Azarpazhooh, Ramaswamy - Osmotic DehydrationThe rehydration process is typically composed of three simultaneous steps: absorption
of water into the dry material, swelling of the rehydrated product, and loss or diffusion
of soluble components (Lee et al., 2006). It is reported that increasing the rehydration
temperature in the range of 40– 8 0 °C for many fruits and vegetables, including bananas,
carrots, apples, potatoes, tomatoes, and yellow, red, and green peppers markedly in-
crease the volume of the product (Krokida and Marinos-Kouris, 2003). In order to de-
sign and optimize rehydration, different mathematic models can be used to describe
how certain process variables affect water transfer. Some researchers have assumed
simple least-squares adjustment to models based on exponential models or capillary
absorption theory, while others have used Fick’s diffusion laws, and demonstrated that a
model based on first-order kinetics can properly describe the gain of water during rehy-
dration (Krokida and Marinos-Kouris, 2003; Giraldo et al., 2006; Lee et al., 2006). There
are three methods to estimate rehydration characteristics of dehydrated products: (1)
water absorption capacity, WAC, which is the capacity of a matrix to absorb water that
replaces the water lost during drying (2) dry mass retention capacity, DHC, which is the
material ability to retain soluble solids after rehydration, and (3) rehydration ability or
capacity, RA, which is the ability of a dehydrated product to rehydrate, and which shows
total damage to tissues caused by drying and impregnation during rehydration
(Maldonado et al., 2010).
4.7. CONCLUDING REMARKS AND FUTURE RESEARCH NEEDS
Nowadays there is a heightened motivation that explains many recent advances in
the area of osmotic dehydration. Food applications of the osmotic dehydration process
provide a potential to apply energy efficient procedures on an industrial scale to pro-
duce mildly processed, high quality products. Osmotic dehydration has a tremendous
market potential for producing high quality food with different variety. It can also de-
velop fruit and vegetable ingredients with functional properties. However it is difficult
to define a general predictive processing model due to great variability of plant mate-
rials (species, cultivar, maturity stage, etc.). In addition there is lack of adequate res-
ponses to problems related to the management of the osmotic solutions (reconcentra-
tion, reuse, microbial contamination, reutilization, and discharge of the spent solution,
etc.), and developing continuous processing equipment. It is noteworthy that the appli-
cation of microwave osmotic dehydration viscous sugar solution makes the food pieces
float; agitation of the solution is therefore necessary. Lack of knowledge relevant to mi-
crobial development in both medium and processed product has been also mentioned.
REFERENCES
Ade-Omowaye, B.I.O., Rastogi, N.K., Angersbach, A., Knorr, D., 2001 , Effects of high hydros-
tatic pressure or high intensity electrical field pulse pre-treatment on dehydration charac-
teristics of red paprika. Innovative Food Science and Emerging Technologies, 2(1), pp. 1 - 7.
Akpinar, E.K., 2006 , Determination of suitable thin layer drying curve model for some vege-
tables and fruits. Journal of Food Engineering, 73(1), pp. 75 - 84.