Effect Of Tea Polyphenol On The Digestion Of High Amylose Maize Starch And The Mechanism

The research is on the influence and mechanism of tea polyphenol on the digestingsystem of high amylose corn starch, the results may find an effective way to make good use ofhigh amylose starch and tea polyphenols to prevent diabetes. The main research contents areas follows:The effect of the tea polyphenols (TPLs,10%HAC, w/w) with different ways ofadministration on the postprandial glycemic response to cooked high amylose corn starch(HAC) was investigated. The in vivo test using a mouse model showed an augmentedglycemic response to co-cooked high amylose corn starch (containing79.4%amylose) with10%TPLs (dry weight of starch). However, high amylose corn starch with different dosesTPLs before and after gelatinization showed some slowly digestible effect, the best of whichis high amylose corn starch with75mg/75mg TPLs before and after gelatinization respectively.The effect of different ways of TPL administration on the postprandial glycemic response tocooked high amylose corn starch might be caused by TPLs-enzyme interaction andTPLs-starch interaction, but this hypothesis needs to be verified in the further study.From the point of interaction between TPLs and starch digestive enzymes, the effects ofTPLs on the enzyme kinetics and the fluorescence characteristic of starch digestive enzymeswere investigated. The experimental results showed TPLs noncompetitively inhibit thepancreatic α-amylase activity (pH6.9) but activate the activity of amyloglucosidase (pH4.6)in a dose-dependent manner. The enzyme-substrate complex is likely the way for TPLs tobind and to inhibit the α-amylase reaction. However, TPLs can both bind to amyloglucosidaseand amyloglucosidase-substrate to affect enzyme reaction. Regarding the effects of TPLs onthe substrate inhibition of amyloglucosidase, TPLs increased the reaction rate at lowersubstrate concentrations, but augmented the inhibition efficiency at higher substrateconcentrations without changing the inhibition pattern indicating the binding of TPLs toamyloglucosidase affect both the catalytic site and the non-catalytic site. However, when bothenzymes were employed under the experimental condition of the Englyst test (pH5.2), aheterogeneous inhibition pattern was shown with a peak inhibition of~30%when the contentof TPLs was~2.5mg/mL and a negative inhibition at contents greater than4mg/mL, which isconsistent with a higher and lower degrees of starch digestion in the presence of5mg/mL and2mg/mL TPLs, respectively.From the point of interaction between TPLs and starch, the effects of TPLs on thephysiochemical properties of starches, the mechanism of TPLs-amylose interaction and theeffects of TPLs on the properties of high amylose corn starch during the course ofretrogradation were studied. The results showed that the effects of TPLs on the digestibility,the dynamic viscous elasticity of starches, and the TPLs’ binding capacity of starches wereintimately related to the amylose content indicating amylose is the main componentintercacting with TPLs in the starches. Furthermore, EGCG and ECG are the main monomerinteracting with amylose and they are likely to be positioned between amylose helices throughhydrogen bonding with good thermal stability. The results of TPLs’ affecting the properties of high amylose starch corn during the course of retrogradation showed that TPLs couldeffectively retard the short-term retrogradation caused by amylose gellation andcrystallization. The interaction between TPLs and amylose decreased gradually during thecourse of retrogradation, but the TPLs still existed between amylose helices. Thus, how tostabilize the TPLs-amylose interaction warrants further investigation for the practicalapplication of this system for functional food design.In conclusion, under the experimental dosages (10%HAC，w/w), TPLs can inhibit thestarch digestive enzymes, and TPLs-amylose interaction makes the high amylose corn starchbe easier to digest. These two effects lead to different postprandial glycemic responses tocooked high amylose corn starch when the same amount tea polyphenols (TPLs) areadministrated with different amount before and after gelatinization.