Azarpazhooh, Ramaswamy - Osmotic Dehydration
sional phenomena to promote mass transfer (Fito et al., 2001). When a vacuum pulse is
applied in the system, the gas and liquids in the internal pores of the product are re-
placed by the external liquid, and the impregnation process is completed practically by
the external solution, resulting in changing the mass transfer behavior in the product
due to its porosity reduction (Fito, 1994). When VI is applied, the mass loss is reduced as
compared with the process carried out at atmospheric pressure. Moreover, the process
yield is increased due to less mass loss in comparison with atmospheric pressure. In ad-
dition, the products enrich are enriched with nutrients, vitamins, minerals, incorporate
additives; in many cases, the sensorial properties of the product are improved (Chiralt et
al., 2001a). Vacuum impregnation has a great influence on product characteristics such
as the internal ratio, water loss and solid gain (Barat et al., 2001b; Chafer et al., 2001).
Deng and Zhao (2008) reported the significant effect of pulsed-vacuum on depress-
ing aw, titratable acidity, and in improving L value of the osmo-dehydrated apples. Va-
cuum osmotic dehydration (VOD) and pulsed-vacuum osmotic dehydration (PVOD), re-
duces the process time and energy costs (Deng and Zhao, 2008). Laurindo et al. (2007)
developed a device for measuring the dynamics of the vacuum impregnation (VI)
process. The device can measure the net force emitted by a food and transfer it to the VI
process by a load cell. Determination of water in this system during the VI process is not
required which increases the accuracy of the results. The experimental device can satis-
factorily quantify the influence of the vacuum level, something that is very important for
food process design. Vacuum impregnation (VI) processes reduced the process time
(approximately 85%) and the weight loss (approximately 48%), increasing yield
(Larrazabal-Fuentes et al., 2 009 ). Furthermore, it is a minimally processed method in
which the organoleptic characteristics of products and their shelf life are enhanced (Fito
et al., 2001; Correa et al., 2010). Pulsed vacuum osmotic dehydration (PVOD) is a new
method which is applied for a short (normally 5 min) vacuum treatment to a fruit dip-
ped in an osmotic solution, and after that the osmotic dehydration is done at atmospher-
ic pressure. The benefit of this method is that it reduces energy costs (Panadés et al.,
2006 ). Castelló et al. (2010) investigated the effect of osmotic dehydration on the me-
chanical and optical properties of strawberry halves by applying (PVOD) and adding cal-
cium. They reported that calcium addition and PVOD treatments had beneficial effects
on the maintenance of the sample texture during storage. In addition, the sample porosi-
ty was greater due to the treatment (vacuum impregnation) results in modifying the
color of strawberries. According to (Fito et al., 2001; Barat et al., 2001a; Chafer et al.,
2003 ; Giraldo et al., 2003) higher effective diffusivity values are obtained with the appli-
cation of the vacuum pulse and with a decrease in the osmotic solution concentration.
Correa et al. (2010) reported higher weight loss of osmotically dehydrated guavas dur-
ing application, higher sucrose solution concentrations and the vacuum pulse. They re-
port that solid uptake was favored by vacuum application. Increasing the osmotic solu-
tion concentration induces an increase in the mass transfer (Barat et al., 2001a; Giraldo
et al., 2003; Panadés et al., 2006; Ito et al., 2007).
4.4.5. Application of pulsed electrical field as a pretreatment
The pulsed electric field (PEF) as a non-thermal method has been reported to in-
crease permeability of plant cells with positive influence on mass transfer in further