The
advantages of osmotic dehydration are that mild heat
treatment favours less heat damage to colour and
flavour of the product with superior sensory attributes.
The use of sugar or syrup as osmotic agent prevents
much of the loss of flavour commonly found with ordinary
air or vacuum drying. Enzymatic and oxidative browning
is prevented as the fruit pieces are surrounded by sugar,
thus making it possible to retain good colour with little
or no use of sulpher dioxide. Energy consumption is
much less as no phase change of moisture is involved
during dehydration. Osmotic dehydration with syrup
re-concentration demands two to three times less
energy compared to convection hot air drying. Acid
removal and sugar uptake by the fruit pieces modify
the composition (sugar to acid ratio) and improve the
taste and acceptability of the final product. It partially
removes water and thus reduces water removal load at the
dryer. It increases solid density due to solid uptake and
helps in getting quality product in freeze-drying. If salt
is used as an osmotic agent, higher moisture content is
allowed at the end of the drying as salt uptake
influences the water sorption behaviour of the product.
The final product shows lower hygroscopicity and
better textural quality after rehydration in comparison
to other dehydration techniques. The storage life of the
product is greatly enhanced. Simple equipment is
required for the process (Islam and Flink, 1982;
Chaudhari et al., 1993; Ghosh et al., 2004).