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

The effects of mixing orders of tannic acid (TA), starch, and alpha-amylase on the enzyme inhibition of TA were studied, including mixing TA with alpha-amylase before starch addition (order 1), mixing TA with pre-gelatinized starch before alpha-amylase addition (order 2) and co-gelatinizing TA with starch before alpha-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 alpha-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, alpha-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.

Automated summary

The mixing order of tannic acid with alpha-amylase before starch addition resulted in the highest enzyme inhibition, while mixing tannic acid with pre-gelatinized starch or co-gelatinizing tannic acid with starch decreased the inhibition by reducing the binding of tannic acid with the enzyme. The differences in inhibition at low and high tannic acid concentrations between the two mixing orders were attributed to the adsorption properties of pre-gelatinized and co-gelatinized starch.