Effect of glass transitions on the rheological properties of food polymers

Abstract

The rheological properties of food products are highly dependent on the physical state of the structural matrix, which ranges from the glassy state, the glass‐rubber transition region, the rubbery plateau region, the rubbery flow region, and viscous flow region. Depending upon the combination of temperature and/or moisture content, the viscosity could be anywhere from 1015 mPa.s for glassy material and 1 mPa.s for flowable, low viscosity liquid. During the glass transition range alone, the rheological properties can change as large as 1000 times. The rheological properties of ingredients, in‐process intermediates, and finished products also affect the processing techniques, textural quality, physical and chemical stability during storage. In this paper, the similarity in rheological behaviors between synthetic and food polymers, as affected by degree of crystallinity, cross‐linking, plasticization, and phase separation is reviewed. Various mathematical equations for modeling the changes in rheological properties during glass transitions are also discussed. The advantages and shortcomings of each model will also be compared.

Effect of moisture content on textural attributes of dried figs

“…Considering the moisture content of figs rehydrated at different temperatures (13.5-45.9%), all rehydrated figs are in rubbery state while the sun-dried figs (control sample) are in glass-rubber transition region. According to Huang (1999), the physical state of the structural matrix ranges from the glassy state to and through the following regions: glass-rubber transition, rubbery plateau, rubbery flow, and viscous flow, which greatly influences the rheological properties of food products. Even during the glass transition range alone, the rheological properties can change as much as 1000 times (Huang, 1999).…”

“…According to Huang (1999), the physical state of the structural matrix ranges from the glassy state to and through the following regions: glass-rubber transition, rubbery plateau, rubbery flow, and viscous flow, which greatly influences the rheological properties of food products. Even during the glass transition range alone, the rheological properties can change as much as 1000 times (Huang, 1999). Indeed, when the material transforms from the glassy to the rubbery state, the molecules become mobile, which can alter food structure and microstructure, crystallisation, rates of diffusion, stabilisation of microbial cells and spores, and chemical and biochemical reactions (Slade and Levine, 1991).…”