Total Porosity and Open‐pore Porosity in the Drying of Fruits

Abstract

A simple procedure has been implemented to measure porosity of apples as a function of moisture contents. The method has been applied to apples with change in moisture contents by conventional air drying. It is shown that the pores, which for biological reasons are open, i.e. connected to the outside, at the onset of dehydration, remain so until X = 1.5 g/g. As dehydration proceeds the pores are split into two families of pores: externally connected pores and locked-in bores. Both total and open pore porosity can be predicted from experimental correlations. Alternatively, the total porosity can be estimated from data on bulk volume shrinkage and the average composition of the tissue by means of equations presented. The interpretation of experimental data using this approach confirms that there is a significant change in the three-dimensional arrangement of the cellular tissue below X = 1.5 g/g. The two approaches lead to the conclusion that, probably due to cellular collapse, the open structure that characterizes the fresh foodstuff changes into a structure with locked-in pores. This fact may help to explain the slow and difficult re-hydration which characterizes air-dried foodstuffs. This hypothesis will be followed up in future work. The information developed should be of help in qualitative and quantitative modeling of processes involving moisture changes.

Mathematical modeling of drying process of unripe banana slices

“…Different authors have investigated the change in apparent density of starchy materials during drying and found similar results (MAROUSIS; SARAVACOS, 1990;BRENNAN, 1995;YAN et al, 2008). Shrinkage is responsible for the Therefore, the apparent density of the sample decreases with decreasing moisture content at low moisture contents (WANG; BRENNAN, 1995), which is completely correlated with the porosity behavior in Fig.…”

“…Rahman; Potluri (1991) presented a more general form of correlation than Mattea; Urbicain; Rotstein (1986) and Lozano et al (1980) for correlating their data on squid meat during air drying by normalizing both sides of correlation with initial water content before drying, as it is presented in this study.…”

“…Experimental values of these properties are also essential in modeling and design of various heat and mass transfer operations. Marousis and Saravacos (1990) investigated the density and porosity in drying starch materials. A polynomial function of moisture content was fitted to the density data.…”

“…The experimental data were correlated using the following equation of the form: Lozano et al (1980) correlated the apparent and substance density of apple during air drying by an exponential equation for whole range of moisture content.…”

Drying rates in shrinking medium: case study of banana

“…The initial and final volume and the apparent density were determined by weighing the samples in air and a liquid of known density, following procedure described by Lozano et al (1980). The initial values of volume and density were determined from control samples from the same fruit that the dried sample.…”