A molecular dynamics (MD) modeling and simulations approach
has been rationally developed to construct and study
amylose and dextran porous layers that could be considered good
physicochemical representations of food materials. This approach
could also be adopted in the construction and subsequent study
of food materials with varying numbers and types of monomers
per polymer chain. The findings from our MD studies indicate that
the presence of food macromolecules lowers the water–water
interactions for the nearby water molecules by reducing their
hydration numbers and disturbing their configurations, but also
provides new water–macromolecule interactions that can significantly
outweigh the partial loss of water–water interactions to
make the water molecules adjacent to the macromolecules
strongly bound and very likely non-freezable and corresponding
to low values of water activity aw. As a result, water molecules in
the pore space in porous food systems are not in the same
energetic and configurational states and, thus, most likely do not
have uniform distributions of water activity aw, water removal
rate, and dehydration energy and entropy requirements within
individual pores and cross-sectionally. These effects of pore
structures are found to be greater in food systems with higher densities
of food macromolecules, smaller in size pores, and stronger
water–macromolecule interactions. Based on the results and discussion presented in this work, dehydration of food materials
can be reasonably expected to be driven more by enthalpic effect
than by entropic effect, and to start from the largest pores and from
the middle regions of individual pores where the values of the
water activity locally are higher. As a result of these tendencies
and water surface tension, the water–vapor interfaces could be expected
to be non-planar inside individual pores as well as crosssectionally
and the water removal rates dependent on the lateral
distributions of pore sizes during food dehydration.