Molecular Dynamic Simulation Study on the Effects of Moisture Content on the Water Activity and Glass Transition Temperature of Food Carbohydrates

L. Abudour
General Mills,
United States

Keywords: food, food carbohydrates, molecular modeling


Food systems behavior is strongly dependent on the thermodynamics and kinetics of water in the system. Understanding changes in the location and mobility of water represents a significant step in food stability knowledge since water ‘‘availability’’ profoundly influences the chemical, physical and microbiological quality of foods. In this work, molecular simulations are carried out in CULGI to predict the physiochemical properties of carbohydrate aqueous solutions, particularly at high sugar concentrations where experimental measurement can be difficult. Atomistic molecular dynamics (MD) simulations are used to calculate the glass transition temperature (Tg), water activity (aw), and diffusion behavior of binary mixture of water and low molecular weight carbohydrates including glucose, fructose, sucrose, and maltose. Coarse-grained dissipative particle dynamics (DPD) simulations are used to simulate large and complex systems in an efficient and inexpensive manner when compared with full-atom molecular dynamics (MD). Specifically, DPD simulations are used to model high-molecular-weight carbohydrates (polydextrose) and a multiple carbohydrate mixture (honey), with a final MD step to estimate the diffusion coefficient and density of polydextrose and honey as a function of the water content. Required intra- and intermolecular parameters of the DPD simulations are automatically generated using the automated fragmentation and parametrization protocol. MD and DPD Simulations are carried out at 10 K intervals over a range of temperatures above and below the expected glass transition temperature of the studied carbohydrate solutions for different water concentrations. The density and diffusion coefficient as a function of temperature are used to estimate the glass transition temperatures. The plots of density and diffusion coefficient versus temperature show a discontinuity at a specific temperature. The temperature at the discontinuity is taken as the simulated Tg value for the carbohydrate–water mixtures. The water activity and Tg values determined by the MD and DPD molecular simulations are compared with the experimental values in the literature and the comparison shows good agreement between calculated and experimental values. Accordingly, the molecular simulation method used in this work is not only a useful tool to provide properties of a given carbohydrate/water mixtures but also a promising technique to help screen the formulations of carbohydrate polymer and water for targeted properties and applications.