Improving gas-water interface properties and bioactivities of α-lactalbumin induced by three structurally different saponins

Characterization of binding interactions, gas-water interface properties and bioactivities in α-lactalbumin (αLa) with tea saponin (Ts), gynostemma saponin (Gyp) and tribulus saponin (Tr) were elucidated by using molecular docking, multi-spectroscopic techniques, polarization biomicroscopic and cryo-electron microscopic analysis. Specifically, the static quenching ability to intrinsic fluorescence of αLa decreased according to the order of Ts, Gyp and Tr. Among them, αLa interacted with Ts and Gyp through hydrogen bond and van der Waals force, while it combined with Tr via hydrophobic interaction force. Furthermore, Ts, Gyp and Tr made foaming ability of αLa increased by 164.54%, 136.73% and 63.95%, respectively. Under cryo-electron microscope, the descending order of foam integrity and liquid film thickness was αLa-Gyp, αLa-Tr, αLa-Ts. Moreover, the DPPH scavenging ability, ferrous reducing power, and α-glucosidase inhibition of αLa-saponins were higher than those of αLa, and αLa-Ts showed the maximum. Meanwhile, molecular docking indicated that there were different binding sites and numbers between αLa and three saponins. And αLa-Ts, αLa-Gyp and αLa-Tr had 12, 3 and 6 hydrogen bonds, respectively. Moreover, Ts did not significantly affect secondary structure of αLa, whereas Gyp and Tr decreased its α-helix and increased its random coil. The obtained results provided basic data supports for interaction mechanism between natural saponins and proteins, being beneficial to develop efficient and natural protein-saponin foaming agents for food industry.