Abstract: To provide a theoretical basis for developing high-performance emulsifying protein ingredients, this study investigated the glycation of casein from Qula cheese using lactose as the sugar donor under dry heating conditions and elucidated the impact of glycation on the structure and emulsifying properties of casein. Single-factor experiments were employed to optimize the reaction conditions. The degree of grafting, emulsifying properties, and hydrophobicity of the products were determined. The products were characterized using Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD) spectroscopy, and scanning electron microscopy (SEM). The results indicated that the highest glycation efficiency was achieved at a lactose-to-casein mass ratio of 1:1, a temperature of 60 ℃, and a reaction time of 6 h. Under these conditions, the degree of grafting reached 31.5%, and the emulsifying activity index (EAI) and emulsion stability index (ESI) were 81.0 m2/g and 88.2 min, respectively. Compared with unmodified casein, the surface hydrophobicity of glycated casein decreased by 21.4%, while its EAI significantly increased by 37.8%. Structural analyses revealed a decrease in α-helix and β-sheet contents and an increase in random coil content. After glycation, the compact block-like structure of native casein was transformed into a loose and porous network structure with reduced and more uniformly distributed particle sizes. Dry-heat glycation modification effectively improves the emulsifying properties of casein. The underlying mechanism is closely related to protein unfolding and improved amphiphilicity. This study provides a theoretical foundation for the high-value utilization of casein from Qula cheese.

Key words: Qula; casein; glycation; emulsifying properties; spectroscopy