Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 417923
Title Effect of morphology on water sorption in cellular solid foods. Part II: sorption in cereal crackers
Author(s) Esveld, D.C.; Sman, R.G.M. van der; Witek, M.M.; Windt, C.W.; As, H. van; Duynhoven, J.P.M. van; Meinders, M.B.J.
Source Journal of Food Engineering 109 (2012)2. - ISSN 0260-8774 - p. 311 - 320.
Department(s) FBR Food Technology
Food Process Engineering
Publication type Refereed Article in a scientific journal
Publication year 2012
Keyword(s) moisture diffusivity - porous product - composite food - tortuosity - migration
Abstract Experimental dynamical moisture profiles of crackers with a fine and coarse morphology are successfully predicted using a pore scale network model. Experimental profiles are obtained using a single point imaging (SPI) NMR technique that enables 3D mapping of the moisture content of relatively immobile water at low water activity. The relative vapor conductivity trough the structure is 33% and 64% for the fine and coarse structured crackers, respectively. It can be argued that this is due to their difference in cell connectivity and not directly related to their difference in average cell diameter (0.33 and 0.75 mm, respectively). It was found that the retarded local sorption dynamics of the solid matrix has a noticeable influence on the moisture profiles that arise in the first hours. This is crucial for the moisture sorption dynamics of sub centimeter size samples, for which there is a distinct non-equilibrium between the vapor and the sorbed water phase. The local sorption at low water activity is a factor 3 faster for the fine structure cracker compared to the coarse one. This is due to their differences in average lamellae thickness (54 and 93 µm, respectively). However, for the description of the overall moisture sorption dynamics of the few cm thick samples, on a time scale of days, it valid to assume local equilibrium and to use an effective diffusivity model. The relative vapor conductivity together with the porosity and the derivative of the sorption isotherm determines the effective moisture diffusivity for these open structures, which is a factor 3 lower for the fine structured cracker compared to the coarse one. The single sided moisture sorption in the 2.5 thick cracker samples is not even completed after 5 days, mainly because at higher water content (near 20%) there is very little gradient in relative humidity to drive the vapor transport. This is reflected in the predicted effective moisture diffusivities which for the coarse cracker decrease from 16 × 10-9 m/s2 (at 1% MC, 16% aw) to 7.6 × 10-10 m/s2 (at 20% MC, 86% aw). --------------------------------------------------------------------------------
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