TY - JOUR
T1 - Role of glass-transition on fluid transport in porous food materials
AU - Takhar, Pawan S.
N1 - Funding Information:
Author Notes: Author has previously published as Pawan P. Singh. Thanks to USDA-NRICGP for providing financial support under the award number 2003-35503-13963.
PY - 2008/8/27
Y1 - 2008/8/27
N2 - Many food materials such as pasta, potatoes, starch, corn, soybeans, food gels etc. exhibit glass transition in the range of industrial temperature and fluid content values during transport processes such as drying, sorption, cooking, frying etc. Glass transition plays a critical role in affecting the fluid distribution profiles inside the food and average rate of fluid uptake by the whole food matrix. Yet this phenomenon is not included in most modeling studies that are primarily based upon Fick's law of diffusion. The purpose of this communication is to elucidate that Fick's law is valid only when the food is in glassy or rubbery states. Near glass-transition, the relaxation time of polymers is of the order of diffusion time. Thus, time-dependent conformational changes in food biopolymers add an extra stress term to fluid flow. Keeping track of this stress term is also the key to predict quality changes (related to food texture, physical state and crust formation) in foods via modeling. Based upon the average moisture and temperature at a given instant, even if the entire food matrix exists in a specific mechanical state in an average sense, its different sub-regions may be glassy, rubbery or in glass transition state. For example, during sorption, as a fluid front penetrates through a glassy food matrix, regions ahead of the front will be glassy. Regions in the proximity of the moving front would be undergoing glass transition and the regions already saturated by the fluid would be in a rubbery state. In the proximity of the moving front, where glass-transition is taking place, the fluid flow behavior is non-Fickian. During drying of biopolymers these regions will be in reverse order with the outer surface in a glassy state, center in a rubbery state and the middle region in transition state. Here a continuum mechanics based modeling approach is presented that can be used to predict fluid profiles and normalized stress profiles in all three states (glassy, rubbery and transition).
AB - Many food materials such as pasta, potatoes, starch, corn, soybeans, food gels etc. exhibit glass transition in the range of industrial temperature and fluid content values during transport processes such as drying, sorption, cooking, frying etc. Glass transition plays a critical role in affecting the fluid distribution profiles inside the food and average rate of fluid uptake by the whole food matrix. Yet this phenomenon is not included in most modeling studies that are primarily based upon Fick's law of diffusion. The purpose of this communication is to elucidate that Fick's law is valid only when the food is in glassy or rubbery states. Near glass-transition, the relaxation time of polymers is of the order of diffusion time. Thus, time-dependent conformational changes in food biopolymers add an extra stress term to fluid flow. Keeping track of this stress term is also the key to predict quality changes (related to food texture, physical state and crust formation) in foods via modeling. Based upon the average moisture and temperature at a given instant, even if the entire food matrix exists in a specific mechanical state in an average sense, its different sub-regions may be glassy, rubbery or in glass transition state. For example, during sorption, as a fluid front penetrates through a glassy food matrix, regions ahead of the front will be glassy. Regions in the proximity of the moving front would be undergoing glass transition and the regions already saturated by the fluid would be in a rubbery state. In the proximity of the moving front, where glass-transition is taking place, the fluid flow behavior is non-Fickian. During drying of biopolymers these regions will be in reverse order with the outer surface in a glassy state, center in a rubbery state and the middle region in transition state. Here a continuum mechanics based modeling approach is presented that can be used to predict fluid profiles and normalized stress profiles in all three states (glassy, rubbery and transition).
KW - Fickian
KW - Fluid transport
KW - Glass transition
KW - Non-Fickian
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U2 - 10.2202/1556-3758.1526
DO - 10.2202/1556-3758.1526
M3 - Article
AN - SCOPUS:55549127574
SN - 1556-3758
VL - 4
JO - International Journal of Food Engineering
JF - International Journal of Food Engineering
IS - 7
M1 - 5
ER -