Characterization of tryptic hydrolysis of α-lactalbumin/saponin mixture and structural change of α-lactalbumin interacting with soybean saponin

Bovine milk α-lactalbumin (α-La) was mixed with soybean saponin, and the resulting mixture was hydrolyzed by trypsin. Saponin increased the tryptic-hydrolysis level of α-La only at relatively high phosphate buffer concentrations (⩾0.05 M). T1 experiments with acetylated soybean saponin demonstrated that there were some interactions between α-La and saponin not only at high concentrations of phosphate buffers but even at low concentrations as well. Circular dichroism spectra of α-La showed that the tertiary structure of α-La was changed through interactions with saponin only at high buffer concentrations. Furthermore, by analyzing the tryptic peptides from an α-La/saponin mixture, hydrolyzing rates at all or some of K5, R10, and K16 of α-La were accelerated by saponin interactions. The increase in the tryptic hydrolysis of α-La by saponin addition was considered due to modification of the tertiary structure of α-La by saponin.