THE EFFECT OF OSMOTIC DEHYDRATION PRETREATMENT ON VACUUM
DRYING RATES OF VEGETABLES
G.Dons , G.Ferrari, P.Di Matteo
University of Salerno, Department of Chemical and Food Engineering
Via Ponte Don Melillo - 84084 Fisciano (SA) Italy
Tel. +39(89)964134 fax +39(89)964057
e-mail: ferrari@dica.unisa.it
Keywords: osmotic dehydration, combined processes, rehydration, vegetables.
ABSTRACT
Osmotic dehydration has recently received considerable attention due
to its possible utilization as pre-treatment stage before further
processing of fruits and vegetables.
The scope of such pre-treatment is that of obtaining high quality
dehydrated products and low energy requirements of the overall dehydration
process, preserving fruits and vegetables from thermal damages. Moreover,
the improvement of textural properties, flavor retention and color
stabilization without sulfite addition is also obtained as a result of this
kind of pre-treatment. Several literature studies are related to the
application of osmotic dehydration before drying processes such as air
drying and freeze drying. However, only in few papers the rehydration
behavior of osmo-dried fruits and vegetables is discussed.
This paper reports experimental results obtained during vacuum drying of
osmotically dehydrated and fresh vegetables. Osmotic dehydration curves are
determined using different sugar/salt solutions. Different solute
concentrations, also in presence of sodium chloride as osmolyte, are used
during experiments. Osmotic dehydrated samples are dried in a vacuum drier
and the effect of the osmotic pre-treatment on the drying rates is
determined and discussed. Dehydrated samples are rehydrated and rehydration
curves were also measured.
The osmotically pre-treated samples show a total drying time, which is
lower than that of fresh samples, as a consequence of the reduced initial
water content. The increase of the sodium chloride content increases the
osmodrying rates, but affects negatively the rehydration rates of products.
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