Study On The Formation Mechanism Of Low Digestibility Of Starch-Quercetin In Tartary Buckwheat

During the processing,a large amount of starch（TBS）in Tartary buckwheat was gelatinized with quercetin to form a complex structure（TBSH）.The structure is an important factor that directly affects the quality of tartary buckwheat products.In this study,we found that TBSH has low digestibility,which can be used as a new way to control postprandial blood glucose,which is of great significance for the control of type 2 diabetes mellitus（T2DM）.It also provides a new theoretical basis for the development of hypoglycemic tartary buckwheat products.The main research conclusions are as follows:（1）TBS and quercetin were co-gelatinized（95℃,20 min）to explore the structure of the co-gelatinized complex.Scanning electron microscope（SEM）study showed that the microstructure of TBSH appeared obvious reticular cavity structure,and the cavity further increased with the increase of dosage It is suggested that quercetin may interact with starch chain during starch gelatinization.Furthermore,the interaction between them is mainly non covalent by fourier transform infrared spectroscopy（FT-IR）.When the content of quercetin was2-4%,the order degree of TBSH increased and its structure became more compact.Through the detailed study of the non covalent interaction of Iodine-binding capacity（IBC）and X-ray diffraction（XRD）,it is found that the interaction mode is V-type complex driven by non covalent force dominated by hydrophobic force and sandwich type inclusion complex driven by hydrogen bond.（2）The interaction of quercetin withα-amylase andα-glucosidase was studied by enzymology and spectroscopy.The half maximum inhibitory concentration(IC₅₀)values of quercetin onα-amylase andα-glucosidase were 270±3.13 and 544±9.01μg·m L^-1,respectively.The inhibition type of quercetin onα-amylase was competitive inhibition,and the competitive inhibition constant（K_i）was 203.94μg·m L^-1.The inhibition type ofα-glucosidase was mixed inhibition,K_i and non competitive inhibition constant(K_is)were 22.37 and 0.098μM,respectively;the maximum emission wavelength ofα-amylase andα-glucosidase induced by quercetin was obtained by fluorescence quenching.There was a little blue shift in water strength(λ_max)and enhanced hydrophobicity.In the study of synchronous fluorescence,with the increase of quercetin concentration,the fluorescence intensity of tryptophan（Try）and tyrosine（Tyr）residues inα-amylase andα-glucosidase decreased significantly（p<0.05）,especially for the quenching of Try.According to the calculation of the equation and its modified equation,there is only one/class binding site between quercetin andα-amylase/α-glucosidase.According to van’t Hoff equation,electrostatic force and hydrogen bond were the main binding forces of quercetin toα-amylase/α-glucosidase,respectively.However,inα-glucosidase,the amide I band did not shift,while in amide III band,the characteristic peak shifted from 1242 cm^-1 to 1241 cm^-1;after the addition of quercetin,the random coil content ofα-amylase andα-glucosidase decreased significantly,resulting in the transformation of the secondary structure of the enzyme protein from irregular to ordered.The IC₅₀,K_i,λ_Max and Ka values obtained by enzymology and spectroscopy showed that the binding ability and inhibition ability of quercetin toα-amylase were stronger than that ofα-glucosidase.（3）The formation of co-gelatinized complex significantly reduced the content of RDS and increased the content of RS（p<0.05）.It was found that the initial digestion rate of starch was determined by the hierarchical structure of TBSH,and C_∞was also affected by other factors such as enzyme activity.For the release rate of quercetin in the digestive juice,it was found that the quercetin content of all samples increased sharply in the initial stage（0-40 min）,and reached the stable stage after different time.The addition of 3%quercetin released a medium content of quercetin,but had a longer stable period.Therefore,the release behavior of quercetin is the result of synergistic effect of the structure of starch gel and quercetin inhibiting enzyme activity.Pearson correlation analysis showed that SDS content was significantly correlated with starch short-range order（p<0.05）;iodine binding strength was significantly correlated with starch digestion rate（k）（p<0.05）;k,RDS and C_∞were significantly correlated（p<0.01）.The above results show that high content of quercetin will combine with starch chain and accumulate into tight structure of TBSH,which will delay the digestion rate.After hydrolysis by digestive enzymes,the structure of TBSH became loose and quercetin was gradually exposed to lightα-amylase andα-glucosidase,thus inhibiting enzyme activity.However,the ordered structure inhibited the accessibility of digestive enzymes to tbsh and reduced the release of quercetin from tbsh.Therefore,the enhanced resistance of TBSH to digestive enzymes is the joint effect of the ordered structure of tbsh and the inhibition of quercetin.