Since its inception, "Food Polymer Science" has transformed our understanding of the behavior of food systems, in particular by demonstrating the importance of the glass transition for the behavior of amorphous foods during processing, storage and consumption. While the glass transition temperature (T<sub>g</sub>) and its dependence on food composition and water content are now routinely applied in product development and in food stability analysis, numerous experimental observations, linked e.g. to the migration of water and other low molecular weight species, indicate that dynamic phenomena occur at appreciable rates in the glassy state. In order to shed light on these phenomena, we embarked about 15 years ago on an investigation of the structure of glassy carbohydrates using positron annihilation lifetime spectroscopy (PALS). These investigations have provided detailed insights in the change of the molecular free volume as a function of temperature, water content and carbohydrate composition, and have led to a structural interpretation of the impact of low molecular weight diluents, such as water, polyols and mono- and disaccharides, on amorphous carbohydrate glasses in terms of antiplasticization and plasticization. I will first review the main results obtained using PALS on such glassy matrices, and then extend the discussion by including results obtained from a range of additional techniques, such as infred spectroscopy, solid state NMR, neutron scattering and dielectric spectroscopy. Finally, I will attempt to link the regimes as identified via the structural and dynamic properties in order to formulate a general hypothesis for the mechanism of plasticization and antiplasticization of carbohydrate glasses by low molecular weight diluents.

Plasticization and antiplasticization in amorphous carbohydrates: A structural interpretation

255th National Meeting (2018)

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