The Physical Adsorption of Gelatinized Starch with Tannic Acid Decreases the Inhibitory Activity of the Polyphenol against α-Amylase.

Yueyi Wang,Shuangshuang Li,Fangting Bai,Lijun Sun,Junwei Cao

doi:10.3390/foods10061233

Abstract

The effects of mixing orders of tannic acid (TA), starch, and α-amylase on the enzyme inhibition of TA were studied, including mixing TA with α-amylase before starch addition (order 1), mixing TA with pre-gelatinized starch before α-amylase addition (order 2) and co-gelatinizing TA with starch before α-amylase addition (order 3). It was found that the enzyme inhibition was always highest for order 1 because TA could bind with the enzyme active site thoroughly before digestion occurred. Both order 2 and 3 reduced α-amylase inhibition through decreasing binding of TA with the enzyme, which resulted from the non-covalent physical adsorption of TA with gelatinized starch. Interestingly, at low TA concentration, α-amylase inhibition for order 2 was higher than order 3, while at high TA concentration, the inhibition was shown with the opposite trend, which arose from the difference in the adsorption property between the pre-gelatinized and co-gelatinized starch at the corresponding TA concentrations. Moreover, both the crystalline structures and apparent morphology of starch were not significantly altered by TA addition for order 2 and 3. Conclusively, although a polyphenol has an acceptable inhibitory activity in vitro, the actual effect may not reach the expected one when taking processing procedures into account.

Highlights

Postprandial hyperglycemia is an important factor that causes disturbance of glucose metabolisms, like type II diabetes
Starchy foods are the main source of carbohydrates for human beings, the digestion of which decides the changes of postprandial blood sugar level to a large extent. α-Amylase is a key carbohydrate-hydrolyzing enzyme that initially catalyzes starchy components, producing reducing sugars, such as maltose, maltotriose, maltooligosaccharides, etc., and these reducing sugars are further hydrolyzed by α-glucosidase to glucose that is absorbed by enterocytes in the small intestine [1]
By taking three common processing procedures of polyphenols, starch, and α-amylase in actual case into account, the effects of mixing orders on the inhibitory activity of tannic acid against α-amylase were explored in this study

Summary

Introduction

Postprandial hyperglycemia is an important factor that causes disturbance of glucose metabolisms, like type II diabetes. Inhibiting the activity of α-amylase by introducing exogenous enzyme inhibitors has been considered effective in controlling blood glucose level after meals through delaying starch digestion [2]. Α-amylase inhibition of a phenolic compound results from noncovalent binding interactions between them, mainly including hydrogen bondings and π-π conjugations [4,5]. This way, the factors that affect polyphenol–amylase binding interactions are considered to cause the changes in the inhibitory activity of polyphenols; for example, there is a structure–activity relationship for flavonoids regarding α-amylase inhibition as the difference in flavonoid structures results in the difference in binding affinity of the polyphenols to the enzyme [5,6]. More factors that influence polyphenol–amylase binding and influence the inhibiting effect need to be explored to give a better understanding for further developing the inhibitory activity of a phenolic compound

Methods

Discussion

Conclusion