ABSTRACT
Introduction ........................................................................................................ 593
Free Volume Theory .......................................................................................... 594
Modification to Account for the Effect of Water Activity ........................... 595
Materials and Methods ..................................................................................... 597
Mechanical Spectrometry Experiments.................................................. 597
Stress Relaxation Experiments and Time-Temperature
Superposition Principle......................................................................... 597
Diffusion Experiments............................................................................... 598
Results and Discussion ..................................................................................... 598
References ........................................................................................................... 600
Many food processes, which affect food quality and stability, are diffusion
controlled (Karel et al., 1994; Roos, 1995). Transport of key penetrants such as
water into or out of a polymeric food matrix can play a critical role in food
quality and stability. Water is one of the major components and a very good
plasticizer in foods. The quality and stability of dehydrated products, multi-
domain foods, and the performance of biofilms and encapsulation and
controlled release technologies are affected by moisture transport. The rates
of molecular mobility and diffusion-limited reactions strongly depend on the
factors surrounding the food. Temperature and water activity ða
Þ play
significant roles in penetrant diffusion. The physical state of the carrier
matrix, chemistry, size, and structure of diffusing molecule and specific
interactions between the matrix and penetrant also affect diffusivity.
Therefore, it is necessary to quantitatively predict the effects of temperature,
water activity, physical properties, and phase/state transitions of biopoly-
mers and physical/chemical interactions on the diffusion of solutes in
biological polymers.
