IC₅₀=0.192 mg/m L)on?-amylase inhibition type are reversible non-competitive inhibition.The type of inhibition of DPP-IV by FPE and BPE was non-competitive,and the type of inhibition of DPP-IV by azalea acid(IC₅₀=0.074 mg/m L)was non-competitive.?3?The crystal forms of acorn flour,detannized acorn flour and acorn starch are all type A,and the relative crystallinity was 23.12%,27.33%and 30.6%,respectively.Tannins decreased the relative crystallinity of acorn starch.FTIR spectra showed that the 1047/1022 cm^-1of acorn flour,detannized flour and acorn starch were 1.04,1.05 and 1.08,respectively.The presence of polyphenols would reduce the short-range order of starch chains.The three-stage in vitro digestion results of simulated oral gastrointestinal digestion showed that the hydrolysis rate was acorn starch?38.32%?>detannized flour?32.01%?>acorn flour?31.47%?,indicating that endogenous polyphenols inhibit starch digestion.For the A-,B-,and C-type starches,the addition of polyphenol extracts reduced the hydrolysis rate of starch,and the effect of FPA was better than that of BPA.