Osmotic dehydration is an operation used for the partial removal of water from plant tissues by immersion in a

hypertonic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane- ...

(

osmotic Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region o ...

) solution. Sugar or salt solutions are used to reduce the moisture content of foods before actual

drying Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be consider ...

process. This technique is used to give the product quality improvement over conventional drying process. Mild

heat treatment Heat treating (or heat treatment) is a group of industrial process, industrial, thermal and metalworking, metalworking processes used to alter the physical property, physical, and sometimes chemical property, chemical, properties of a material. ...

after osmotic dehydration favours colour and flavour retention resulting in the product having superior

organoleptic Organoleptic properties are the aspects of food, water or other substances that create an individual experience via the senses—including taste, sight, smell, and touch. USDA uses In traditional U.S. Department of Agriculture meat and poul ...

characteristics. It also increases resistance to heat treatment, prevents

enzymatic browning Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regardin ...

and inhibits activities of

polyphenol oxidase Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in fruit browning, is a tetramer that contains four atoms of copper per molecule. PPO may accept monophenols and/or ''o''-diphenols as substrates. The ...

. The process is economical. Osmotic dehydration depends on: * Temperature of osmotic solution. * Concentration of the osmotic solution. * Osmotic agent used. * Process duration. * Geometry of food material.

Process

Water removal is based on the natural and non-destructive phenomenon of

osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region o ...

across

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

s. The driving force for the diffusion of water from the tissue into the solution is provided by the higher osmotic pressure of the hyper-tonic solution. The diffusion of water is accompanied by the simultaneous counter diffusion of

solutes In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent ...

from the osmotic solution into the tissue. Since the cell membrane responsible for osmotic transport is not perfectly selective, solutes present in the cells ( organic acids,

reducing sugar A reducing sugar is any sugar that is capable of acting as a reducing agent. In an alkaline solution, a reducing sugar forms some aldehyde or ketone, which allows it to act as a reducing agent, for example in Benedict's reagent. In such a reacti ...

s, minerals, flavors and pigment compounds) can also be leaked into the osmotic solution, which affects the

and nutritional characteristics of the product. The rate of diffusion of water from any material made up of such tissues depends upon factors such as temperature and concentration of the osmotic solution, the size and geometry of the material, the solution-to-material mass ratio and, to a certain level.., agitation of the solution.Rastogi,N.K., K.S.M.S.Raghavarao and K.Niranjan(2005). Developments in Osmotic Dehydration. Emerging technologies for food processing..

References

{{biology-stub Chemical processes Cell biology