Topic Dehydration of fruits and vegetables Presented by: Miss Vaishali Wankhade Department of Agril. Process Engineering Dr. PDKV Akola

Introduction Dehydration/Drying: Methods of preservation Accomplish by the removal of water from fruits and vegetables containing 70- 95% water. Preserved fruits and vegetables for long time by affecting enzyme activity and growth of micro- organism Drying : removal of about below 15% of water, it is too high for long Storability. Dehydration: Complete removal of water by application of artificial heat under controlled condition of temp. , RH and air flow.

IMPORTANCE - Modern production technology has greatly increase yields of fruits and vegetables One–fourth of highly perishable fruits and vegetables are not consumed due to spoilage during storage transportation and processing Proper processing minimizes post harvest losses. Dehydrated fruits has less weight and required less space for storage so it is highly practicable for as military food.

Methods of dehydration of fruits and vegetables Osmotic dehydration Foam mat drying Freeze drying Infrared radiative drying

Osmotic dehydration it is nondestructive method to reduce water content and to improve quality of fruits and vegetables product. principle of osmosis is used. cut fruits or vegetables are immersed in concentrated solutions of sugars and salts. due to difference in concentration of these foodstuff and the solution it looses some quantity of water to the external solution. Rate of removal of water can be enhanced by increasing the concentration of the osmotic solution or the temperature. About 50% water is removed by this treatment. Further drying in convective or tray dryer is carried out.

Advantages of osmotic dehydration Minimized heat damage to fruits and vegetable while drying. Least discolouration of fruits by enzymatic browning. Increase retention of volatile, flavours and aroma. Improved textural quality and lower energy consumption than air drying.

Foam mat drying It is method of drying food. The liquid concentrate is whipped to a foam with the aid of a foaming agent, spread on a tray and dried in a stream of warm air. Material is dried rapidly with due to porous nature of the foam. Since evaporation is fast, high heat can be used without impairing flavour and colour. Process involved drying a continuous sheet of foams 10-40 µm thick on continuous and rapidly moving steam stainless steel belt. The product is heated to 75 oC within 40 sec and within 60 sec a dry product of 2-3 % moisture is obtained.

Fig. continuous type foam mat dryer

Freeze drying During the freeze-drying process, fresh or cooked foods are first flash frozen when the food tastes its best. Moisture is then removed in a vacuum chamber, where a low- level heat is applied to evaporate the ice without returning it to a liquid form. Since the product remains frozen during the process, the product’s cell structures do not change, which helps retain the freshness, vitamins, nutrients, colors, and aromas of the fresh foods. it offers shelf-stable convenience of long-term storage. This freeze-drying process allows for quick re-hydration of the product. Freeze-dried products are light; they typically weigh up to 90 percent less than the product’s original weight. Just add water and they are ready to use!

Infra- red radiative drying convective heating with air can release heat fluxes of only about 0.9 to 2.0 K watt/m2. Infra-red radiative heating produces heat fluxes of about 4.5 to 12.0 K watt/m2. this brings dehydration of fruits and vegetables in shorter periods at low temperature of 28oC as against 75- 80 oc with continuous radiative drying. combine convective and radiative drying is done for heat sensitive foods like fruit juices.

Schematic diagramm of experimental infra-red radiative and convective drying system

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