Louise Slade and Harry Levine were among the first scientists to use concepts derived from material sciences to explain and to predict the stability of glassy or semi-crystalline food matrices, whether frozen or dry products. More precisely, the relevance of the glass transition temperature, Tg, as a reference temperature governing the lifetime of food has been demonstrated, whereas often only the water activity had been considered. Indeed, taking into account this dynamic transition makes it possible to explain textural changes in food products and is still very useful for the study of cereal based products. In the proposed presentation, we illustrate with two examples of actual cereal products (waffles and extruded breakfast cereals), how elements of thermodynamics (sorption / desorption isotherm) and dynamics (Tg and relaxation times) can be combined to go deeper in the management of the impact of more or less amount of plasticizers (water and sucrose) on structure evolution. The results obtained by the conventional techniques (sorption isotherm, calorimetry, mechanical and dielectric spectroscopies) will be revisited to analyze the impact of the composition on the structure and the dynamics in the materials studied; thus, the possible identification by DSC of two glass transition phenomena for the same matrix will be discussed. In a less conventional manner, examples of the use of neutron scattering to extract tomographic data will be presented. The effects of physical aging during storage in the glassy state will be taken into account to understand the heterogeneities of the composite matrices at the molecular level as well as the different ability of the products to be hydrated as function of the environment.

Impact of sucrose and water contents on macroscopic structure and stability of cereal based products: Thermodynamic versus dynamic

255th National Meeting (2018)

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