Annemarie Schoonman

Solubility and diffusion of nitrogen in maltodextrin/protein tablets.

The gas transport properties of compacted tablets consisting of an amorphous mixture of maltodextrin and sodium caseinate were studied by dissolving nitrogen gas in the tablets and then determining the gas release over time as a function of temperature and water activity. Gas was dissolved in the tablet matrix by heating the tablets under pressure, generally to temperatures above the glass transition temperature of the matrix, holding them at these conditions for a specified time and then rapidly cooling them while maintaining the external pressure. The solubility of nitrogen was found to be largely determined by the free volume of the matrix, which in turn can be influenced to some degree by thermal and pressure treatments during gas loading. At the levels of free volume studied, the dissolved nitrogen is densely packed in the free volume, the packing density being virtually independent of the externally applied pressure. Release of gas from the tablets at temperatures below the glass transition temperature is generally well described by Fickian diffusion. The effective diffusion coefficient of gas release is strongly dependent on the microstructure and porosity of the tablet matrix, and an approximate model describing the relationship between tablet structure and rate of gas release is formulated. The model is in semiquantitative agreement with the rates of gas diffusion obtained for tablets and dense granules. Owing to the structural heterogeneity and variability of the tablets and the history‐dependent properties of the tablet matrix, the effective diffusion coefficients of gas release from the tablets showed a relatively large spread. The temperature dependence of diffusional release follows an Arrhenius relation below the glass transition temperature. This allows the prediction of the nitrogen retention in the tablets as function of time, temperature and pressure.

The microstructure of foamed maltodextrin/sodium caseinate powders: a comparative study by microscopy and physical techniques

Abstract Microscopy followed by image analysis is combined with physical characterisation techniques in order to obtain information about the structure of solid foams consisting of maltodextrin DE12 and sodium caseinate (10–30% w/w) processed under varying foaming conditions. Thin sections of solid foam were analysed by microscopy and image analysis for closed porosity, bubble size distribution and bubble connectivity. The bubble size distribution in the range up to about 25 μm was found to be largely independent of the degree of foaming. The total porosity of the solid foams, as determined by image analysis, was in very good agreement with the results from helium pycnometry and a direct relationship between the porosity and surface area as measured by BET nitrogen adsorption is obtained. Mercury intrusion porosimetry was found to be of limited use for the analysis of the open pore structure because of the fragility of the powders and the overlap in size between bubbles and interstitial spaces between the powder particles.