Factors Affecting The Digestibility Of Hydrothermal-treated Starch And Its Mechanism

Starch is the main energy source for both humans and monogastric mammals,the rate and extent of starch digestion is closely related to the postprandial blood glucose concentration response and the risk of type 2 diabetes.In-depth understanding of the factors and mechanisms that affect the processing of starch digestibility can prevent and control some chronic diseases.This study first studied the relationship between multi-scale structure and in vitro digestibility of lotus seed starch with different degrees of gelatinization(DG).Secondly,by comparing the digestibility differences of three different crystal forms of wheat.potato and lotus starch under low enzyme activity and high enzyme activity,the combination of enzyme and starch and the mechanism of catalytic hydrolysis were revealed.The research results are as follows:Sixteen lotus seed starch(LSS)samples with gelatinization degree from 0-100%were prepared by controlling the moisture content and heating temperature.With the increase of DG,the long-range and short-range molecular order of lotus seed starch were gradually destroyed.The "Malta cross" phenomenon presented under the light microscope(PLM)was getting weaker and weaker until it disappeared.The in vitro digestion rate constant of starch increased with increasing DG.In order to reveal the cause of the difference in in vitro digestibility of the three starches under high enzymatic conditions,the average fluorescence intensity(FI)of?-amylase labeled with fluorescein isothiocyanate(FITC)was determined by laser confocal microscopy,and it was found that there was a positive correlation between DG and FI of potato and lotus starch.Potato starch(R2=0.99)was stronger than lotus seed starch(R2=0.54).In contrast,no linear correlation was observed between DG and FI of wheat starch,consistent with the in vitro digestibility of starch under high enzyme activity conditions.These results indicate that DG is the main determinant of the digestion rate of PS and LSS under high enzyme activity conditions,but the digestibility of WS is not affected by DG,and the combination of enzyme and substrate is a key step in the digestion process.Furthermore.the affinity(Km)and catalytic efficiency(keat/Km)between ?-amylase and starch samples of three different DG were analyzed from the perspective of amylase kinetics under low enzyme conditions.It was found that both affinity and catalytic efficiency increased with the increase of DG.It indicated that the ordered structure of starch in the hydrothermal treatment process was gradually destroyed,leading the accessibility of?-amylase to starch is gradually increased.The in vitro digestibility assay was repeated under low enzyme activity conditions.Unlike the above in vitro digestion results with high enzyme activity,it was found that the in vitro digestion rates and extents of the three starches increased with the increase of DG,which was consistent with the enzyme kinetics experimental results.It is indicated that the in vitro digestibility of the three starches was affected by the degree of gelatinization in the presence of only ?-amylase and low enzyme activity.