New insights into the indirect reduction of starch digestibility by L-theanine: Elucidation of the mechanism of α-amylase/α-glucosidase inhibition based on spectroscopic and computational perspectives

With the increasing number of patients with type II diabetes associated with starchy foods, the inhibition of starch digestion has become one of the most important strategies for limiting postprandial glucose elevation. However, indirect inhibition of starch digestibility through the starch digestive enzymes pathway remains poorly studied. Based on this, we found that L-theanine (THE) had the potential to inhibit starch digestive enzyme activity and investigated the mechanism based on multi-spectral and computer simulations. The results showed that the half-inhibitory concentration (IC 50 ) values of THE on α-amylase and α-glucosidase were 1.22 mmol/L and 2.77 mmol/L, respectively, which exhibited a mixed type of inhibition. Fluorescence quenching results and analyses showed that the mechanism of inhibition of THE with digestive enzymes had both static quenching, mainly based on non-covalent interactions such as van der Waals forces and hydrogen bonding, with binding energies of −3.19 and −7.76 kcal/mol, respectively (Molecular docking results). The multi-spectral analysis showed that the binding of THE changed the secondary structure of starch digestive enzymes and the conformation of polypeptide chains, thus inhibiting the activity. The findings of this study are expected to guide the development of food products with hypoglycaemic function using THE.