Luz A. Pascual-Pineda

Fractal surface analysis and thermodynamic properties of moisture sorption of calcium–sucrose powders

ABSTRACT Fractal analysis, using water adsorption and an image analysis technique, was applied to investigate the effect of surface irregularities on the thermodynamic properties of matrix calcium–sucrose powder moisture sorption. The sorption isotherms were evaluated at 15, 25, and 35°C for calcium–sucrose powders obtained by a cryogenic process (CP) and spray drying (SD). Solubilization of the powders was observed after 20 days of storage at 25°C, and the powder CP had greater physical stability than SD. There was good agreement among the fractal dimension computed by scanning electron microscopy analysis and water adsorption isotherm. The surface fractal dimensions were between 2.19 and 2.44 for CP and were larger than those obtained for SD, which were between 2.11 to 2.26. The differential and integral enthalpies increased as the surface geometry became more irregular, also increased the interactions between the powder surface and water molecules. These results suggested that the increase in the matrix irregularities for a product can displace the minimum integral entropy toward high water activity, thereby improving the storage stability.

Food Preservation by Nanostructures-Water Interactions Control

Understanding structure–function properties in food systems has led to possibilities of food preservation by managing product structural features so that water and nutriments are subjected to various levels of physical immobilization, thus reducing reactivity and allowing a better control of product stability. In this chapter it is noted that to achieve this, it is necessary to induce in the solid matrix of the product the formation of micro–nano cavities, fissures, and pores into which water and other substances will strongly (and tightly) bound. Important thermodynamic characteristics of the system control this reduction in mobility and entropy control of food matrix-liquid is aimed to achieve the task. Also, principles and practical applications of such processes are discussed as well as structural features-appraisal methodologies.