Physical Modification

Moisture diffusion can be enhanced by cutting the fruits and vegetable surface by

rupturing the cellwall or removing the resinous cellwall that deters the moisture transfer, as in

case of raisins, plums or prunes. Enhanced diffusion can also be achieved by sizing or cutting

into pieces, as it would increase exposed surface area to drying environment (Doymaz, 2008).

Since drying behaviour depends on the thermal and mass diffusivity, it is imperative to

consider size and shape of the food material prior to drying to improve the drying efficiency.

Piercing or abrasion of skin can also increase the diffusion, as this process will aid in

diffusion through the breakage of relatively impervious intact cellwall and chemical pre-

treatment can be avoided (Di Matteo et al., 2000). Jazini and Hatamipour (2009) have tried to

enhance the mass transfer rate during air-drying by piercing the plums. As compared to the

chemical dip of the plums in NaOH solution, the pierced plums dried faster. This provides an

insight how the chemical treatment can be avoided by opting for simpler physical methods.

Many fruits and vegetables are frozen prior to drying. On freezing the samples, the water

molecules form icicles, disrupt the cellular structure; on drying the larger icicles collapse. Since

the cellular matrix do not regain their original shape, water diffusion become faster during

dehydration process (Arévalo-Pinedo & Murr, 2007).