Effect of porosity on rehydration of dry food particulates

Abstract

Rehydration of food particulates is a complex phenomenon affected by numerous factors that typically include pre-drying treatments, mode of dehydration, structure, composition and medium viscosity. Freeze drying (FD), air drying (AD) and their combinations, were utilized to produce an array of porosities, ranging from very high to very low values for FD and AD carrots, respectively. Bulk porosity correlated significantly with open, but not with closed, porosity. Bulk and open porosities decreased with AD time. Scanning electron micrographs of the FD samples verified their organized and more open structure in comparison with the AD carrots. Rehydration ratio increased with bulk and open porosity, and was not affected by the closed porosity. The effective moisture diffusivity, derived from fitting the normalized Weibull distribution, increased with bulk and open porosity and was about two orders of magnitude higher for the FD, than for the AD, carrots. The Weibull shape parameter, β, was inversely related to porosity. Its values indicated that water uptake of only the AD carrots followed a Fickian diffusion. A critical porosity value above which water mechanism changed from a Fickian diffusion to imbibition into a porous medium is suggested.

Instant vegetable from osmo-air drying of jimikand (A. campanulatus) in NaCl solution: nutritional, functional, micro-structural and other quality aspects

“…This may be due to cell permeabilization by high osmotic stress (Lewicki 1998) and blockage of pores due to higher solute gain. The porous microstructure and porosity play an important role in the rehydration mechanism (Marabi and Saguy 2004). After rehydration of fresh hot-air dried and osmo-air dried jimikand samples % solutes lost in solution left after rehydrated was observed.…”

The effect of packaging material and storage period on microwave-dried potato (Solanum tuberosum L.) cubes

“…Water transport in foods is an important physical process during drying, storage and rewetting, and significantly affects the quality of food products and the transport of water within porous foods (Marabi and Saguy 2004). A porous microstructure and porosity are two important factors in the mechanism of rehydration since capillary imbibition plays an important role in the uptake of water while a reduction in the number and size of pores decreases rehydration properties and higher bulk porosity increases rehydration values (Marabi and Saguy 2004).…”

“…A porous microstructure and porosity are two important factors in the mechanism of rehydration since capillary imbibition plays an important role in the uptake of water while a reduction in the number and size of pores decreases rehydration properties and higher bulk porosity increases rehydration values (Marabi and Saguy 2004).…”

“…The first stage of rehydration is quick, and then the rate of water absorption gradually decreases (Marabi and Saguy 2004). Moreover, during rehydration, vitamins, sugars, amino acids, and minerals decrease (Maldonado et al 2010).…”

“…Marabi and Saguy (2004) studied the effect of blanching in deionized water at 90°C for 5 min and drying in air on fresh carrots (cv. 'Concerto') that had been cut into 0.4 cm thick slices, before drying was completed using freeze-drying to a final moisture content of 30 g/kg (wet basis): air-dried period increased, causing bulk and open porosity to decrease, and rehydration to decrease.…”