Its about use of Osmotic dehydration in food processing, its principle, factors affecting OD, advantages and disadvantages of OD process, impact of OD on quality properties of fruits

1. OSMOTIC DEHYDRATION OF FRUITS
Presented By Amaresh
M.Tech in Food process Engineering
Agricultural and Food Engineering Department
IIT Kharagpur

2. CONTENTS
1. Introduction
2. Principle
3. Factors affecting osmotic dehydration
4. Enhancement of osmotic dehydration
5. Advantages and disadvantages
6. Impact of osmotic dehydration on quality
properties
7. Conclusion
8. References

3. Introduction
 Osmotic dehydration is the process of water removal by
immersion of water containing cellular solid in a
concentrated aqueous solution.
 Osmotic dehydration has been recognized as a good pre-
treatment prior to regular drying.
 Osmotic dehydration has the potential to remove water at
low temperatures.
 It is an energy efficient method, as water does not go
through a phase change.

4.  It gives rise to three types of simultaneous
counter current flows-
 Water diffusion into the solution
 Solute diffusion into food
 Leaching out of the product's own solutes

5. Why Osmotic Dehydration ??
Dehydration Osmotic dehydration
1. Sensorial properties are
affected.
2. Loss of flavor
3. Huge nutrients loss.
4. Chance of physical
contamination
1. Sensorial properties are very
good
2. Retention of fresh fruit flavors.
3. Retention of nutrients.
4. No chance of contamination
Hence, for improved quality & Ready To Eat products
osmodehydration is the best choice!!!

6. DEHYDRATED FRUITS

7. OSMOTICALLY DEHYDRATED FRUITS

8. OSMOSIS
water or
dilute solution
concentrated
solution
membrane
More water passes from
dilute to concentrated ...
...until concentrations
become equal
level riseslevel falls

9. Fig.1. Mass transport during osmotic dehydration.

10. Because there are more freely moving water molecules on
the left, more diffuse through the pores of the membrane
from left to right than from right to left.
membrane
water sugar solution

11. Fig.2. Typical osmotic dehydration system configuration

12. Factors affecting osmotic dehydration
 Type of osmotic agent
 Concentration of the osmotic solution
 Time of treatment
 Temperature of the osmotic solution
 Size and geometry of the material
 Solution-to-material mass ratio
 Level of agitation of the solution

13. Osmotic agent Remark References
Calcium
chloride
Increase firmness of apple pieces,
preserve the texture during storage.
Ponting et al.
(1972)
Lactose Has much lower level of sweetness
than sucrose & Low solubility in
aqueous solution.
Hawkes and Flink
(1978)
Sodium chloride Retards oxidative and non enzymatic
browning. Sometime bleaching
effects on colored products.
Khin et al. (2007)
Singh et al. (2007)
Sucrose Dry sugar is unsuitable due to
oxidative browning. Difficulty in
disposing the sugar syrup formed.
Flink (1975)
Mixture of
sucrose and salt,
ethanol and salt
More effective than sucrose alone
due to combination of properties of
both the solutes.
Lenart and Flink
(1984a, b)
Type of osmotic agent

14.  Concentration of the osmotic solution
 High concentrations of solution and long osmotic times
increased the penetration depth of osmotic agents and
decreased the moisture content of samples.
 Time of treatment
 The rate of both moisture loss and solids gain is the
highest for first 2 hour followed by progressively lower
rates for the rest of the time.
 Rapid loss of water in the beginning is due to the large
osmotic driving force between the fresh fruit and the
surrounding hypertonic solution.

15. Temperature of the osmotic solution
 Higher process temperatures promote faster moisture
loss through better mass transfer characteristics on the
surface due to lower viscosity of the osmotic medium.
 However, above 45°C, enzymatic browning and flavour
deterioration begins to take place.
 The best processing temperature depends on type of
food:
example, for green beans, 20°C gives better results,
while 40°C is too high a temperature.

16. Fig.3. Effect of solute type & concentration on water loss

17. Fig.4.Effect of solute type & concentration on solid gain

18. • Size and geometry of the material
 The surface area to volume ratio has been shown to be
the influencing factor with higher ratios favoring better
osmotic dehydration rates (Islam and Flink ,1982).
• Solution-to-material mass ratio
 As the solution to sample ratio increased, the osmosis
rate increased up to a certain level and then level off .
 The weight ratio of solution to product most often used
is between 4 and 10.
• Level of agitation of the solution
 The osmotic dehydration is faster when syrup is
agitated. This is because of reduced mass transfer
resistance at the surface.

19. Enhancement of osmotic dehydration
 Application of microwave during osmotic dehydration
 Application of vacuum as a pretreatment
 Application of blanching as a pretreatment
 Application of high hydrostatic pressure as a
pretreatment

20. Application of ultrasound in osmotic
dehydration
 Ultrasound can travel through a solid medium;
therefore, it can influence mass transfer.
 A phenomenon known as acoustic cavitation is
generated during the application as ultrasonic waves
can generate minute vapor-filled bubbles that collapse
rapidly or generate voids in liquids. Consequently,
rapid pressure fluctuations are induced within the wet
material by the ultrasonic waves.

21. Application of microwave during osmotic
dehydration
 Material absorbing microwave energy directly and
internally and converting it into heat.
 Moisture outflux effectiveness of the microwaves in
immersion mode is reduced due resistance of medium
itself for absorption of microwaves.
 The spray mode uses a thin layer of osmotic solution
that is continuously flushed down.
 This eliminates the problem of sample floating.

22. Fig.5.microwave /vacuum drying

23. Application of blanching as a pretreatment
 Hot water or steam blanching is a pretreatment before
osmotic dehydration with the purpose of
 Enzyme inactivation
 To promote gas removal from surfaces and
intercellular spaces
 Prevention of oxidation, discoloration, and off-
flavour development and microbial growth.
 Water blanching (85–100 °C) usually results in loss of
nutrients such as minerals and vitamins (Akyol et al.,
2006).

24. Application of high hydrostatic pressure as a
pretreatment
 High-pressure treatments can be applied to liquid
and solid foods, with or without packaging, at
pressures between 100 and 800 MPa.
 High pressures cause permeabilization of the cell
structure leading to the enhancement of mass
transfer rates during osmotic dehydration.
 Akyol et al. (2006) showed that high hydrostatic
pressure with the combination of mild heat
treatment can be used for blanching purposes in
carrots, green beans, and green peas.

25. Advantages
 Quality improvement in terms of color, flavor and
texture
 Lower energy requirements
 Packaging and distribution cost reduction
 Retention of nutrients during storage
 This provides better retention of volatile flavours and
reduces tissue damage compared with conventional air
and sun drying processes.

26. Disadvantages
• The reduction in acidity level reduces the
characteristic taste of some products. This can
overcome by adding fruit acid in the solution.
• Sugar coating is not desirable in some products and
quick rinsing in water may be necessary after the
treatment.
• Osmotic dehydration with other combined processes
such as vacuum drying, air drying or blanching were
found expensive
• It is a time taking process

27. Impact of osmotic dehydration on texture and colour
 During osmotic de-hydration, the viscous natures of
fruits and vegetables increase while their elasticity de-
creases due to the sugar uptake.
 Osmotic dehydration improves fruit quality by
stabilizing color parameters and allows less color loss of
fruit by enzymatic oxidative browning due to infusion
of extensive sugars.
 This provides better retention of volatile flavours.

29.  Treatments T1 and T2 did not cause any differences in the
aroma (p > 0.05).
 The lower acceptance of the fruits from treatment T3 is
due to the presence of aromatic compounds in the syrup
caused by caramelization due to the drastic inversion rate.
 For flavour, the fresh fruit had the highest mean value,
although this did not differ for treatment T1 and T2.
 The lower acceptance of the fruits from treatment T3 can
be attributed to losses in sensory quality of the syrup
during the inversion process, since its inversion rate was
much higher than that of T2.

30.  The mango in natura has higher mean for texture but the
other treatments acceptance was low. Probably the
process conditions (45ºC and 4 h) were drastic, resulting
in lower sensory quality products.
 The mangos osmo-dehydrated with treatment T2 had
overal acceptance scores similar to those of mangos in
natura.
 Treatment T2 was the most adequate treatment for the
osmotic dehydration of mango.

31. Conclusion
 Food applications of the osmotic dehydration process
provide a potential to apply energy efficient
procedures on an industrial scale.
 Osmotic dehydration has a tremendous market
potential for producing high quality food with
different variety.

32. References
 Akyol, C., Alpas, H., Bayındırlı, A., 2006, Inactivation of peroxidase and
lipoxygenase in car-rots, green beans, and green peas by combination of
high hydrostatic pressure and mild heat treatment, European Food
Research and Technology, 224(2), pp.171-176.
 Islam, M.N., Flink, J.N., 1982, Dehydration of potato 2: Osmotic
concentration and its effect on air drying behavior, Journal of Food
Technology, 17(3), pp. 387-403.
 Lenart, A., Flink, J.M., 1984a, Osmotic concentration of potato, 1. criteria
for the endpoint of the osmosis process, Journal of Food Technology,
19(1), pp. 45-63.
 Lenart, A., Flink, J.M., 1984b, Osmotic concentration of potato, 2. spatial-
distribution of the osmotic effect, Journal of Food Technology, 19(1), pp.
65-89.
 Ponting, J.D., Walters, G.G., Forrey, R.R., Jackson, R., Stanley, W.L.,
1966, Osmotic dehydra-tion of fruits, Food Technology, 20, pp. 125-128.
 Drying of Foods Vegetables and Fruits Volume 1 by Sachin V. Jangam,
Chung Lim Law and Arun S. Mujumdar.