Ultrasound-Assisted Maillard Glycosylation of Zophobas morio Protein–Maltodextrin Conjugates: Effects on Structure and Acid-Induced Gel Properties

In this study, we investigated the effect of ultrasound-assisted Maillard glycosylation reaction time on the structural, physicochemical, and acid-induced gel properties of Zophobas morio protein–maltodextrin (ZMP–MD) conjugates. Ultrasound treatment up to 45 min (100 kHz, 450 W, 70 °C) significantly accelerated the conjugation efficiency (15.81%) compared to that of wet heating at 70 °C for 6 h (13.62%) (p < 0.05). Fourier transform infrared spectroscopy (FT-IR) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses confirmed that both Maillard glycosylation methods formed ZMP–MD conjugates. In addition, the results for secondary structure, surface hydrophobicity, and zeta potential revealed that the ultrasound treatment promoted greater protein structural unfolding, decreasing α-helix while increasing β-sheet and random coil content compared to wet heating. These changes in structural and physicochemical properties of ZMP–MD conjugates impacted the glucono-δ-lactone (GDL)-based acid-induced gel properties. Even though Maillard glycosylation with MD weakened gel properties compared to native ZMP, the gel obtained after 45 min of ultrasound treatment exhibited a higher storage modulus, gel strength, and water-holding capacity than the wet-heated ZMP–MD gel. In conclusion, these findings suggest that properly controlled ultrasound-assisted Maillard glycosylation can modify protein structure, potentially improving its gel properties.