Physical and Chemical Changes of Dehydrated Foods - Essay Example

Rehydration can be considered as a measure of the injury to the material caused by drying and treatments preceding dehydration (Okos et al., 1992; McMinn & Magee, 1997a). Rehydration of dried plant tissues is composed of three simultaneous processes: the imbibition of water into dried material, the swelling, and the leaching of solubles (McMinn & Magee, 1997b; Lewicki, 1998).

It has been shown that (Steffe & Singh, 1980) the volume changes (swelling) of biological materials are often proportional to the amount of absorbed water. Fan et al. (1962) found that the gain in volume caused by water sorption equaled the volume of imbibed water. On the other hand, the moisture-induced swelling of soybean and pigeon pea grains was always less than the volume of sorbed water (Singh & Kulshrestha, 1987). Studies of the volume increase of semolina (Bhattacharya, 1995) and soybean showed that rehydration temperature markedly affected volume increase.

It is generally accepted that the degree of rehydration is dependent on the degree of cellular and structural disruption. During drying, Jayaraman et al. (1990) observed irreversible cellular rupture and dislocation, resulting in loss of integrity and hence, a dense structure of collapsed, greatly shrunken capillaries with reduced hydrophilic properties, as reflected by the inability to imbibe sufficient water to rehydrate fully.

The effect of the drying method on the viscoelastic behavior of dehydrated apple, banana, potato, and carrot during rehydration was examined under uniaxial compression tests by Krokida et al. (2000).

The objectives of this investigation were to test the hypothesis that a generalized model to describe the following structural properties during rehydration could be generated. The properties were true density, apparent density, porosity, and specific volume of dehydrated apple, banana, potato, and carrot during rehydration.