Essay On Dehydration

Dehydration is a form of drying under controlled conditions of temperature, humidity and air flow (Cruess, 1958). Since ancient time, dehydration has been one of the most common natural and reliable methods for food preservation. Sugar, honey and salt have been used as aids in the drying of fruits and vegetables at various times in the past (Goldblith, 1972; Woodroof, 1986). However, sugar was used to preserve the quality of the dried product, usually in small amounts, rather than as a means of removing water. Various studies have addressed the problems related to traditional convective drying. Drying has an impact on physical properties of the products which include loss of colour (Chua et al., 2000), change of texture, chemical changes affecting flavour and nutrients and shrinkage (Mayor and

Lazarides (1994) carried out studies on the osmotic dehydration of apples using 45 and 65 °Brix of sucrose solution. It was found that a higher sucrose concentration (65°Brix) led to faster water loss (ca.30% increase).

Physico-chemical properties of food material The chemical composition (protein, carbohydrate, fat and salt), physical structure (porosity, arrangement of cells, fibre orientation and skin) and pre-treatments may affect the kinetics of osmosis of food (Islam and Flink, 1982).

Geometry of food material The geometry of sample pieces affects the behavior of the osmotic concentration due to the variation of the surface area per unit mass and diffusion length of water and solutes involved in mass transfer (Lerici et al., 1985).

Immersion time The immersion time is significant factor affecting the osmotic dehydration. In general, rate of mass transfer is rapid in the early stages of the osmotic process after which the gradual slow down with time towards equilibrium end point has been reported (Conway et al., 1983; Lazarides, 1994; Uddin et al., 2004).

Advantages of osmotic