Characterizing moisture uptake and plasticization effects of water on amorphous amylose starch models using molecular dynamics methods.

• The OPLS3e force field for carbohydrates can reproduce experimental structural properties for amylose molecules. • Metadynamics calculations can be used to create torsional free energy maps. • Amorphous starch models can be used to predict moisture uptake. • Activation energies of water in starch agrees quantitatively with experiment. • Glass transition temperatures depression from H 2 O content matches experimental trends. Dynamics and thermophysical properties of amorphous starch were explored using molecular dynamics (MD) simulations. Using the OPLS3e force field, simulations of short amylose chains in water were performed to determine force field accuracy. Using well-tempered metadynamics, a free energy map of the two glycosidic angles of an amylose molecule was constructed and compared with other modern force fields. Good agreement of torsional sampling for both solvated and amorphous amylose starch models was observed. Using combined grand canonical Monte Carlo (GCMC)/MD simulations, a moisture sorption isotherm curve is predicted along with temperature dependence. Concentration-dependent activation energies for water transport agree quantitatively with previous experiments. Finally, the plasticization effect of moisture content on amorphous starch was investigated. Predicted glass transition temperature (T g) depression as a function of moisture content is in line with experimental trends. Further, our calculations provide a value for the dry T g for amorphous starch, a value which no experimental value is available. [ABSTRACT FROM AUTHOR]