Glycosylation Remodeling and Thermal Denaturation Dictate the Functional Diversification of Protein Z

Protein Z (PZ) derived from barley malt has been identified as one of the key proteins contributing to foam stability. Recently, PZ was also recognized as an effective carrier, a functionality attributed to its serpin-like activities. This study investigated key structural-functional changes in PZ during thermal processing (mashing and boiling). The structural modifications of PZ variants were analyzed using FT-IR (Fourier Transform Infrared Spectroscopy). The results indicated that the secondary structure of PZ, after mashing, did not change significantly, whereas the β-turn content of PZ after boiling increased to 24.08% ± 0.34%. Interfacial adsorption kinetics, coupled with structural analysis, revealed that PZ, after mashing, exhibited the highest foamability (41.4 ± 0.38%), which was associated with the highest diffusion rate constant (K_diff) (1.05 ± 0.03). In contrast, PZ after boiling demonstrated superior foam stability (68.54 ± 1.12%), which correlated with the highest rearrangement rate constant (K_R) (-6.13 ± 0.06). Moreover, PZ, after mashing, exhibited enhanced inhibitory activity, an effect associated with the removal of glycosylation at Thr344 and Thr350 (located in the reactive center loop of PZ) via enzymatic hydrolysis during the mashing process. In contrast, PZ after boiling resulted in a loss of thrombin inhibitory activity, consistent with protein denaturation at high temperatures. These findings elucidate how structural modifications affect the function of PZ during brewing, thereby providing a scientific foundation for its potential applications across multiple fields.