osmotic dehydration technique for the preservation of fruits and vegetables

In recent years much attention has been focused on maintaining the freshness of fruits and vegetables by immersion of cellular materials containing water in an osmotic solution. It results in the development of intermediate moisture products having lower water activity, which is imparted by solute gain and water loss. During the process, chemical, physical and biological activities, which deteriorate the foods, are lowered considerably; hence extends the shelf life of food products. In this process moisture is withdrawn from the product at ambient temperature by diffusion, so phase change has been avoided. dehydrated vegetables

These techniques have been employed during or after osmotic treatment to enhance osmotic dehydration performance by increasing the cell membrane permeability and mass transfer rate.

These techniques have been employed during or after osmotic treatment to enhance osmotic dehydration performance by increasing the cell membrane permeability. These combined operations reduce the drying time, minimizing further energy costs as well as improving the quality of fruits and vegetables during storage.

When a food material is dipped in a hypertonic solution, the cells in the first layer of the material contact the solution and start to lose water due to the concentration gradient between the hypertonic solution and the cells, which lead to shrinkage of the material. After the loss of water from the cell of the first layer, a chemical potential difference of water develops between the first layer cells and second layer cells.

Application of osmosis in food processing Osmotic dehydration technique has mostly been utilized to develop new products, as it affects the nutritional and sensory properties of fresh fruits and vegetables (Khan, 2012; Phisut, 2012; Tortoe, 2010). It also maximizes the sugar to acid ratio and enhances the stability of pigments and texture during drying and storage (Rastogi et al., 2005). The sugar uptake of low molar mass sacharides (glucose, fructose and sucrose) is high due to maximum diffusion rate of molecules. This method produces a gentle processing of fruits and vegetables, because of their greater sensory resemblance between the dehydrated and natural products.

Types of osmotic agent

The osmotic dehydration process is affected by the physicochemical properties, molecular weight, solubility and ionic state of solute (Lenart, 1992; Lazarides, 1994). It serves as a driving force for the countercurrent flows of solute and water, as well as measure the extent of water loss and solid uptake. It significantly affects the physical and sensory properties of the final product.

Industrial Relevance

The osmotic dehydration technique is gaining popularity as a mean of obtaining minimally processed food. This review paper deals with the kinetics and mechanisms of osmotic dehydration technique for the preservation of fruits and vegetables.

Variables such as variety,maturity level and geometry of the food materials as well as pretreatments, temperature,concentration and types of osmotic agent affect the mass transfer during osmotic dehydration.Application of processes such as pulsed electric field, high pressure, gamma-irradiation, vacuum,microwave, centrifugal force or ultrasound in conjunction with osmotic dehydration technique accelerated the mass transfer and drying rates by the permeabilization of the cell membranes.