Optimization of deamidation of casein by protein-glutaminase and its effect on structural and functional properties

Abstract

Casein is a commonly used protein in the food industry, and its related products are abundant, such as beverages, desserts, but the further application of casein is limited by its solubility and stability. This study aimed to optimize the deamidation of casein using Protein-glutaminase (PG) and investigate its impact on the structure, solubility and stability of casein. Through center composite experiments, the optimal conditions for PG deamidation were determined to be at pH 6.0, E/S 15 U/g, and a temperature 45°C. The deamidation process alters the secondary structure of casein, resulting in a decrease in α-helix structure and an increase in β-sheet structure. The modification of casein improved emulsifying activity at pH 8.0 and pH 10.0, and significantly enhanced solubility at 5.0 to 6.0. Furthermore, the deamidation of casein leads to an increase in zeta potential and a decrease in particle size, resulting in improved stability of the protein solution due to reduced particle aggregation. The 3% deamidated casein based beverage with carrageenan exhibited reduced precipitation rates compared to the control after sterilization at 121°C for 15 min. In summary, PG deamidation offers a promising method to modify casein, enhancing its functional properties, including solubility, stability and emulsifying activity, thereby expanding the use of casein in the food industry.