Quantitative Analysis of Molecular Mobility in Amorphous Lactose Above T: A Novel Insight from Molecular Dynamic...

Measuring molecular mobility (M) in solid food is challenging due to the rigid and heterogeneous nature of these matrices. The thermodynamic parameter Strength (S) fails to account for molecular displacement distances. This study emphasizes the role of molecular dynamic (MD) simulation in quantifying M on amorphous lactose at mimic water activities (a) at temperatures above the glass transition temperature (T), incorporating the S. The results show that coordinating root mean square displacement (RMSD) effectively quantifies M across different a and temperature conditions. Both increased a and higher temperatures facilitate M by expanding free volume and reducing energy barriers for molecular rearrangement, as indicated by the mobility coefficient calculations. This study also emphasizes the importance of system size in interpreting M, as larger systems exhibit emergent behaviors that smaller systems cannot capture. The calculated MD relaxation time for 10,000-molecule lactose/water cells at a specific S value was successfully translated to a real timescale of 1.8 × 10⁶ s, consistent with experimental data (1.2 × 10⁶ s). Moreover, water can shift from a plasticizing role to a more stabilizing one, slowing molecular motion and leading to equilibrium clustering. These findings have important implications for understanding the behavior of amorphous lactose in food and pharmaceutical formulations.