Agriculture Reference
In-Depth Information
I
NTRODUCTION
Osmotic dehydration is a process of partial removal of water, mostly from plant tissues
(fruits and vegetables), in the hypertonic solutions. Driving force for removal of water is the
difference in osmotic pressure between the plant material and the surrounding fluid. The
complex cellular structure of plant tissue behaves as a permeable membrane. The membrane
is not completely selective and as a result we have two opposing mass flow: the diffusion of
water from plant tissues in the surrounding solvent and solute diffusion from the solution in
plant tissue. The goal of osmotic dehydration is to achieve as greater flux of water from the
plant tissue, while reducing the flux of solute into the tissue. The most commonly used
solutions of sucrose and sodium chloride, as well as their combined solutions.
Osmotic dehydration as a pretreatment has the advantage over conventional drying
methods, since there is no change in the nutritional and functional properties of food, as well
as in its appearance (color, texture, sensory characteristics, etc.). Another important advantage
of osmotic dehydration over other drying methods is that it takes place without changing the
physical condition of the water, so that it is much more efficient in terms of energy savings to
the conventional drying methods that include water phase change.
Dietary fibers are edible parts of plants or analogous carbohydrates that are not digestible
and cannot be absorbed in the small intestine, but instead they are partially or completely
fermented in the colon of the human body. Fiber has the primary effect of the water uptake
and its introduction into the digestive system. Products rich in dietary fiber in the mouth give
a feeling of fullness, while in the stomach fibers slow down the movement of food to the
small intestine, causing a feeling of satiety. In the small intestine fibers slow down the
absorption of nutrient and in that way normalize lipid and glucose metabolism as the main
source of energy which in turn regulate energy balance between meals. In some cases, a diet
rich in fiber helps control diabetes, but it is one of the best-documented effects of their
positive effect on diverticulitis of the small or large intestine. Fibers often have a preventive
role, but they are part of a therapeutic diet.
The richest sources of dietary fiber from fruits: apples, oranges and bananas; vegetables:
cauliflower, cake, carrot, potato, tomato and boiled sweet corn. Sugar beet also represents a
significant source of dietary fiber. Primarily used fiber obtained from the extracted pulp
cossettes, but can be used and sweet beet cossettes that are added after drying to the cereal
mixtures for breakfast. In addition to the enrichment of such mixtures dietary fiber content,
adding sugar beet cossettes to such mixtures improves its taste due to present of sugar and
further sweetening is not required.
O
SMOTIC
D
EHYDRATION
Driving force for diffusion of water, during osmotic dehydration, from the tissues into the
solution provides a higher osmotic pressure of hypertonic solution compared to the osmotic
pressure that exists within the cells of plant tissue. Diffusion of water is accompanied by the
simultaneous counter diffusion of solute from the osmotic solution into the tissue. Since the
