Lactose crystallization and Maillard reaction in simulated milk powder based on the change in water activity

Maillard reaction (MR) and lactose crystallization (LC) are important reactions in the storage of milk powder. In this study, three models with different proteins based on skimmed milk powder were established to investigate the relationship between MR and LC at different water activities (a_w ). Moisture sorption isotherm, glass transition temperature (T_g ), and glycation products were evaluated, and the protein structure and lactose crystallinity were determined. The results indicated that MR product content, browning, and LC subsequently enhanced with the increase in a_w . The T_g value dropped lower than 0 at a_w 0.43 in whey protein isolate-lactose (WP-Lac) model and at a_w 0.54 in casein-whey protein isolate-lactose (CN-WP-Lac) model and casein-lactose (CN-Lac) model. The crystallinity of α-lactose monohydrate and anhydrous β-lactose in WP-Lac model was more significant than CN-WP-Lac and CN-Lac models (p < 0.05). The molecular band of whey protein gradually blurred in the Sodium dodecyl-sulfate polyacrylamide gel electrophoresis image, and the content of α-helix of WP-Lac model increased by 45.15% from a_w 0.33 to 0.53 (p < 0.05), while that of CN-WP-Lac model increased by only 3.95% (p < 0.05). With the increase in a_w , WP-Lac model formed more browning and crystallization products than CN-WP-Lac model, indicating that the presence of micelle macromolecules and the interaction between casein and whey proteins limited the browning and crystallization in CN-WP-Lac model. Practical Application Maillard reaction and lactose crystallization are important reactions in the storage of milk powder, and the result will provide theoretical guidance for the development of milk powder in the food industry.