Developments in 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 In this process moisture is withdrawn from the product at ambient temperature by diffusion, so phase change has been avoided. Besides, it helps to improve the nutritional and sensory attributes of food products and is less energy intensive process as compared to other drying techniques. Osmotic dehydration is influenced by various factors such as osmotic agent, time and temperature, solute concentration, solution to sample ratio, agitation and geometry of the materials. Recently, osmotic dehydration has been combined with several other methods namely, pulsed high electric field, high hydrostatic pressure, ultrasound, centrifugal force, vacuum and gamma irradiation. 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 combined operations reduce the drying time, minimizing further energy costs. In this study, various segments of osmotic dehydration techniques and its application in food processing as well as recent advances in osmotic dehydration have been reviewed. 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. The various factors effecting osmotic mass transfer rate in food have been reviewed. In this paper, the combined effect of osmotic dehydration and several other innovative techniques (pulsed high electric field, high hydrostatic pressure, ultrasound, centrifugal force, vacuum and gamma irradiation) on the quality and shelf life of fruits and vegetables have been reviewed. 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.