Determination of porosity and particle size of natural bulk materials using image analysis

Abstract

Porosity and particle volume are important properties of solids in numerous technical processes. Dehydration in food technology often leads to a decrease of particle size, combined with a change of porosity. Knowledge of the moisture dependence of these properties helps to avoid quality losses during drying. Common methods of porosity determination like mercury porosimetry or B.E.T. gas adsorption do not allow moisture variation. Therefore, a porosity evaluation method consisting of a combination of image analysis and gas displacement in a pycnometer is developed. Taking helium as the gas allows to measure open as well as encapsulated pore volume of the biological product. With particular consideration of basic geometrical particle shape of the investigated natural bulk materials, the disadvantage of image analysis being a two-dimensional measuring method is limited. Experimental results are of high reproducibility and show good agreement with literature data and a standard porosimetry method. Particle size prediction derived from a combination of particle volume balance and estimated porosity shows good agreement between calculated and measured particle size, even under variation of moisture content. This comparison also indicates the high reliability of the presented porosity analysis.

Physical Properties of Alginate−Starch Cellular Sponges

“…The particle density of the ground sample should be higher than the particle density of the whole sample if there are closed pores with air trapped in them (Lozano and Urbicain, 1980). It should be noted that helium gas, while determining the particle density, may penetrate some of the closed pores, especially in the beginning of the process, when the matrix is not very dense yet (Hinz and Eggers, 1996).…”

Tailor‐made porous solid foods

“…Another, less plausible, assumption could be related to the formation of casing and closed pores in the inner part of the gel after sugar diffusion and drying, resulting in reduced particle density. It is worth noting that when particle density is determined by means of a helium pycnometer, the derived porosity is composed of open pores (major fraction), and those closed cells which have also been penetrated by the gas (Hinz & Eggers, 1996).…”